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diff --git a/40411-8.txt b/40411-8.txt deleted file mode 100644 index 1bed946..0000000 --- a/40411-8.txt +++ /dev/null @@ -1,5039 +0,0 @@ -The Project Gutenberg EBook of The Potter's Craft, by Charles F. Binns - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Potter's Craft - A Practical Guide for the Studio and Workshop - -Author: Charles F. Binns - -Release Date: August 4, 2012 [EBook #40411] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE POTTER'S CRAFT *** - - - - -Produced by Mark C. Orton, tallforasmurf and the Online -Distributed Proofreading Team at http://www.pgdp.net - - - - - - - - - -TRANSCRIBER'S NOTE - -In the numerous chemical formulae a subscripted number is shown as _{2}, -so the familiar formula for water would be H_{2}O: H, subscript 2, O. -This notation is needed to distinguish digits that are subscripts from -digits that are multipliers, as for example in the formula -Pb(OH)_{2}2PbCO_{3}, where the subscript 2 must be distinguished from -the quantity multiplier 2 that follows it. - - - - -[Illustration: _Frontispiece_ STONEWARE MADE BY THE AUTHOR.] - - - - - The Potter's Craft - - A Practical Guide for the Studio and Workshop - - _By_ CHARLES F. BINNS - - _Director of the New York State School of Clay-Working - and Ceramics_ ¶ _Some time a Superintendent in the - Royal Porcelain Works, Worcester, England_ - - _SECOND EDITION_ - _SECOND PRINTING_ - - _26 PLATES AND 20 TEXT ILLUSTRATIONS_ - - [Colophon] - - NEW YORK - D. VAN NOSTRAND COMPANY, INC. - EIGHT WARREN STREET - - - Copyright, 1910, 1922 - by - D. Van Nostrand Company - - _All rights reserved, including that of translation - into the Scandinavian and other foreign languages._ - - Printed in the United States of America - - LANCASTER PRESS, INC. - LANCASTER, PA. - - - - - "A book is written, not to multiply the - voice merely, not to carry it merely, - but to perpetuate it. The author has - something to say which he perceives to - be true and useful, or helpfully - beautiful. So far as he knows, no one - has yet said it; so far as he knows, no - one else can say it. He is bound to say - it clearly and melodiously if he may; - clearly, at all events." - - --_Ruskin._ - - - - -PREFACE TO SECOND EDITION - - -Since the publication of the first edition of this book eleven years -have elapsed, years packed full of varied and interesting experiences. - -During that time it has been the pleasant fortune of the author to -conduct classes, especially summer classes, in the science and art of -pottery production. These have been occasions of meeting many fine and -noble personalities whom to know is a liberal education. As one of the -consequences of these experiences the book has been revised and some new -chapters have been written. Especial acknowledgments are due and are -gratefully made to Elsie Binns for the chapter on Clay-Working for -Children and to Maude Robinson for that on Alkaline Glazes. - -The photographs are by the Taylor Studios, Hornell, N. Y. - - C. F. B. - Alfred, New York. - March, 1922. - - - - -PREFACE TO FIRST EDITION - - -This Book is the outcome of an experience extending over a period of -thirty-six years. Twenty years ago it would have been impossible, for -the science of ceramics was not then born. Ten years ago it would have -been wasted for the Artist-potter in America had not arrived, but now -the individual workers are many and the science is well established. - -Written teaching must be imperfect, but I have endeavored to set down -the exact methods by which my students are taught, in the hope that -those who cannot secure personal instruction may read and understand. - -As far as possible didactic statements have been avoided and the attempt -has been made to lead every student to experiment and to think for -himself. In other words, I have tried to erect sign-posts and occasional -warnings rather than to remove all obstacles from the road. - - C. F. B. - Alfred, N. Y. - January, 1910. - - - - -CONTENTS - - - Introduction.--The Present Need xiii - - CHAPTER - - I. Applied Art 1 - - II. Pottery 9 - - III. Porcelain 23 - - IV. The Nature and Properties of Clay 29 - - V. The Preparation of Clay 37 - - VI. Mold-Making and Plaster 43 - - VII. Cases and Working Molds 58 - - VIII. Building by Hand 68 - - IX. The Potter's Wheel 74 - - X. Turning 99 - - XI. Making Large Pieces 107 - - XII. Cups and Saucers and Plates 124 - - XIII. Casting 129 - - XIV. Tiles 133 - - XV. Glazes and Glazing - - Part I 140 - - Part II--Matt Glazes 152 - - Part III--Fritted Glazes 157 - - Part IV--Recipes 160 - - Part V--The Defects of Glazes 164 - - Part VI--Alkaline Glazes 167 - - XVI. Decoration 173 - - XVII. The Fire 179 - - XVIII. High Temperature Wares 188 - - XIX. Clay-working for Children 194 - - INDEX 201 - - - - -LIST OF PLATES - - Frontispiece.--Stoneware made by the Author. - PLATE. PAGE - I. Throwing.--Lesson II, 1 80 - II. Throwing.--Lesson II, 2 81 - III. Throwing.--Lesson II, 3 82 - IV. Throwing.--Lesson III, 1 83 - V. Throwing.--Lesson III, 2 86 - VI. Throwing.--Lesson IV, 1 87 - VII. Throwing.--Lesson IV, 2 89 - VIII. Throwing.--Lesson V 90 - IX. Throwing.--Lesson VI, 1 92 - X. Throwing.--Lesson VI, 2 93 - XI. Throwing.--Lesson VII 95 - XII. Throwing.--Lesson VIII, 1 96 - XIII. Throwing.--Lesson VIII, 2 97 - XIV. Making Large Pieces. The First Section 109 - XV. Making Large Pieces. Measuring the Foundation of the 110 - Second Section - XVI. Making Large Pieces. Drawing up the Second Section 111 - XVII. Making Large Pieces. Shaping the Third Section 112 - XVIII. Making Large Pieces. The Three Sections Completed 113 - XIX. Making Large Pieces. Turning the Edge of the First 114 - Section - XX. Making Large Pieces. Finishing the Bottom of the First 116 - Section - XXI. Making Large Pieces. Checking the Size of the Second 117 - Section - XXII. Making Large Pieces. Fitting Together Dry 119 - XXIII. Making Large Pieces. Setting the Third Section in Place 120 - XXIV. Making Large Pieces. The Three Sections Set Together in 121 - the Rough - XXV. Making Large Pieces. The Finished Vase 122 - - - - -INTRODUCTION: THE PRESENT NEED - - -Many times it has been proven, in the history of the world, that it is -not possible to force a reform or a novelty upon an unwilling people. -Such things are organic. In order to live they must grow and in order to -grow must live. No attempt will be made, therefore, in these pages to -foster an idea or propound a thought which may exist only in the -predilection of the author. - -The trend of the present demand, a persistent growth of several years, -is towards a personal and individual expression in the crafts or -industrial arts. This tendency is the natural swing of the pendulum from -the machine-made product of the manufactory which in its turn was the -inevitable result of mechanical invention. - -When the artisan was an artist and the designer a craftsman, there was -but a limited production of industrial art. The articles made were -expensive and for the wealthy alone. The common utensils necessary to -the household were made on the farm and were of the rudest possible -character. But with the gradual development of machinery there came an -abandonment of rural activities, a flocking to the city, manufacturing -on a large scale, lower prices, and a huge output. This has, of course, -taken many years to develop, but the utmost limit of the swing has been -reached and the question is "What next?" Will the factory cease its -labors? Will output decrease in bulk and improve in quality? Will there -ever, in a word, be a return to medieval conditions? Not only may all -these questions be answered in the negative but it may be stated with -all sincerity that there is no need for any other answer. - -What then, are not manufactured products as now put forth a menace to -the art life of the nation? Are not the people being educated in the use -of and belief in machine-made ornament and meretricious display? Perhaps -so, but no good purpose will be served by a ruthless condemnation of -these things. Art appreciation is a most subtle thing and no one may -dictate to his neighbor as to what he should or should not admire. It -took time for the public to understand and patronize the product of the -machine even though the price was favorable. It will take time for an -appreciation of craftsmanship to influence the land but this -consummation will most assuredly come. - -On the one hand there is the manufactory, teeming with "hands," riotous -with wheels, turning out its wares by the thousand and supplying the -demand of the many; on the other, there is the artist-artisan. He labors -at his bench in sincere devotion to his chosen vocation. His work is -laborious and exacting, he can make but a few things and for them he -must ask a price relatively high. Both these conditions are necessary. -The craftsman cannot supply the need of the people and the manufacturer -has no time or thought for disinterested production. Herein lies the -need and here is the mission of the individual worker. - -In every age it is given to some to discern more than the multitude and -it is theirs to teach. The people are anxious to learn, are eager to be -led. What they demand will be manufactured and so by the irresistible -lever of public opinion the man at the bench, if he be true to himself -and to his craft, may move the millionaire manufacturer to make wares -which, if not truly artistic, shall at least be inoffensive. Such a -mission is not to be accomplished without suffering. The man who essays -to attack a giant must be sure both of his ground and of his personal -condition. He who would establish his craft in the knowledge and -affection of men must possess enthusiasm, skill, discrimination and -infinite patience. - -It is not enough to discern the good, the hand must follow the brain -with diligent care. Furthermore, it is not enough to be able to make -things well, one must also make them good and know it. The -artist-artisan must have courage to destroy that which is below -standard, and self-denial to resist the temptation to sell an unworthy -product. - -The country needs craftsmen of this type and for them there is an -important work. For such, if they elect to join the ranks of the -potters, these words are written and in the hope that some may be -stimulated, encouraged, guided and helped the counsel of a fellow -craftsman is offered. - - - - -CHAPTER I: APPLIED ART - - -It is not intended, in these lines, to consider what are generally -termed the Fine Arts, painting and sculpture. These are perfectly -competent to take care of themselves and, indeed, the author can make no -claim to an ability to discuss them. In the field of applied art, -however, there are certain principles to be observed, principles, -moreover, which are frequently lost sight of because of the lamentable -separation of the functions of the artist and artificer. - -It is extremely difficult to draw the line between art and manufacture. -For example, a wall paper, designed with skill and executed by machinery -in actual reproduction of the work of the designer; is it a work of art -or is it a product of the factory? It is both. Primarily a work of art -is the product of the artist's own hand. It reveals his individuality. -It is the language in which he expresses himself to his audience. It is -the note of his voice. Such a work may or may not appeal to a large -section of the public. This will always be so. An artist, be he poet, -musician, painter or craftsman, is one who can see more than others. -What he sees he endeavors to express but it is inevitable that he be -sometimes misunderstood. Hence it the more necessary that his message be -delivered at first hand. To look upon a replica of the work of an artist -is like reading a sermon or an oration from a printed page. One may -gather much of the teaching but the personal note, the tone and gesture, -must be lost. - -But there are many who can gather the words of great men only from -books. There are, moreover, books which have never been spoken and -wherein alone the message is to be found. In like manner there are -works, emanating from the hand of great designers which can only be made -available for the many in a form of reproduction. The wall paper cited -as an illustration is of this class. Were it not for the printing press -this beautiful design could not have passed beyond the studio, and while -it is a great thing if a wealthy man can commission a Whistler to -decorate a peacock room, it is an advantage by no means to be ignored -that a well designed wall paper can be purchased by the piece. - -But while this is true of such of the household goods as cannot be -procured except by the medium of the machine, there are other examples. -In the case of the wall paper the function of the machine is simply to -transfer the proper design to the paper itself. This has no identity -except as a surface. It is no more to be considered than is a canvas -upon which a picture is painted. But when a chair or a table is formed -out of pieces of lumber uniformly shaped by one machine, the seat or top -put together by another and the legs or back carved or stamped by a -third, art or individuality is lost because mechanical construction is -involved. - -Still more is this the case in the product of the manufactory of -pottery. In commercial practice not only is a shape designed without -regard to decoration but the same decoration is placed upon several -forms, or a single form is made to suffer as the vehicle for many -decorations. Some of the results may be pleasing, even beautiful, but it -is more by luck than guidance and no piece produced in this way has any -claim to be classed as a work of art. - -On the other hand it may happen that a work of art, in the sense of -individual expression, may not even be beautiful and one is tempted to -ask the reason. If a work which is a genuine expression of a man's -personality fail to please the senses of those who are trained in the -finer perceptions there must be something wrong. - -If the adverse opinion be at all general amongst the critics it may be -assumed that they are right and that the worker is wrong. - -For example, the form of a flower is not a fit receptacle for a candle. -It often happens that a designer, struck with the beauty of, say, a -tulip, has modeled the flower in clay and made it into a candlestick. -Now it is obvious that the more closely the model simulates the flower -the less appropriate it is for such a purpose. If the model be heavy -enough to be of use it must be far removed from its prototype. If a -conventional design for a candlestick be adopted the petals of a flower -may be shown in relief upon it but there must always be a solid -foundation to account for the possibility of use. - -A favorite form with some designers is a bird's nest made into a flower -holder. In this the same criticism applies. A bird's nest is always -built to let water escape. Even a mud-lined nest is not impervious and -the idea is obviously inappropriate. It is important that imitation be -avoided and especially the imitation of material. One often hears the -remark "How beautiful, it looks just like bronze." This, of course, -comes from the casual observer to whom the skill of the imitation -appeals but it cannot be too strongly insisted upon that to imitate one -material in another is false from every point of view. Nor is it -necessary. Clay is sufficient in itself. There are so many effects -possible in pottery which are not possible in any other medium that it -is entirely superfluous to seek outlandish texture and color. To be -sure, such things are popular but that does not make them sound in -principle or true in taste. - -It should not be a purpose of any craft to make pieces merely as an -exhibition of skill. This is done sometimes by such versatile workers as -the Japanese, but it may be laid down as a law that a production of the -nature of a _tour-de-force_, an object which simply excites wonder at -the skill of the worker, is undignified and meretricious. It is akin to -the work of certain painters who delight in painting marble or velvet so -as to exhibit a perfect texture only and is but one degree removed from -the skill of the pavement artist who with colored chalk draws a lamb -chop or a banana in such a manner that the real article seems to be -lying on the ground at his feet. - -The true artist, be he potter or painter, works primarily for his own -satisfaction. It sometimes happens that a defect, not large enough to be -obvious, is a temptation to concealment. The public will never know. But -the consciousness of the existence of such a blemish will destroy the -pride of achievement which should accompany every finished piece. - -If the worker aims to draw any expression of opinion from the untrained -observer it should be in the nature of a remark on how easy the work -looks. Art will always conceal effort. Just as the poet or orator is at -his best when he clothes sublime thought in simple words so the artist -or craftsman glorifies his vocation when he makes use of means which -appear to be within the reach of every observer. - -In addition to the work of the producer there must be considered the -function of the critic. Artists are commonly impatient of criticism. -Tennyson voiced this sentiment when he wrote of "Irresponsible indolent -reviewers," but the power of the critic is rarer than the skill of the -craftsman. True, there are critics and critics. There is the man who -knows what he likes and who cannot be persuaded that he likes what is -false, and there is the trained critic who sees with an educated eye and -dissects with an unerring word. It is not common to find critic and -craftsman in one and the same person and it not infrequently happens -that the persons exercising these functions are at variance with each -other. - -But if the critic be correct why is the craftsman wrong? In this let it -be presumed that there is nothing wrong with his craft as such; that he -handles his tools skilfully and has perfect control over his material. -More than this, however, is necessary. The first requirement is a sense -of form, a term which includes outline, proportion and structure. Often -and often it is found that a designer depends upon novelty alone for -acceptance. He is not altogether to blame in this for the great American -public will, more often than not, ask, "Is it new?" - -Novelty in itself is no claim to consideration; in fact, on being shown -some product of which it is said "Nothing like it has ever been seen -before," the temptation is great to respond, "May its like never be seen -again." Novelty apart, form must possess proportion, balance and grace. -A chair must invite the sitter, a vase must stand securely, a carpet -must lie flat. The absence of these things may evidence an individuality -on the part of the designer but it is art at the expense of truth. - -The second necessary condition is fitness which again is expressed in -several ways. A porcelain vase is required to be light, graceful and -refined. A piece of ruder pottery may be no less satisfactory if it -exhibit vigor, strength and solidity. A large pot for a growing tree is, -for these reasons, more appropriate in grès than in porcelain. Porcelain -is translucent but such a quality is of no advantage in the case of a -flower pot; the strength of a massive body is, however, demanded by the -circumstances of use and hence the unfitness of the one and the fitness -of the other. - -Another point of fitness is concerned in the correspondence between -size, form and weight. It often happens that one takes hold of a piece -of pottery and experiences a shock. The mind unconsciously forms an -estimate of what the weight will be but the piece does not respond. The -effort put forth in accordance with the appearance of the object either -lifts it suddenly into the air or fails to raise it from the table. The -artist critic takes note of these things. To handle his wares is a -constant pleasure, for one is not continually disappointed by unexpected -violences. This correspondence or equilibrium is apart from the use of a -piece of pottery. It is quite as legitimate to express one's ideas in -clay in the presentation of simple beauty as it is to express them with -paint upon canvas. At the same time there is always a satisfaction in a -vase or flower pot that it can be used if required. Thus a vase which -will not hold water is technically imperfect and the _bête noire_ of the -conscientious potter. - -It is in the harmony of these things that the rôle of the critic is seen -to advantage. If the artist be capable of criticizing his own work he is -in a position to command attention but he must either discipline himself -or be disciplined by others, which, after all, is the way of the world -at large. - - - - -CHAPTER II: POTTER - - -It must always be an open question how much credit for artistic feeling -can be given to primitive races. The production of pottery was, at -first, the supplying of a need. Clay offered a medium for the making of -household utensils which were at once fireproof and impervious. The work -does not belong strictly to the earliest stages of civilization but is a -development of advancing refinement.[A] - - [A] Those who wish to study Indian pottery in detail are referred to - Dr. W. H. Holmes' work on the Aboriginal Pottery of the Eastern - United States, published by the Smithsonian Institution, - Washington, D. C. - -Crude and unprepared clays were used for the most part but the makers -could scarcely have been conscious of the charming color-play produced -by the burning of a red clay in a smoky fire. The pottery of the Indians -is artistic in the sense of being an expression of an indigenous art and -much of it is beautiful, though whether the makers possessed any real -appreciation of beauty is open to doubt. - -The pottery was exclusively the work of the women. No wheel was employed -but the ware was mainly constructed by coiling. Long strips of clay were -rolled under the hands and made of uniform size and these were then -coiled in spiral form, the rolls being welded together with water. After -proceeding a certain height the walls of the growing jar would become -weak under their own weight. The piece would then be set aside to -undergo a partial hardening upon which the work would be carried forward -another stage. The shape being completed and partially dried, the maker -would work over the whole surface with stones or simple tools until the -marks of the coils had disappeared and the walls had reached a -sufficient thinness. A great deal of skill was exercised in -accomplishing this. - -Many of the Indian forms are transitional. The basket, the gourd and the -bark-made jar suggested their shapes to the potter; indeed it is -sometimes evident that clay vessels were constructed as linings to -wicker forms, the outer layer of twigs being afterwards burned off. The -firing was performed in the open flame without any protection, a fact -which accounts for the great irregularity found in quality and color. - -The decorations used by the Indian women were of the type common to -unglazed wares. The clay was incised or embossed and natural earths were -used as pigments. This accounts in great measure for the fitness which -may be observed in aboriginal decoration. There is an absence of -artificial coloring, nor is there any straining after effect, but -instead there is shown a sober strength and a sane expression of values -which would do credit to a modern designer. - -America is fortunate in possessing abundant relics of primitive times -but it cannot be doubted that in other lands similar work was done, -making allowance, of course, for the characteristic variations in -national traits. The potter's craft is of such a nature, using an -omnipresent material and requiring the minimum of tools, that almost -every nation on the globe has practiced it. In some it has never been -developed beyond the narrow limits of the stone age, in others it has -reached the utmost perfection of cultured skill. - -For perfection of quality in crude pottery, no ware has ever surpassed -that of Greece. It is not practicable here to deal with the numerous -branches and sub-branches of Greek pottery; let it suffice for the -present purpose to speak of only two main groups. In the first, the -background of the decoration was supplied by the tint of the bare clay; -in the second, this tint afforded the color of the decoration itself, -the background being covered with a black pigment. To speak briefly -these groups are known as black-figured and red-figured wares. - -The wheel was early adopted by the Grecian potters as a means of -producing form and although molds were sometimes used, the wheel was, to -all intents and purposes, the sole method of manufacture. Greek pottery -is once fired. Birch classes it as glazed terra cotta, but the glaze is -nothing more than the black pigment with which the decoration is carried -out. The uncolored part of the clay is not glazed but polished with a -hard tool. Probably some famous potters employed assistants either to -make the pieces or to decorate but it does not appear that there was any -reproduction, at least, during the best period. At first primitive ideas -prevailed. Geometric designs were succeeded by rhythmic friezes of -beasts and birds done in black. When the human figure made its -appearance the faces were all in profile with full-fronting eye while -the prominent details of feature and drapery were scratched with a sharp -point before burning. - -The change of method to red on black gave much wider scope for the -treatment of the human figure, rendered a fuller expression possible and -enlarged the power of pictorial action. Great skill in drawing was -manifested and details of both drapery and features were expressed with -great care by means of the brush. - -Such was the state of the art when the decadence set in and the work -fell into the hands of plagiarists and charlatans. Meretricious coloring -and gaudy ornament succeeded the refinement and restraint of the earlier -days and so the art perished. - -To the inventive power of the Romans the ceramic art owes more than one -novelty. It would appear that the desideratum of the early days was a -black ware. Homer in his hymn wrote: - -"Pay me my price, potters, and I will sing. Attend, O Pallas, and with -lifted arm protect their ovens, Let all their cups and sacred vessels -blacken well And baked with good success yield them Both fair renown and -profit." - -The Greeks accomplished this blackening by means of a pigment, the -Romans secured a similar result by a manipulation of the fire. - -It is well known that the oxide of iron which imparts to the clay a red -color will, if burned in what is known as a "reducing" fire, turn black. -This is accomplished by keeping the air supply at the lowest possible -point and the effect is heightened by the smoke which is partly absorbed -by the clay. This black ware is known as Upchurch pottery from the name -of a locality in England where large quantities have been found, but -numerous examples occur in Germany and, indeed, wherever the Roman hosts -encamped. - -A second type of pottery is called Castor ware and consists of a dark -clay upon which the decoration is traced in clay of a lighter color. The -decoration was applied as a slip or cream and hence was the forerunner -of the modern slip painting or _pâte-sur-pâte_. This ware is well worth -a study. The decorations consisted largely of conventional borders and -panels but it is specially notable on account of the free use of motives -drawn from daily life. One of the commonest scenes depicted is the hunt -of hare or stag, the animals and trees being often woven into an almost -conventional frieze. - -The most valued type of Roman pottery seems to have been the Aretine or -Samian ware. This is a bright red color and possesses an extremely thin -glaze. A particular clay was evidently used, but all knowledge of its -source has been lost. - -With the importation of Chinese porcelain by the Dutch the whole trend -of pottery manufacture was changed. No longer was black a desirable -color, white was seen to be much more delicate and beautiful and -henceforth the endeavor of the potter was to produce a ware which should -be as nearly like porcelain as possible. The crudeness of the clay kept -this ideal from being realized, but various expedients were adopted and -gradually better results were obtained. - -Throughout the East a type of white pottery was made which, though -stimulated by the Chinese example, may have been a relic of the -knowledge of the Egyptians. A crude clay was coated with a white -preparation, possibly ground quartz, and upon this there were painted -conventional designs in sombre colors. A clear glaze covered the whole -and imparted to the colors a beautiful quality as of pebbles under -water. The nature of the glaze is made evident by the hues assumed by -the metallic oxides employed as colorants. Copper oxide affords a -turquoise blue, manganese, a wine purple, and iron, a brick red. If the -glaze had contained any considerable amount of lead oxide, these colors -would have been quite different; copper would have produced green, -manganese, dark brown, and iron, yellowish brown. The iron pigment was -evidently a clay, sometimes spoken of as Armenian bole. The red color is -always in raised masses because if a thin wash had been used the color -would have yielded to the action of the glaze. - -This ware, commonly called Oriental _engobe_ ware, affords a fruitful -study. Effects similar in character were produced by the late Theodore -Deck of Paris, but no considerable use of the ancient methods has ever -been attempted. - -The use of tin and lead in glazing was known to the Arabian and Moorish -potters but these ingredients were not abundant in the East. When, -however, the Moorish hosts conquered a part of Spain in the twelfth -century it was found that both lead and tin were available. The result -was the development of the enameled ware known by the generic name -Maiolica. Some have maintained that this was first made in Italy but the -name is derived from the island of Maiorca from which much of the -pottery was exported. The famous Alhambra vase remains as a monument to -the skill of the Hispano-Moresque craftsmen, but it was the Italian -artists of the Renaissance who brought the enameled wares to perfection. -The interest here is artistic and technical rather than historical, but -no one can study the work of the period without learning something of -Luca della Robbia and Giorgio Andreoli, of Gubbio and Pesaro and Castel -Durante. - -The use of lead in the glaze proved seductive. It simplified the -technical problems and provided a brilliant surface but alas! the colors -suffered and one by one they succumbed. The blue of cobalt, however, -proved indestructible and so, when the technical knowledge of the South -met the traditions borrowed from the Chinese, there was born, in the -little town of Delft in Holland, the blue enameled ware which has ever -since been known by the name of its native place. - -As to the technical details of the production of Delft ware a great deal -of information is available. The clay used contained a goodly proportion -of lime and this served to hold the enamel in perfect union with the -body. The decoration was painted in cobalt blue upon the unburned -surface of the enamel. This was, in a measure, courting a difficulty but -it is the glory of the craft that a difficulty is cheerfully accepted if -in the overcoming there is found success. If the Delft potters had -burned their enamel in order to make the painting easy, the world would -never have enjoyed the tender tone of blue for which this pottery is -famous. By painting the blue color over the powdery enamel, a more -perfect union of enamel and color was accomplished than would have been -possible by any other means. This fact alone is sufficient to account -for the unsatisfactory nature of the modern, so-called, Delft. -Difficulties have been avoided rather than met and the success of the -early masters has eluded their recent followers. - -Much of the pottery made in France in the seventeenth century was -inspired by the Italian renaissance. In fact the word faience is due to -the avowed intention of the manufacturers of Nevers to copy the enameled -pottery of Faenza. Almost the only novelty of the time was the -inversion, by the Nevers potters, of the Delft idea. Instead of a white -enamel with a blue decoration they used, in part, a blue ground with a -decoration in white. It is not known that this variation found -acceptance in any other place but in many localities, notably at Rouen, -the manufacture of enameled wares was pursued with great success. The -only real difference between the wares of Spain, Italy and France, lies -in the decorative treatment. Sometimes the emphasis was laid upon -lustres, sometimes on blue and white and again upon polychrome painting. -In one place there was an extensive use made of pictorial treatment, in -another all was conventional. The differences are interesting to a -student or a collector but to the craftsman enameled pottery affords but -one, though by no means an unimportant, means of expression. - -France, however, gave birth to two important and interesting departures -from the beaten track; the so-called Henri deux ware, and the faience of -Bernard Palissy. Important as these are to the ceramist, it is a -remarkable fact that neither of them had any appreciable influence upon -the art as a whole nor did they leave any descendants. - -A good deal of controversy has raged around the pottery commonly known -as Henri II, some authorities claiming that it should be called Faience -d'Oiron, and others assigning to it the name Saint Porchaire. It was, -quite evidently, the production of an individual or group of individuals -who had no connection with ordinary pottery manufacture, and the small -quantity produced is evidence that it was made for personal pleasure. -The name Henri II is undoubtedly satisfactory, for it was made in the -reign of the second Henry and some pieces bear the monogram of the king. -On the other hand H may be the initial of Helene d'Hengest, who occupied -the chateau d'Oiron and who had in her employ one Bernard who filled the -position of librarian. The style of the work seems to indicate a -devotion to books, for the patterns are suggestive of book-binding tool -work but were not produced in the same way. The ware was made of a -natural cream-colored clay and the shapes were modeled with great skill. -Upon the plain surface patterns were tooled or incised and the hollows -thus formed were filled in with dark-colored clays. The whole was then -covered with a clear lead glaze which afforded a finish very much like -modern earthenware. - -The origin of this work is a matter of little more than academic -interest but the technical details are of such importance as to be well -worth a study. The ware is original and unique. No pottery either before -or since has approached it in method, and the quality of most of the -pieces is all that could be desired. Such was the elaboration of detail -that no price could have been set upon the ware and it was evidently not -made for sale. A distinct growth in style can be traced. The first -pieces were somewhat archaic and even crude but as skill was acquired -greater perfection was attained. As is too often the case, however, the -skillful hand overreached itself and the later pieces are loaded with -meretricious detail in many colors. There are only about fifty pieces -known and these are equally divided between the museums of France and -England. - -Bernard Palissy was a versatile genius but is here only considered as a -potter. He states in his records that he was inspired by seeing an -enameled cup. It was at one time supposed that this cup was of Italian -maiolica but later authorities incline to the belief that it was a piece -of Chinese porcelain which Palissy supposed to have been enameled. No -white clay was known to him but enameled wares were quite accessible. It -can scarcely be believed that maiolica was a novelty but it can easily -be understood that a piece of white porcelain, viewed in the light of -the contemporary knowledge of enamels, would appear of marvellous -quality. - -Palissy essayed to imitate this wonder but attacked the problem from the -standpoint of an opaque glaze. He spent fifteen years in experimenting -but never realized his ideal. He did, however, produce a palette of -marvellous colored enamels. He was a close student of nature and modeled -all kinds of natural objects, glazing them in the proper hues. He also -designed and made vases and service pieces, some with figure -embossments. The story of his struggles is readily accessible to any who -are interested. - -Palissy left little or no impression upon the ceramic art of his time -but in recent years some work has been done in colored glazes fusible at -a low temperature. This ware is sometimes sold under the name of -maiolica but it is more nearly an imitation of Palissy. The main -difference between the two types is that while the maiolica or -tin-glazed pottery of Spain, Italy and France consisted for the most -part of a white enameled surface upon which painting was applied, -Palissy used little or no white enamel but decorated his wares with -tinted glazes which themselves supplied the colors. - -In the low countries and the German states there was made the striking -and original pottery known as _Grès de Flandres_. The clay was of the -type commonly used for the manufacture of stone-ware and appears in -three colors, brown, gray and cream. The ware was made on the wheel and -embossments more or less elaborate were subsequently added. The unique -feature consisted in the method of applying the glaze. This was simply -common salt, thrown into the heated kiln and volatilized. The salt vapor -bathed the glowing pottery and combined with its substance, thus -producing the delightful orange-skin texture known as salt glaze. - -The knowledge of this method was conveyed to England in the seventeenth -century and gained wide acceptance there. The English potters preferred -to use clays which were almost white, and after glazing a decoration in -brilliant colors was sometimes added. Naturalistic treatment was not -attempted but conventionalized subjects were used with almost the effect -of jewelry. The temperature at which this work can be produced varies -with the clay. Many fusible clays will take a salt glaze but the beauty -of the product depends to a large extent upon the purity of the body. -This necessitates a hard fire, for white-burning clays always need a -high temperature for vitrification. The early potteries of England were -dependent largely upon clay effects. Some little enameled ware was made -and is known as English Delft; but the bulk of the work was slip -painted, incised, marbled or embossed. Each of these methods is capable -of an intelligent application and all are within the reach of the artist -potter. - - - - -CHAPTER III: PORCELAIN - - -The production of porcelain is the goal of the potter. The pure white of -the clay and the possibility of unlimited fire treatment exert a -profound influence upon the imagination while the difficulties of -manipulation only serve to stimulate the energy of the enthusiast. For -present purposes not much is to be learned from the soft porcelains of -France nor from the bone china of England. German and French hard -porcelain are but developments of the Chinese idea and therefore need -not be studied apart from their prototype. - -The earliest date of Chinese porcelain is unknown. The records of the -nation are very ancient but their meaning is often obscured by the fact -that in the Chinese language the same word was used of old to denote -both porcelain and earthenware. Specimens dating from only the tenth -century A. D. look almost incredibly old. They are coarse and heavy in -structure but are aglow with vibrant color. The finest porcelains date -from the fourteenth and fifteenth centuries and these are the ideals -towards which every modern potter looks. - -Broadly it may be stated that two methods prevailed. In the former the -glaze itself was charged with color or the coloring matter was applied -to the clay beneath the glaze. In the latter the porcelain was finished -as to body and glaze and the decoration was applied at a subsequent and -much lighter burn. - -The first named class is called single-colored porcelain; the second has -several names such as the famille rose and famille verte as defined by -Jacquemart. - -In the single-color class it is evident that the potters were not at all -sure of their results. In many museums there are to be found examples of -ox-blood red, more or less fine, and, with them, other pieces which were -intended to be red but which failed in the fire. The wonder is, in these -cases, that the pieces, even though failures, are beautiful. The -knowledge required for the production of these wares is largely -scientific; at the same time it is not to be believed that the Chinese -had any special scientific training. They evidently traveled a long and -tortuous path before the goal was reached, in fact, they often fell -short of it altogether, but they had plenty of time and unlimited -patience. The modern potter is, if less patient, more fortunate in that -the course has been marked out with more or less accuracy and, if the -landmarks of science be heeded, a certain degree of success may be -attained. - -This single-color work is the true field of the ceramist. Anyone -possessing the power of using a pencil, and with a large stock of -patience, may produce over-glaze decoration, but to prepare glazes of -many hues and to consign them unprotected to the fury of the furnace, -requires skill, patience, courage and enthusiasm. - -During the last twenty years a new school has arisen which combines in a -measure the advantages of the two Chinese methods. Colors are prepared -from refractory materials and upon clay or soft burned biscuit ware, -scenes, in more or less conventional form, are painted, or else a design -purely conventional in character is applied by the artist. The ware is -then glazed and subjected to the severe fire which all porcelain -undergoes. The result is that the porcelain and the painting are united -in a sense that can never be the case with over-glaze treatment. The -colors become part of a purely ceramic unit; the spirit of the artist is -fixed by the fire. - -To this class belong the porcelain of Copenhagen and the recent product -of Sevres. These, of course, represent the result of much arduous -training and many tedious experiments. Both the training and the -experiments are necessary to some extent for every worker, not only -because pottery clays vary much in composition, but because -individuality can only be obtained by the preparation, in the -laboratory, of the desired compounds. - -The Chinese, doubtless, stumbled upon many of their successes by -accident, helped by the fact that the character of the fire employed -influenced many of their colors. This will be explained in a later -chapter. They were, however, quick to seize upon that which was good. -Many fanciful names were given to the rarest colors, such as "the violet -of wild apples," "liquid dawn" and "the red of the bean blossom." This -idea has been carried further in France by the invention of such names -as "_Sang-de-boeuf_," "_Sang-de-poulet_," "_clair-de-lune_," etc., and -pursued in this country in "Peach blow." - -In the over-glaze treatment, the type named "famille verte" is -characterized by a clear green glaze or enamel over a design in black. -The whole is painted over the porcelain glaze and the green enamel is so -soft that it is often decomposed on the surface. When a broad black mass -is covered with green the decomposition gives rise to prismatic colors -and occasions the term "raven's wing black." Some of this ware has also -been gilt but the gold lines have disappeared and can only be located by -the slight dullness of the enamel where they once were. Well known to -collectors also are the rose-back plates. These belong to the "famille -rose" in which the characteristic note is a delicate rose pink. This -color is prepared from gold and when it is placed upon the back of an -egg-shell plate a tender rosy transparency is imparted to the piece. One -of the best known of the single colors is the pale sea green named -celadon by the French. This color in China was called "the sky after -rain" and was considered both rare and valuable. - -The porcelain of Copenhagen is the product of scientific skill and -artistic taste. In the studios attached to the Royal Manufactory there -has grown up a tradition of work and criticism which is fostered by -ladies of birth and position. Many of these paint upon the porcelain -themselves and so constitute a school which has become world famous. - -Natural objects are, for the most part, chosen and, as the palette of -colors is, owing to the intense fire, quite limited and low in key, a -tone of quiet atmosphere pervades the painting. This is accentuated by -the use of the air-brush to distribute a ground color upon the ware in -graduated strength. - -At the National Manufactory of Sevres there has been some attempt to -follow the Copenhagen method but to a greater extent the work is along -the lines of conventionalized form. In this treatment the French artists -excel, being wonderfully accurate--almost too accurate--in their lines -and spacing. Several individual workers in France have also pursued this -plan, designing and executing the pieces which have made the French -artist-potters famous. - -In the porcelains of Berlin the quality lies largely in the complete -mastery of technical details. The work is, as would be expected, German -in style, but the paste is pure and the colors are well prepared. - -From this brief review it will be seen that the interest in the -manufacture of porcelain lies not so much in variety as in the value of -individual results. In the pottery described in the previous chapter a -great many different clays were used and each one proved suggestive to -the potter. In porcelain, on the other hand, the body clay is almost -identical wherever prepared, the requirement of a white translucent -paste being paramount. - - - - -CHAPTER IV: THE NATURE AND PROPERTIES OF CLAY - - -Clay differs from earth or soil in that it possesses certain -characteristics which these do not possess. Its distribution is very -wide but for the most part it lies concealed from view. In certain parts -of the country it is so abundant that it breaks through the surface or -is exposed as an outcrop but usually it is covered by the soil which -supports vegetation. Unless the subsoil consists of sand it is easy to -expose a clay by plowing or digging with a spade. It usually appears as -a greenish or bluish substance of close and uniform structure. The -texture is sometimes smooth but more often numerous small stones are -found imbedded in the mass. Such clays as are commonly found can be used -for the manufacture of some kind of pottery but in the great majority of -cases the ware will be red when fired because the clay contains a -proportion of oxide of iron. A pure clay does not contain this and -therefore becomes white or nearly white in the kiln. - -Pure clay, known as clay base or clay substance forms a part of all -natural clays though sometimes only a small part. It consists of silica, -alumina and water in a state of combination and is thus known as a -hydrous aluminium silicate. While this substance is very common as an -ingredient of ordinary clay, it is rarely found alone or uncontaminated. -Commercial or workable clays may be said to consist of clay base and -sand, with or without other impurities such as lime and oxide of iron. -For working purposes it may be granted that the potter has to deal with -a mixture of clay and sand. But sand is not a definite expression. It -may vary both physically and chemically within wide limits. The physical -nature has to do with condition, the chemical with composition. Thus a -sand may be almost as coarse as gravel or as fine as the clay itself. It -may be a pure quartz sand or it may be a crushed rock of almost any -composition. The former is known as quartz, the latter as feldspar or -feldspathic sand because it approaches in composition the group of -minerals known as feldspars. Each of these ingredients, clay, quartz and -feldspar, has an important part to play in the transformation of clay -into pottery. Few of the clays used in making white pottery possess -these ingredients in the correct proportions so that it becomes -necessary to make a mixture in which the necessary proportions will be -found. - -For successful pottery making three properties are demanded in a clay. -First, plasticity. Without this, clay could not be shaped at all. It -constitutes the obedience of a clay to the forming influence whether -hand or mold. The necessity for this quality may be illustrated by the -proverb "Making ropes of sand" as an example of the impossible. Sand, -possessing no plasticity, cannot be shaped or made to hold together. - -The second property is porosity. A clay which exhibits a high degree of -plasticity can be easily shaped but it cannot be safely dried. The water -of plasticity cannot escape and therefore the clay warps and cracks. The -function of porosity is to prevent this. A porous clay permits the water -to escape freely and the clay can be dried without damage. This -condition is produced by the admixture of sand or by the presence of -sand in a natural clay. A coarse sand is more effective than a fine sand -but a sand that is too coarse will interfere with delicate working while -a sand that is too fine approximates the action of the clay itself and -produces a substance which is dense rather than porous. Porosity is -therefore the reverse of plasticity and these two properties must be -adjusted so as to balance each other. - -The third necessary property is commonly known as vitrification but -could be better named "densification" because complete vitrification is -not attained in ordinary clay wares. This property may be defined as -that which causes a clay to yield to the action of a high temperature so -that the result is a ware, more or less dense, which is hard, durable -and sonorous. With this there must be coupled a certain amount of -resistance to heat treatment so that the pottery does not fuse or -collapse during the firing. Here also is found the need for adjustment. -The clay must yield to the fire but not completely. It must resist but -not entirely. - -Plasticity is due to the clay base. Not only to its quantity but to its -quality also. Some forms of clay in which clay base predominates are not -plastic because the clay base itself is coarse grained. Other forms with -less clay base present are plastic because this ingredient is fine -grained and tough. Pure clay base is also highly resistant to fire and -therefore contributes to the refractoriness of the mass. - -Porosity is caused by the sand in the clay. Any kind of sand will -produce porosity but the effect differs with the condition of the sand. -Coarse sand is more effective than fine sand. More sand will, of course, -cause greater porosity. - -Vitrification or densification is due to the feldspar or fusible sand. -This also varies with the condition. A fine-grained feldspar will -produce vitrification more easily than the same amount of coarse -feldspar. - -Certain substances are available for use in pottery mixtures, which -possess one or other of the necessary properties in high degree so that -they will impart these properties to a mass to which they are added. - -Kaolin or china clay is usually fine, white, and refractory. Some -kaolins are rather plastic but most of them are "short" in working and -rather tender. For the production of a white ware kaolin is -indispensable. No other ingredient will afford the pure white color -which is sought after in porcelain and china. - -Ball clay is very plastic, easily vitrified, but is not white. The color -varies from a cream to a gray. The use of a ball clay is therefore -limited in white wares because it will spoil the color. For wares in -which a light cream color is not objectionable ball clays are valuable -and almost indispensable. - -Stoneware clay is usually a rather plastic clay which contains a good -deal of sand, hence stoneware clays can be used for certain classes of -ware without admixture. A rather high temperature is required for most -of these clays, though occasionally one can be found which will become -dense at the fire of a studio kiln. The clays sold by the Enfield -Pottery Company and by the Western Stoneware Company are of this type. - -Ground flint is a necessary ingredient in almost all pottery. It aids in -the porosity of the clay and enables the mixture to be adjusted to fit a -special glaze. - -Ground feldspar is also necessary. Like flint it aids in the porosity of -the unburned clay but unlike flint it produces density in the firing. - -By a proper adjustment of these ingredients a clay can be composed which -will meet the special requirements of the worker. - -In order to ascertain the properties of any given clay certain simple -tests may be made and every clay-worker should know how to do this -because one cannot be too well informed as to the materials to be used. - -First, water of plasticity. A certain portion of the clay, dried and -powdered, is weighed out. It is convenient to weigh in grams and to -measure in cubic centimeters because in this way calculation is easy. -The scales and weights are described in the chapter on glazes. For -measuring the water a glass vessel called a graduate is used. One -holding a hundred cubic centimeters and graduated in centimeters and -tenths can be obtained from a dealer in chemical supplies. One hundred -grams of clay is weighed out and transferred to a glass slab. The -graduate is filled with water to the one hundred mark. Some of this -water is then poured on to the clay, adding little by little as needed -until the whole can be worked into a stiff mass of the proper -plasticity. The quantity of water used is then carefully noted by -observing how much is left in the graduate. Suppose, for instance, 70 -cubic centimeters are found remaining, the hundred grams of clay has -absorbed thirty c.c. of water and as one c.c. of water weighs one gram -the clay has taken just 30 per cent. This amount is important because it -is one of the best indications of plasticity. A very plastic clay may -need 40 per cent, a non-plastic clay may be satisfied with 25 per cent. - -Second, shrinkage. The mass of plastic clay is now transferred to a -plaster bat and rolled or pressed out into a smooth slab about 12 -centimeters long. Here again the centimeter is used in preference to the -inch as being more easily calculated. A faint line is ruled on the clay -slab and two fine scratches are marked exactly ten centimeters apart. -The edges are trimmed and the excess clay made up into three or four -small pieces which are to be fired in different parts of the kiln as -tests for density. When the clay slab is dry the distance between the -marks is measured and noted. The ten centimeters being divided into one -hundred millimeters, each millimeter of shrinkage means one per cent. -After firing, a second measurement is made and the differences are noted -as dry shrinkage and fire shrinkage respectively. - -Third, firing. The slab with the measurement upon it is set in the kiln -in the place where the clay wares are to receive the first or biscuit -fire and the small pieces are arranged in different places so as to -secure as many different conditions as possible. The position of each -should be carefully recorded. After firing, the marks on the slab are -measured as already described and note is taken of any warping of the -piece. The color is also recorded. The small pieces should be tested for -porosity or absorption of water but this is rather a delicate operation -and needs a particularly sensitive balance. Generally it will suffice to -use a wet sponge or to dip each piece into water, removing it quickly -and noting carefully the rate of speed at which the water is absorbed. -If the water should be scarcely absorbed at all a line of ink may be -drawn upon the pottery with a pen, the piece being perfectly dry. In a -fully vitrified ware the ink can be washed off, leaving scarcely a mark -but the test is quite sensitive and with a little practice will afford -an excellent means of comparing the density of different clays or of the -same clay at different temperatures. - -Fourth, glazing. It is well to have ready a small supply of a standard -clear glaze. Each of the test pieces should be covered with this in a -rather thin coat and then they should all be fired again, this time -close together so that they will receive the same heat treatment. This -will enable one to determine what degree of fire for the clay will best -suit the glaze. - - - - -CHAPTER V: THE PREPARATION OF THE CLAY - - -A clay having been selected in accordance with the tests described, it -becomes necessary to prepare it for use. A fairly large supply should be -obtained and stored in a dry place. Most natural clays need some kind of -cleansing for there are almost always foreign substances present. This -cleansing is accomplished by reducing the clay to the fluid known as -slip. The necessary appliances for making slip are as follows: - - A large sieve of quarter-inch mesh. - - A small wire sieve of about 14 meshes to the inch. - - A large barrel. - - Two galvanized pails. - -The clay is, after drying, powdered and sifted through the large sieve. -One of the pails is half filled with clean water and the clay, handful -by handful, is sprinkled into it. The clay rapidly absorbs the water and -sinks to the bottom. The addition of clay is continued until a small -mound rises through the water, when the whole is left to soak for an -hour. The bared arm is then plunged into the pail and the mass stirred -vigorously. A stick or paddle will serve, of course, but the potter -learns a great deal by the feel of the clay and therefore the hand is -best. It is said that he is a poor sailor who will not dip his hands in -the tar bucket and in like manner, he is a poor potter who fears the -slip tub. This stirring will tell a good deal about the probable working -of the clay. It may be stony or sandy or greasy. The large stones and -roots will have been removed by the sieve but now, after thorough -mixing, the slip is poured through the small sieve into the barrel. Both -pails may be kept going at once, one being filled while the other is -soaking and so on until the barrel is full or, at least, a good quantity -of slip has been prepared. - -If the clay prove very sandy it should be washed. The mixture in the -pail having been well stirred is allowed to stand for a definite time, -say one minute. The slip is then poured into the second pail and it will -be found that a quantity of sand has settled. This is thrown away and -the slip in the second pail is examined. If enough sand has been -removed, the slip may be poured into the barrel, using the fine sieve as -already described. If still sandy the process should be repeated, the -settling being for two minutes. Experience is the best guide in this -operation but all the sand should not be removed. - -When the barrel is full of slip it is allowed to stand over night when -some inches of clear water will be found at the top. This is removed -with a siphon which may be made of a piece of lead or rubber pipe. The -removal of the water results in the thickening of the slip and the -contents of the barrel should be thoroughly stirred with a long wooden -paddle to insure a uniform consistency. If the slip is found to be still -thin another settling and removal of the water will thicken it. - -The slip thus prepared will keep indefinitely, provided that it is not -allowed to become dry by evaporation. It improves greatly with age. This -is the material which is used for casting as will be described later but -for plastic work it must be still further thickened. A shallow box may -be procured and made water-tight and the slip, when poured into it, will -thicken much more rapidly than in the barrel, but it is better to have -some shallow plaster dishes as the plaster itself absorbs the water and -thickens the clay. Instructions for making these dishes appear in the -chapter on plaster. - -These directions will suffice for the preparation of a natural clay but -it is sometimes desired to prepare a white body either of earthenware or -porcelain. These bodies do not exist in nature and therefore a mixture -must be made. The ingredients are kaolin or white porcelain clay, ball -clay or plastic potters' clay, ground quartz or flint, and ground -feldspar.[B] - - [B] Georgia Kaolin and Tennessee Ball Clay may be procured from the - John H. Sant and Sons Company, East Liverpool, Ohio, and flint and - feldspar from the Golding Sons' Company, Trenton, N. J., or the - Eureka Flint and Spar Company, Trenton, N. J., in quantities of not - less than one barrel or sack. - -A suitable mixture for earthenware is-- - - Georgia Clay[C] 20 parts by weight - Tennessee Ball Clay 30 " " " - Flint 35 " " " - Feldspar 15 " " " - --- - 100 - -and for porcelain-- - - Georgia Clay 45 parts by weight - Flint 35 " " " - Feldspar 20 " " " - --- - 100 - - [C] If English china clay can be procured it will make a whiter ware - than Georgia clay. - -The earthenware will be creamy in color and porous at an ordinary fire. -The porcelain will need a hard fire and will be white and translucent. -It is, however, non-plastic and hard to work. The preparation of these -mixtures of course necessitates a pair of scales but otherwise the -treatment of the mix is the same as that of natural clay. Washing is not -necessary but the clay must be powdered, mixed with the flint and spar, -and sprinkled into water as already described. In place of the wire -sieve, however, a silk lawn of 120 meshes to the inch should be used. - -The lawn is simply a fine sieve and is named because of the material -(also called bolting cloth), with which it is covered. Have a carpenter -make a box without a bottom. Cypress or oak should be used and this -should be a full half inch thick. Four strips of the same thickness are -also to be provided. The box may be of any convenient size; eight inches -square and four inches deep is about right. The sides should be fastened -together with brass screws to avoid rust and a piece of lawn is strained -tightly across the bottom and secured with copper or brass tacks. A -strip of coarse muslin folded and laid along the edges will help to -prevent the lawn from tearing, the tacks being, of course, driven -through both muslin and lawn. Then the four wooden strips are set upon -the muslin and secured with brass screws. The completed lawn is then a -tray of which the bottom is formed of lawn. The strips of wood beneath -serve to protect the lawn when placed on a table as well as to assist in -holding it firmly.[D] - - [D] Silk lawn of any desired mesh may be purchased by the yard from A. - Sartorius & Company, 57 Murray Street, New York City; or brass - sieves ready for use from the W. S. Tyler Company, Cleveland, O. - -For storing clay in the plastic state there is nothing better than -stoneware jars. These may be had of any size and a tinman should make -close-fitting covers. Earthenware covers do not fit tight and are always -getting broken. A little water is poured into each jar and a support -provided for the clay so that it does not rest in contact with the -water. Under any conditions clay will slowly harden so that not too -large a stock should be kept. Slip, on the other hand, keeps well so -long as some water is always on the top and it is not a long process to -stiffen it into clay. - - - - -CHAPTER VI: MOLD-MAKING AND PLASTER - - -Plaster is almost a necessity to the potter and therefore something -should be learned about it. Even if one does not use molds there are -numberless purposes for which plaster is convenient. For stiffening slip -into clay, and for absorbing water from glazes, shallow dishes of -plaster are used, and for holding work either in making or drying, -plaster bats or round slabs are always in demand. - -It is best to purchase the finest quality of potters' plaster by the -barrel.[E] It will keep indefinitely if stored in a dry place. The -necessary appliances are: - - One or two large jugs for mixing, or a metal can with a spout. - - A metal spider or frying pan. - - Six feet of rubber machine belting, six inches wide, or similar strips - cut from linoleum or enameled cloth. - - Two or three thin pieces of steel of various degrees of flexibility - (scrapers). - - Handy knives, called vegetable knives. - - A small painter's brush. - - Two or three fine sponges. - - [E] Calvin Tomkins, 30 Church Street, New York City. - -To begin with, a size of soft soap and water is prepared. Put a quart of -water into a kettle and add a piece of soap the size of an egg.[F] -Simmer for an hour or until the soap is entirely dissolved and then set -aside to cool. When cold the size should be of the consistency of maple -syrup. This size is used whenever plaster is to be kept from sticking to -a form or surface, and it has also the merit of causing clay to stick to -plaster. For example, if a mold is to be taken from a clay model no size -should be used, but if a plaster form is used as a foundation for clay -ornament it should be well sized first. The size is laid on with a brush -and wiped off with a sponge. Another sponge is then used with clean -water and the sized surface is washed, all superfluous water being -removed. Size is then applied a second time and washed off as before. A -third application is sometimes necessary, or until the sized surface -rejects water like grease does. On the last sizing, water is not -applied, but the surface is polished with the sponge containing size. If -the surface to be prepared be of wood or metal a single coat of size -will often suffice, but if it be of plaster three or four applications -are often necessary. - - [F] Any good laundry soap will serve, but it should be sliced thin. - -The first lesson may well be the manufacture of a plaster bat. The -frying pan is first sized and set upon a level table. Let us suppose -that a quart of water will fill it to about an inch in depth. This -amount of water is put into a jug and two pounds and three-quarters of -dry plaster is weighed out and allowed to trickle through the fingers -into the water. This proportion has been found to be best for ordinary -mixings. A smaller quantity of plaster to the quart of water will result -in a very soft bat; a larger quantity will be proportionately harder. -After the plaster has soaked up all the water it will take, that is in -about two minutes' time, the hand is plunged in and the whole stirred to -a smooth cream. All lumps must be broken up and the air bubbles removed -as far as possible. Continue stirring gently and presently the mixture -will be felt to grow thicker. The psychological moment arrives when the -plaster forms upon the hand a white coating which cannot be shaken off. -The creamy liquid is then poured into the frying pan which is gently -shaken to level the surface. - -If the plaster has been poured at the right moment it will set smoothly -with a mat surface like sugar icing. If poured too late it will be stiff -and difficult to level, and if poured too soon it will curdle on the -surface and water will be seen above the plaster. A little practice will -show the right moment. The jug should be washed out immediately while -the plaster is soft. In the place used for plaster work a tub should be -provided in which all vessels and tools can be washed, for, if allowed -to flow down the waste pipe of a sink, the plaster will speedily choke -the outflow. - -After standing for some ten minutes, more or less, the bat in the frying -pan will grow warm. This is the sign of a combination between the -plaster and the water and shows the completion of the setting. The pan -is now taken by the handle and, holding it upside down, the edge is -rapped smartly on a brick or stone. This will cause the contents to fall -out and there is a smooth disc which is one of the most useful of -appliances. The edge will need to be scraped and the bat can be set -aside until needed. It will be good practice to make a half dozen of -these. - -This process of mixing and pouring plaster is the same for all -operations and the instructions will not be repeated, but when the -student is told to "pour plaster" it will be presumed that this -experiment has already been made. - -[Illustration: Fig. 1. _A_, table. _B_, clay mound. _C_, plaster. _D_, -rubber belt.] - -The next step is the making of a plaster bowl or dish for the purpose of -drying out slip or glaze. A convenient size should be determined upon as -it is best to have all the dishes the same. Upon any flat, smooth -surface a mound of clay is reared which shall be the size and depth of -the inside of the proposed dish. About twelve inches in diameter and -three inches deep is a good size, though fourteen inches is not too -large for the former dimension. This mound should be made as nearly -circular as possible and the clay finished as smoothly as may be. The -rubber belt is then set around the mound in the form of a hoop leaving a -space of two inches between the clay mound and the rubber hoop. The -rubber is fastened either by tying with string or by binding the -overlapping ends with clothes pins. A roll of soft clay is laid down -where the belt joins the table and pressed down outside to prevent -leakage. Enough plaster to fill the space within the belt is now mixed -and poured, covering the clay mound to a depth of at least one inch. -When the plaster has set the rubber is detached, the whole turned over -and the clay dug out. We have now a circular plaster dish three inches -deep but we have only one. The trouble of rebuilding the clay is -unnecessary a second time because a "case" or reverse can be made from -which as many dishes as may be necessary can be formed. - -[Illustration: Fig. 2. _C_, plaster dish. _D_, rubber belt. _E_, plaster -case or reverse.] - -[Illustration: Fig. 3. Plaster case, with rubber belt, arranged for -pouring.] - -The dish is carefully smoothed and trimmed. The sharp edge is removed -and the inside is dressed with fine sandpaper to a perfectly smooth -surface. Size is now applied to the inside and upper edge until a bright -slippery surface is obtained. The rubber belt is now bound closely -around the dish and plaster is poured to a depth of about one and -one-half inches on the edge. This, of course, makes a depth of four and -one-half inches in the center. When this new plaster has set in turn the -rubber is removed and the two castings can be easily separated by -inserting a knife at the junction. The knife should be gently driven in -with a hammer. Obviously it is now possible to make a number of dishes -from the reverse thus obtained, by simply binding the rubber belt around -each time and pouring plaster as at first. The original mold having been -sized is no longer absorbent but must be kept in case additional -reverses are needed. The molds or dishes must be thoroughly dried out -before being used. - -The molding of a vase form is more elaborate but not really difficult. -Even if one does not intend to produce pottery by molding there is -always an advantage in having a number of simple forms upon which to -make experiments. - -The vase to be molded is first drawn to exact size upon paper and a -plaster model is turned on a lathe. This can be done equally well on the -potters' wheel and the method is as follows: A plaster bat is saturated -with water and set upon the wheel so as to run true when the wheel is -revolved, and is cemented to the wheel head by a little slip. A few deep -scratches are made on the face of the bat and a cylinder, either of the -rubber belt or of stiff paper, is rolled up and set on end in the center -of the bat. The size of the cylinder should be a little larger every way -than the proposed vase. Plaster is now mixed and poured to fill the -cylinder. It will adhere to the bat below by reason of the scratches. -When the plaster has set, the cylinder is unfastened and removed and the -turning may begin. To turn plaster well involves a good deal of practice -but it is better to spoil three or four plaster cores in the learning -than to spend a long time on one for fear of damaging it. - -[Illustration: Fig. 4. Turning tools for plaster.] - -[Illustration: Fig. 5. Position of tool in turning. _A_, correct. _B_ -and _C_, incorrect.] - -The board support and turning stick described on page 100 are used in -turning plaster as well as clay. The turning stick is held in the left -hand and the point is pressed into the board. All this is, of course, -made ready before the plaster is poured. The turning tools are here -illustrated. They are not sold in the stores but can be made by any -machinist. The head or cutting blade consists of a flat piece of steel -through the center of which is a shaft or pin which is driven into a -handle. The head may be of any shape but the triangle and the circle -will meet every need. The tool is held in right hand and braced against -the turning stick, the stick and tool being moved together by raising or -lowering the left hand which holds the butt of the stick. - -While the plaster is still soft the round tool is used and the rough -form is rapidly turned. Then as the setting of the plaster proceeds and -it is found to grow harder, the triangle tool should be used and the -shape gradually wrought out with the point. Finally by using the circle -tool for concave lines and an edge of the triangle tool for convex lines -the form is perfected. The surface is to be finished and the tool marks -removed by using, free hand, a flexible scraper which is bent by the -fingers and thumb to fit the lines of the form, and a final smoothing is -given by fine sandpaper, the wheel being revolved all the time. At the -top of the form a small cylindrical piece is left, called the "spare" -which represents the thickness of the mold substance, and for the bottom -a small piece is turned in the shape of a truncated cone. The small end -of this should be the same diameter as the base of the vase. These are -shown in the illustration (Fig. 6). - -[Illustration: Fig. 6. Vase with foot piece and template. _A_, vase. -_B_, spare. _C_, foot piece. _D D_, templates. _N N N N_, natches.] - -It will be obvious that in the directions given above the base of the -vase is not finished off and therefore the form must be cut off from the -bat, either by a knife or saw, and the base is then finished by hand, or -by setting the form upside down in a clay cradle--called a "chum"--and -turning the base true. The form is now ready for molding. - -[Illustration: Fig. 7. End plates for mold. _E_, upper plate. _E'_, -lower plate. _N N_, natches.] - -The plaster vase is laid upon its side on a piece of soft clay and a -thin bat or plaster slab is cut to fit the outline. This template should -fit with reasonable accuracy but need not be absolutely exact. A pair of -these will be required, one to fit each side of the form. These slabs or -sheets of plaster are always useful and if a sheet of glass is kept -handy any excess of plaster left from a mixing may be poured on to it. -This upon setting is easily detached and will present a smooth face -where it has rested on the glass. The pair of templates must include, in -their outline, both the spare and the foot piece but should not extend -beyond either of these. The outside diameter of the mold is now to be -determined and the templates cut to this dimension so that the two -together, with the vase between them, constitute a longitudinal section -of the mold. - -The vase must now be divided accurately into two halves by a line -running from top to bottom. There are several ways of doing this. While -the form is still on the bat a diameter of the bat may be drawn and a -perpendicular erected from each end of this diameter. These -perpendicular lines will, of course, mark the center of the vase on each -side; or after the vase has been cut off another method is possible. -With a pair of dividers find the center of both the top and the bottom -of the vase. Mark each with a small hole or the point of a pencil. Now -lay the vase on its side on the clay cradle upon a glass sheet or other -level surface and raise or depress one end until the two centers are -exactly the same height from the glass. Take this height in the dividers -and, sliding one of the compass legs along the glass, gently scratch the -plaster vase with the other or upper point. If the two centers have been -accurately adjusted this scratch line will be the exact center of the -form. - -Some soft clay is now built up on each side of the vase and the -templates are pressed down upon it, one on each side until the upper -face of each corresponds with the scratched line. The vase is now seen -to be buried as to one half in a plaster surface, and plaster poured on -this will give a half mold. There is yet, however, nothing to confine -the plaster and it would flow away as fast as poured. Two end plates are -necessary and these must rise in a half circle above the bed formed by -the templates. The part below may be of any shape but must be high -enough to cause the diameter of the half circle to coincide with the -plane of the templates. Two pieces of cardboard, wood, or rubber belt -are now bound to the sides, the apertures at the top and bottom, caused -by the curve of the end plates, are stopped with clay and the whole -presents the appearance of a vase, only half of which is visible, lying -in a shallow trough. All the fitting should be carefully done but the -tying up is not yet. The whole is now taken apart and well sized. Vase, -foot piece, templates and end pieces are all to be sized thoroughly in -the manner described. They are then put together again and bound around -with twine. It is necessary now to make provision for the proper fitting -of the halves of the mold. This is done by providing knobs and hollows -which fit together. These are technically known as "natches" and will be -referred to as such. Take two pieces of moderately stiff clay each about -the size of a cherry. Roll them into neat balls and cut them in two with -a thin knife. Lay each of the halves, flat side down, upon the -templates, two on each, placing them in pairs opposite to each other. -Affix two or more of these on the inner face of the bottom end plate. -Now mix and pour the plaster. This should be poured to the height of the -top of the end plates and, after pouring, shake this well down by -dipping the fingers into it, so that no bubbles may cling to the -surfaces below. As soon as the plaster has become firm but while it is -still soft remove the string and the side boards, pull off the pieces of -clay and with a straight, thin piece of wood scrape off the surplus of -plaster by following the line of the end plates and thus making a half -cylinder. - -As soon as the plaster has become warm the whole may be turned over and -the templates and end plates removed. The four half spheres of clay will -be found embedded in the face of the plaster and these, being removed, -will leave four hemispherical depressions. The vase can now be gently -detached from its bed and the first half of the mold is completed. A -little dressing will be necessary. All overhanging edges and rough -places should be finished off and the hollow natches smoothed with a -piece of muslin on the end of a finger. - -The second half is simple. Replace the vase in the half mold, set the -foot piece in its place, replace the end plates with the diameter on the -line as before but with the semi-circular edges upward, and set two or -three clay natches on the bottom one. Size, bind up, pour and scrape off -as before, thus completing the two halves of the mold in cylindrical -form. It only now remains to make the bottom for, at present, the mold -is open at both ends. - -The two halves with the vase inside are bound very tightly together with -twine and set on the table bottom upwards. The clay natches in the -bottom are taken out and the hollows smoothed. The foot piece is taken -out and the rough places dressed. The bottom end of the vase is now -visible and this, together with the end of the mold, is sized. A strip -of stout paper is bound around the mold, projecting about an inch above -the end and plaster is poured to fill it. When this is set the paper is -peeled off and the edges of the mold are dressed smooth. The bottom may -now be detached by inserting a thin knife at the junction, the mold -opened and the form taken out. The mold is now in three parts which may -be put together at will and used for casting the vase in clay. - - - - -CHAPTER VII: CASES AND WORKING MOLDS - - -The mold described in the previous chapter is called, technically, a -"block mold" and is not, as a rule, used for making the clay ware. The -reason for this is that molds will wear out more or less rapidly and to -repeat the process of making new ones from the original form would be -tedious and expensive. - -From the block mold a reverse is made, called a "case," and from this, -in turn, working molds are made in any required number. While it is -possible to use the block mold as a working mold, and, if only a few -pieces are required this is quite sufficient, yet, as it is often -necessary to have a number of molds, the student should understand how -to make a case. - -A case may be defined as a mold from which a mold is made. If one can -imagine the visible half of the vase form as it appears in making the -mold, with the templates and ends cemented into one piece, one has a -conception of one half of a case. The problem is to make this with -permanent but movable ends so as to have a convenient form from which -half molds may be easily made. - -[Illustration: Fig. 8. Offset plates. _F_, top plate, front view. _F'_, -side view. _G G'_, bottom plate.] - -[Illustration: Fig. 9. Sectional view of mold ready for casing. _A_, -mold. _B B_, offset plates. _C C_, end plates. _N N_, natches.] - -The ends are joined to the body by means of offsets and the first step -is the construction of these. One half of the block is taken and laid -upon its back, being supported by clay so that the face is level and -steady. An offset plate is now cut to fit each end. To make these a -piece of plaster is selected or made which is true and smooth on both -sides. The plates are cut of the same width as the mold and are beveled -at the upper edge so as to rise slightly from the mold face. The curve -at the end of the mold is cut out to fit and beveled in like manner. -Then two end plates are fitted. These should be about two inches higher -than the offset plates and are square at the top. Upon each of these two -or three clay natches are set, being placed low down near the face of -the mold. The mold and plates are well sized and bound together with -side walls just as in the making of the mold. Plaster is poured to a -height sufficient to well cover the natches and left to set hard. No -shaping is necessary. When well set the end plates and offset plates are -removed but the vase mold and the case are left attached together. The -other half of the mold is prepared and run in the same way, the same -offset plates and end plates being used with such slight refitting as -may be necessary. The work is now examined and all rough places and -scraps of adhering plaster are removed. The two halves of the case, the -half molds being still attached, are set up on end, back to back, being -separated by a thin piece of plaster or a strip of cardboard which -should extend two inches above the top. The top ends are now sized, the -natch holes having been smoothed off, a band of paper is tied around and -plaster poured on top to a depth of about one inch. When set the whole -is turned over and the operation is repeated on the other end. After the -final setting the ends are easily removed and by the insertion of a thin -knife driven by a light blow, the molds and case are separated. Each -half case is now laid on its back and the proper ends are fitted in -place. It only now needs the usual side walls to be tied on and molds -can be made with ease just as the original block mold was made. - -[Illustration: Fig. 10. Mold and case in position. The top ends are -lifted to show fitting. The bottom ends are not shown.] - -It now remains to make a case of the bottom mold. The bottom piece of -the block mold is taken and sized and with a strip of paper bound around -it, plaster is poured. The two are detached when set and the case is -finished. It consists of seven pieces; three are used in each half and -one for the bottom. - -[Illustration: Fig. 11. Block of plaster with face of plate turned. _B_, -height of plaster to be poured. _C_, rubber belt.] - -Thus equipped it is possible to make any number of working molds and if -the case should wear out or be damaged, a new one can always be made -from the block mold. The block mold itself, having been sized, is no -longer absorbent and cannot be used for making vases. The working molds -should be thoroughly dried before using and they will last longer. - -Flat ware, such as plates and saucers, is made on, not in, a mold. The -diameter of the plate having been decided upon, a block of plaster three -inches wider is run. This is placed on the center of the wheel or jigger -and in it the face of the plate is turned. This must be sunk below the -level of the block and when finished, must appear as though the plate -itself were embedded in the plaster. One half of the thickness of the -edge is shown in such a way that there is no under cutting. Just outside -of this edge the plaster is turned so as to slope gently up to the level -of the block. - -Without removing the block from the wheel the face of the plate is well -sized, a band of belting is arranged, of the same diameter as the edge -of the slope and plaster is poured to a depth of three inches. Out of -this the back of the mold is turned as shown in the illustration (Fig. -12). - -[Illustration: Fig. 12. _A_, block of plaster. _B_, mold poured on face -of plate and turned.] - -The top of this as it lies upside down is shaped with a straight, almost -upright slope which enables the mold to be set securely in the wheel -head. Around the exposed edge of the original block, three or four -natches are now bored or cut. They should be placed at irregular -distances so that there will be no doubt as to the putting together of -the sides of the case. If two circular pieces of plaster have to be set -together and held by natches there should always be either this -irregular spacing or some distinctive mark, because if this be not -provided for, two or three trials will always be made before the correct -fitting is found and these trials wear out the natches very quickly. - -[Illustration: Fig. 13. _A_, bottom of case. _B_, Cavity for pouring -molds. _C_, top of case.] - -The back of the plate mold and the edges of the block are now sized and -plaster is run to the level of the highest part of the mold but no -higher (Fig. 13). When this is set, the two halves of the case can be -separated and the mold taken out. Now when the halves of the case are -fitted together there will be a cavity the exact size of the mold. This -can be filled again and again with plaster, a new mold being formed each -time. - -[Illustration: Fig. 14. Iron prong to fit wheel head.] - -[Illustration: Fig. 15. _A_, plaster, with prong inserted. _B_, rubber -belt.] - -In order to use these molds a special head must be provided for the -wheel. The regular head of the wheel should be detachable and in its -place an iron frame called a prong is fitted. This consists of a collar -either with a hollow cone or a screw to fit the shaft of the wheel, and -from this radiate four short arms. In order to use this a circular block -of plaster some two or three inches thick is poured on a table or slab -and just as this is setting, the prong, upside down, is pressed into it -just below the surface and held there until the plaster is hard enough -to support the weight of the iron. When hard, the whole is lifted and -the prong with the plaster attached is set in position on the wheel. -This now forms a rough plaster head and it must be turned true. In this -head a circular depression is to be turned which will exactly fit the -back of the plate molds. If the recess should wear larger as it will if -much used, a new head can easily be run. The same principle can be -applied to the making of molds for saucers. - -[Illustration: Fig. 16. Wheel head with plate mold. The tool used is -shown in dotted outline.] - -Cups and bowls are molded from the outside. A block of plaster about one -inch thicker than the height of the proposed cup is taken and centered -upon the wheel. Out of this the piece is to be turned, upside down, -leaving a ledge or platform, the outside diameter of which is the size -of the mold. The rubber belt is tied around this and the mold poured. If -for casting this will suffice, but if it is intended to make the cups -upon the wheel the outside of the mold must be turned to fit a -wheel-head which is hollowed to receive it. The making of the cups is -described in Chapter XI. A bowl is simply an enlarged cup. - - - - -CHAPTER VIII: BUILDING BY HAND - - -The production of pottery by hand is a form of modeling but with the -important difference that while pieces modeled by art-school methods are -not intended to be preserved in the clay itself, built pieces are -destined for the fire. It is therefore necessary not only that a special -clay be used but that the work be such as will hold under the strain of -the burn. The composition of the clay has been dealt with in another -chapter and it is presumed that the worker has decided upon the proper -mix or has procured a suitable clay. - -There are two possible treatments of built pottery; the work may be -finished by fingers and tools only or it may be placed upon the wheel -and turned to a true surface. In the latter case the result is much the -same as if the piece were thrown on the wheel as will be described. The -principal point of difference is that while building needs less practice -than throwing, turning a built piece is much more difficult and tedious -than turning a thrown one. It is almost impossible to build with -sufficient accuracy for the work to run true, and a great deal of time -is consumed in filling hollows and removing lumps. These do not appear -obtrusive when the work is held in the hand, but if it be revolved upon -a fixed center every slight irregularity appears to be accentuated. On -the other hand the charm of built ware lies in the subtle plastic -quality which belongs to no other material or method. - -For very large pieces such as tree pots the combination method is useful -but these should be built on the wheel itself and kept true as the work -proceeds. Then a slight turning at the finish, when the clay is leather -hard, will produce a satisfactory result. - -The clay for building should be rather soft as it is apt to dry quickly -on handling. The work may be done either with coils or pieces. - -A plaster bat should be made with a low dome in the center. This bat may -either fit the wheel or not, depending upon the plan adopted. The dome -is to raise up the bottom of the vase and form a foot. The table may be -covered with a piece of oil cloth or may be kept slightly damp. The -first attempt should be to build a cylinder as this form is easy to -construct and to keep true, so that the attention may be devoted to the -manipulation of the clay. - -It is first necessary to roll out the clay into cords which should be a -little thicker than the proposed walls are to be. These cords should be -as uniform as possible and should be rolled quickly to avoid undue -hardening. It is best to roll them as required. The domed bat is made -quite damp and upon it should be marked the diameter of the cylinder to -be built. A roll of clay is taken, one end laid in the center of the bat -and the rest is coiled around it in a spiral line. When the disc so -formed has reached the proper size, the coils are gently rubbed over -with the fingers until they have thoroughly united and the lines of the -spiral have disappeared. The clay disc may now be turned over and the -rubbing continued on the other side. The circle is cut true and a new -coil is laid on the outer edge thus making a shallow circular tray. In -raising the walls it is best to pinch off the roll of clay when one -circle has been completed and the new roll should be begun at another -point so that all the joints will not be at the same place. This plan is -better than coiling a long roll in a spiral for in this case one side of -the piece will be higher than the other. - -After three rolls have been laid in position the wall, both inside and -out, should be worked like the bottom so that the rolls will disappear -and the clay be welded uniformly together. This should be done without -water or with as little as possible. The use of water is very tempting. -It makes the clay so smooth and seems to help but it will inevitably -make the work sloppy and will tend to soften the walls. - -After three or four rolls have been worked in, the piece should be laid -aside for some hours to stiffen. If this be not done the weight of the -second building will cause the work to sag and fall out of shape. For -this reason it is well to have two or three pieces in hand at once so -that there need be no waiting. When the cylinder is of sufficient height -it should be allowed to become quite stiff and then the irregularities -should be corrected with a little soft clay which is worked into the -joints. The whole surface may now be gone over with tools and brought to -the required finish. As soon as the clay is hard enough it should be -removed from the damp bat and placed upon a dry one to become dry. - -In the method of building by pieces no rolls are prepared but the clay -is taken, pinch by pinch, each morsel being pressed into place as the -work goes on. This plan is somewhat more plastic in effect and is well -adapted to free-hand work; the resulting pottery, however, is generally -thicker and heavier. - -The craft of building is not mastered until the lines of a drawing can -be successfully followed. The clay is apt to choose its own way and the -result will be very different from what the potter intended. The design -should be carefully worked out on paper, full size if possible, and the -clay form should be compared with the drawing as the building goes on. A -profile may be cut in cardboard and this, applied to the clay from time -to time, will verify the line, but all such mechanical aids should be -used sparingly as the value of this work depends largely upon the sense -of freedom and self-expression which belongs to it. - -The thickness of the clay walls is a matter of great importance. A small -piece should not be so thick as to feel clumsy and heavy, nor should a -large piece be so thin as to lose the sense of strength and solidity. - -It may be found on drying the ware, that cracks, especially in the -bottom, are developed. The cause of this may be in the clay. A clay -which is too plastic or too fine in the grain will surely crack. Such a -clay may be opened or meagered by the addition of ground flint or fine -grog. The cause may, on the other hand, be in the building. If the -welding of the coils or pieces be imperfectly done, cracks are sure to -result. If the bottom be too thick it will crack. A great strain is put -upon the bottom in drying. The clay must be able to shrink and while the -side walls are able to settle down on themselves, the bottom is pulled -in every direction by the sides. The bottom should be made quite thin in -the center and thicker toward the edges. This will help to avoid cracks. -A bad crack cannot be successfully mended. It is best to break the piece -and begin again. To burn it means the loss of the clay but the clay will -be saved if the damaged work be withheld from the kiln. A small crack on -the edge is also hopeless. A crack showing on the edge of a piece is a -bad fault. A small crack in the bottom may be mended by dampening the -place carefully and pressing in a little stiff clay. - - - - -CHAPTER IX: THE POTTER'S WHEEL - - -Much of the glamour of the potter's art is associated with the wheel. -Poets have sung its praise and artists have delighted in its rhythmic -motion, but alas! the wheel as a commercial method of manufacture is -doomed to extinction. It cannot compete with the precision and speed of -machinery. It devolves, therefore, upon the artist potter to maintain -the wheel in its rightful place as, _par excellence_, the potter's tool. - -No clay worker's studio should be without a wheel, but the particular -form of wheel depends upon the nature of the circumstances under which -it is to be employed. - -The simplest wheel is that used by the Chinese. A circular plate with a -heavy rim is set upon a spindle so that it will revolve freely and run -steadily. As the workman sits or kneels upon the floor the surface of -the wheel is about at the floor level. Around the periphery and upon the -upper surface four holes are sunk and the workman, inserting a short -stick into one of these, gives the wheel a rapid motion. Then while it -is revolving by its own momentum the clay is centered and shaped. As the -motion is lost the stick is again inserted and the wheel spun. This -method, of course, involves much skill on the part of the workman. - -In the next form, one which is only adapted, however, for crude -experimental work, the wheel is set upon the frame of a sewing machine -and operated by the treadle. A beginning may be made upon such a wheel -but the operator will soon wish for something better. - -A common factory form and one which is well adapted for studio work is -the kick wheel. The wheel head is set at the top of a spindle and in the -upright shaft there is a crank to which is attached a horizontal moving -treadle. This is worked continuously by the left foot, the weight of the -body being supported by the right. The action is strenuous and scarcely -fitted for persons of other than robust physique but it can be used -successfully after practice. This wheel is made by the manufacturers of -potter's machinery. - -Another form of the kick wheel is used in Europe and is, in fact, the -original wheel used by the French and German potters in the seventeenth -century. The head is set on a spindle as usual but instead of the crank -there is a large heavy disc on the bottom of the shaft and revolving in -a horizontal plane. This is within reach of the foot and the operator, -being seated, imparts a rapid motion by pushing, usually with the ball -of the right toe. The momentum is kept up by the weight of the disc and -there is a great advantage in that the foot need not be in continuous -motion. On the other hand it is difficult to acquire sufficient speed -and power for the work. - -There are several forms of machine wheels which are entirely -satisfactory but which need the application of power. If a gas engine or -a water motor or electric current be available, every effort should be -made to obtain a wheel of this description. The prime motion is imparted -to a short horizontal shaft which moves at a constant speed. Then the -operator, seated in comfort, regulates the speed of the wheel itself by -pressure upon a treadle. No action is required but a simple pressure, -light for a slow speed and heavy for rapidity. Where the electric -current is available, nothing could be better. Self-contained -motor-driven wheels are available but are rather expensive. - -One more plan may be mentioned in which the wheel is simply a vertical -lathe with a belt and handle to be turned by an assistant. This may be -convenient for some but it is not always possible to secure help at the -moment when the wheel is to be used. Moreover the cost of labor would -soon pay for a mechanical wheel.[G] - - [G] Information as to the usual types of wheel may be obtained from The - Crossley Manufacturing Company, Trenton, N. J.; The Patterson - Foundry and Machine Company, East Liverpool, Ohio; a wheel operated - like a sewing machine is sold by the Lewis Institute, Chicago. - -Whatever type of wheel is selected it should be arranged with a head -which can be removed. There are two methods of constructing this; the -head may be screwed on to the spindle, or the latter may terminate in a -cone-shaped plug upon which the wheel head is made to fit as in the -illustration (Fig. 14). The latter plan is to be preferred as the head -can be removed more quickly and is not so likely to work loose. Several -heads for the wheel can then be provided, one for regular work, one for -making plates, one for finishing and so forth. - -The regular operation performed upon the wheel is termed either throwing -or turning according to the industry in which it is employed, but in -this description the word "throwing" will be used because the subsequent -operation in which tools are employed is best described as turning. - -The best head for the wheel to be used in throwing is made of hard wood -or brass because the ball of clay can be easily centered upon a smooth -surface. This, however, involves that the work shall be cut off with a -wire and removed while soft. This is commonly done by professionals but -is beyond the skill of the beginner. It is best, therefore, to use a -head like that illustrated for plate making and to have a number of -specially shaped plaster bats to fit the recess (Fig. 17). Then when the -piece is formed, the bat with its burden can be set aside for the work -to harden. - -[Illustration: Fig. 17. Wheel head with detached bat.] - -Throwing is not an easy operation to describe but the following -instructions in the form of lessons will, with a large amount of -practice, enable the student to become fairly expert. Every opportunity -should be taken to watch a good potter at work. There are a thousand and -one little tricks in the position of the arms, hands, thumbs and fingers -which are impossible to describe but which can easily be copied. If a -kick wheel be used some time must be given to practicing the motion -without using clay. The action of the foot must become subconscious or -automatic like the pedaling of a bicycle so that simply to will a change -of speed is to accomplish it. - -[Illustration: Fig. 18. The progress of a clay ball on the wheel.] - -_Lesson I._ Take the bat about to be used, plunge it in clean water and -soak it nearly, but not quite, to saturation. If the bat remain wet one -minute after being taken from the water, it has soaked too long and must -be dried off a little. The effect of a wet bat is that the clay slips -and cannot be held in one place. The proper dampness is secured when the -clay ball can be pushed along the surface of the bat but does not slip -easily. This condition is important and should be secured by experiment, -because if not right, good work will be impossible. - -[Illustration: PLATE I. THROWING.--LESSON II, 1.] - -[Illustration: PLATE II. THROWING.--LESSON II, 2.] - -_Lesson II._ Place a small basin of water close at hand. Take a ball of -clay about three inches in diameter. Set it on the center of the wheel -as nearly as can be judged. Now spin the wheel at a fairly rapid rate. -Brace the left elbow against the side and, wetting the hand, press the -ball of the thumb and the lower part of the palm against the clay. The -left forearm being kept rigid, the clay as it revolves will be forced -into the center of the wheel. Use the right hand to sprinkle water on -the clay that proper lubrication may be maintained. With the fingers of -the right hand pull the clay towards you, at the same time pressing -inward with left hand and so squeezing the clay. As the hands come -together the clay will rise in a cone. Do not pull it upwards but let it -rise as it is squeezed. Now bring the hands over the top and with the -thumbs together press down again. Lumps and irregularities will be felt -in the clay and the operations of spinning up and pressing down must be -continued until these disappear. Repeat the exercise of centering with a -fresh ball of clay until it can be accomplished with ease and rapidity. -The clay so used is not wasted. The superfluous water may be dried off -upon a plaster bat and the clay wedged up for use again. - -[Illustration: PLATE III. THROWING.--LESSON II, 3.] - -This wedging or waging of clay--the word has descended from the old -English potters--is important. A strong table should be built of which -the top, measuring about 30 by 20 inches, is made of two-inch plank. A -raised edge two inches high is fastened firmly by being nailed to the -sides; the trough thus formed is then filled with plaster and allowed to -harden. An upright post is fastened in the center of one side and from -the top of this a fine brass wire is stretched to the other side of the -table, thus making a diagonal. The worker stands at the side of the -table opposite the post. The ball of clay is taken in both hands and cut -in two against the wire, then the pieces are slapped smartly upon the -plaster, one on top of the other. The whole lump is then lifted, cut in -two and slapped down as before. The lump of clay is thus formed into -layers, the irregularities in hardness are corrected and the clay made -smooth. A little practice will make the work quite easy but it will -often be found necessary to cut and beat the clay fifteen or twenty -times before a good texture is secured. If the plaster table be dry the -clay will be stiffened rapidly but the plaster may be made wet to -prevent this if it should not be necessary. A clay may also be softened -in this way by sprinkling it with water as the wedging goes on. - -[Illustration: PLATE IV. THROWING.--LESSON III, 1.] - -[Illustration: PLATE V. THROWING.--LESSON III, 2.] - -_Lesson III._ Center the ball as in Lesson II and moisten both hands and -the clay. Grasping the clay lightly but with sufficient force, press the -right thumb downwards and towards the palm and a cup-shaped hollow is -formed in the clay. Raise the right hand slowly, still keeping a light -pressure upon the clay with the thumb. The clay wall will rise with the -hand. Now insert the two first fingers of the left hand into the hollow -and hold them against the right-hand wall. Slacken the speed of the -wheel a little. Bend the forefinger of the right hand and press the -second joint and the knuckle against the outer wall so as to oppose the -fingers which are inside. Press the thumbs together to steady the hands -and raise both hands upwards together. The fingers inside and outside -the clay should be kept at a definite distance apart so that as the -hands rise, the clay is brought to a uniform thickness. The hands are -brought steadily to the full height to which the clay will go and thus a -cylinder is formed. - -Repeat this lesson three or four times with fresh clay. - -[Illustration: PLATE VI. THROWING.--LESSON IV, 1.] - -[Illustration: PLATE VII. THROWING.--LESSON IV, 2.] - -_Lesson IV._ Keep the hands wet. Shape the clay cylinder as directed in -the previous exercise. Now repeat the action of the fingers inside and -outside and, beginning at the bottom, take a closer grip of the clay and -draw up the walls as before. The cylinder is now taller and the walls -thinner. Do this again and again taking a little closer grip each time -until the cylinder is as tall and as thin as the clay will bear. The -walls will probably spread as the work proceeds and the hands must then -be used outside. Grasp the clay with both hands and squeeze it slightly; -at the same time raise the hands upwards. This will reduce the diameter -of the cylinder and thicken the walls. The operation of the fingers can -then be repeated until the full height is reached. There is, of course, -a limit to the height of the cylinder which can be made from a given -lump of clay and it is best to begin on a small scale. A ball of clay -which can be easily grasped with the hands is the proper size with which -to learn. A very small ball is nearly as hard to work as a large one. -Repeat this lesson until a tall cylinder can be made with ease and -certainty. - -[Illustration: PLATE VIII. THROWING.--LESSON V.] - -_Lesson V._ Keep the hands wet. Spin up a cylinder with thick walls as -in Lesson III. With the fingers of the one hand inside and those of the -other hand outside, open the cylinder gradually. Keep the wheel at a -slow speed. If the edge runs unevenly, use both hands outside to steady -it, then work outwards again until a shallow bowl is formed. - -[Illustration: PLATE IX. THROWING.--LESSON VI, 1.] - -_Lesson VI._ Keep the hands wet. Spin up a cylinder of medium height as -in Lesson IV. With the fingers of the right hand outside press inwards -at the base of the cylinder close to the bat and with the fingers of the -left hand inside, press outwards at a slightly higher level. This will -reduce the diameter at the bottom and increase it in the middle, making -a cup shape. Now raise the right hand and gently draw the top inwards. -With the left hand inside press the upper edge outward and with the -fingers of the right hand shape the upper part into the form of a jar or -flower pot. - -[Illustration: PLATE X. THROWING.--LESSON VI, 2.] - -[Illustration: PLATE XI. THROWING.--LESSON VII.] - -_Lesson VII._ Keep the hands wet; proceed as in Lesson VI. Instead of -making the top flange outwards, draw it gradually inwards into a globe -form. Work the clay carefully upwards and inwards until the opening at -the top is almost closed. Several attempts will probably have to be made -before this result can be secured. - -[Illustration: PLATE XII. THROWING.--LESSON VIII, 1.] - -_Lesson VIII._ Keep the hands wet. Spin up a globe shape with a narrow -base as in Lesson VI but carry a good share of the clay to the top so -that the upper edge of the globe is quite thick. Insert two fingers of -the left hand and with the fingers of the right hand outside work the -upper edge of the globe into a tall neck. The action is the same as in -the shaping of a cylinder except that the diameter is smaller. A good -deal of practice will be necessary in order to keep the neck thin and to -raise it to any appreciable height, but perseverance will accomplish it. - -[Illustration: PLATE XIII. THROWING.--LESSON VIII, 2.] - -These lessons if carried out conscientiously will enable the operator to -produce almost any form in so far as the manipulation of the clay is -concerned but the work up to this point is drill only. It is not -intended that the pieces should be preserved. The next point is to -insist that the clay obey the potter in the shaping of a form. - -A simple drawing of a jar should be made exact to the size proposed. Two -or three pairs of calipers are provided and with them the diameter of -each part of the drawing is taken. Of course a single pair could be made -to serve, but it is very inconvenient to change measurements while -working. A piece of wood also is cut to the height of the proposed -piece. The throwing is begun as usual by making a cylinder. This should -be higher than the drawing for the clay sinks in the shaping. First the -bottom is pressed into the proper size (Lesson VI). Then the body is -enlarged to the required measure and, lastly the diameter of the top is -taken and the height brought to the determined point. If too high the -superfluous clay may be cut off with a pointed knife, the edge being -carefully rounded afterwards. - -It is only by checking up one's work in some such way as this that real -power can be acquired. The skilled worker can think in the clay and -create forms at will upon the moving wheel, but for the beginner to -attempt this is like an endeavor to paint pictures before one has -learned to draw. Shape after shape should be designed, drawn to scale -and thrown to measure; in fact, for elaborate pieces no other course is -possible. - - - - -CHAPTER X: TURNING - - -It is not possible to finish work to perfection in the operation of -throwing. The clay is too soft to handle and for proper finishing the -piece must be turned over to get at the bottom. An experienced thrower -reduces the final work to a minimum and this, of course, is the ideal -plan but even in factory practice every thrown piece is passed on to the -turner so that the phrase "thrown and turned" is used as of a single -operation, though it, in fact, expresses not only two processes but the -work of two men. - -The artist-potter must needs, therefore, learn to turn, though this -process should not be worked to death as it is liable to be. Many -persons in the pride of having produced some sort of a form on the wheel -will leave it in the crudest possible condition and trust to the turning -tool to remove defects. If the lessons on throwing have been -conscientiously carried out, this error will not be committed. - -A half dozen cylinders of convenient size should be thrown on separate -bats and set aside in a cool place to harden. They must not be dried but -should be in the condition known as "leather hard." If thrown one day -they will be ready for turning the next morning. Pieces thus hardened -are no longer flexible. They can be handled freely and the clay can be -easily cut with a knife. - -[Illustration: Fig. 19. Turning tools bent and sharpened.] - -The equipment for turning consists of a board support, a turning stick -and a set of tools. The board is of soft pine, eight or ten inches wide -and two feet high and is set upright at the back of the wheel frame -opposite the workman. It may be screwed in position if it does not -interfere with the throwing, or it may be set in a socket so as to be -removed when not in use. Its purpose is to support the end of the -turning stick. The stick is an ordinary broomstick in the end of which -is a sharpened nail. In use the end of the stick is held in the left -hand and the point is pressed into the board at any required height. The -right hand, holding the tool, is rested on the stick just as the hand of -a painter rests on the mahl-stick. - -The turning tools are of soft steel.[H] They are purchased unshaped and -the potter must learn to bend and file them to suit himself. A section -of bench should be set apart for filing and care must be taken that the -steel dust does not get into the clay. - - [H] The Milligan Hardware Company, East Liverpool, O. - -One of the cylinders, with the bat upon which it was thrown, is now -taken in hand. Many beginners try to turn their pieces without detaching -them from the bat, trusting to the original adhesion to hold the piece -in position. This is a very unsatisfactory plan. A fundamental principle -in craft work is that the mechanical difficulties in manipulation should -be met and overcome at the first. If one trusts to some method which is -apparently easy one walks with crutches and there will come a time, if -progress is to be made, when such helps must of necessity be abandoned -and then the learning must be begun again. Therefore the student is -advised to face the mechanical technique at the very beginning. The -cylinder may be turned on the throwing bat, but there is a better way. - -The piece should not become so hard that it will release its hold on the -bat but with a long bladed knife it should be cut away. If the knife be -held close to the bat a separation is easily effected. Set the -leather-hard cylinder upon a new bat which is slightly damp and which -runs true, on the wheel. The first problem is to center the work. A -pencil line may be run upon the bat making a circle just the size of the -cylinder. Then as the wheel is revolved it will be seen if the piece -runs true. It is quite unlikely that this will be the case. Perhaps the -bottom is true but the top circle is untrue. In other words, the axis of -the cylinder is not upright. Turn the cylinder upside down and try if it -will run any better. If it does the work may be begun in this position. -If it does not, turn it back again. Now take a pencil and hold it with a -steady hand so that it just touches the near side as the wheel goes -round. Lift up the edge of the cylinder on the side marked by the pencil -and slip a morsel of clay under it. Revolve the wheel and try with the -pencil again. In this way raise or press down one side, keeping the -bottom circle in the center until both top and bottom are running as -nearly true as they can be made. This, so far, refers only to the -horizontal planes. If one side is higher than the other it does not -matter at present. Now take three small pieces of soft clay, and, -holding the cylinder firmly with one hand, press them down at -equidistant points in the angle where the piece joins the bat. This -serves to hold the work in position. A square turning tool of small size -is the best to begin with. It is held in the fingers as a pen is held -but more firmly. The right hand rests on the turning stick and, the -connection between hand and stick being as rigid as possible, both are -moved together. This is better at first than moving the right hand -freely for to do so will surely result in irregular work. - -The tool should be held so as to cut with one corner at first and it is -well to take one cut, remove the tool, take another cut and so on. The -object should be to feel the clay and to test its resistance. No one can -be a successful potter who does not cultivate a sympathy for the clay. -The tool is to cut, not to scrape. That is, the cutting edge is to be -opposed to the revolving clay. The point at which the tool touches the -clay is opposite the center or at the same distance from the operator as -the center of the wheel is. If nearer to the workman the tool will not -cut; if further away, it will scrape and pull (Fig. 5, page 50). - -The first efforts should be directed towards acquiring skill. The -student should endeavor to make a cut at any desired point without -regarding the effect upon the shape of the cylinder. In other words the -clay is used merely as a practice piece. It is not to be preserved. It -is a good plan to keep on turning the first piece until it is all turned -away. Too many students fail because they wish to have a piece to keep. -He will make the best ultimate success who cares nothing for the -preservation of a dozen or two cylinders or other shapes, but uses them -merely as exercises in manipulation. If the student is over anxious to -avoid spoiling his work, he grows nervous and so loses control of his -tools and material. To set no value on the practice pieces themselves -begets confidence and this is the surest aid to success. - -After two or three cylinders have been centered to the pencil line the -attempt to center one free-hand may be made. Place a cylinder on the -wheel but not quite in the center. Spin the wheel at a medium rate. Fix -the attention upon the eccentric motion, trying to forget the circular -motion. As the cylinder appears to move from side to side tap it lightly -with the hand so as to drive it towards the center. In all probability -this will result in driving the cylinder off the wheel altogether. Some -little practice is needed, but if persevered in the result will be a -power of convenient and rapid centering which is never forgotten and -which is the greatest possible help to successful work. One may practice -with a wooden cylinder or even a tin can if the weight approximates that -of the clay pieces. - -[Illustration: Fig. 20. Turned feet. _A B C_, feet for small pieces. _D -E F_, feet for large pieces. _G H I_, common faults in foot finish.] - -Accompanying the practice in turning there should be some exercise in -the shaping and filing of tools. Broad tools filed to the proper curve -are indispensable in finishing concave surfaces. A curved edge may also -be put upon one or two narrow tools. These will cut more rapidly than -the broader ones but will not leave as smooth a finish. Whatever tool be -used the final surface must be worked over with a soft sponge and water -so as to eliminate the tool marks and leave a plastic surface. One of -the principal troubles with which the beginner will meet is the -vibration of the tool known as "chattering." This is sometimes so slight -as not to be felt by the hand but when the motion of the wheel is -stopped the work will be found covered with fine ridges like gathering -on muslin. The way to prevent this is to avoid using the broad edge of -the tool until some experience has been gained. The way to cure it is to -go over the work again with a fine pointed tool and then to use the -sponge liberally. The point of the tool cuts through the small ribs or -wrinkles whereas a broad tool would ride over them and make the trouble -worse. - -While the whole surface of the work will probably need more or less -turning, the chief part of the operation is concerned with the under -part or foot. The formation of a good foot marks a good potter and vice -versa. Before beginning to turn it should be decided what kind of a foot -is desired. Each shape has its own style. Some sketches are given here -with an idea of the form to which each is adapted. They are shown upside -down because the work is done in this position. The small bevel at the -outer angle is used for facility in glazing. A foot finished thus always -has a neat appearance when the glaze has been removed from the beveled -face. - - - - -CHAPTER XI: MAKING LARGE PIECES - - -There is a limit in size beyond which the non-professional will not be -able to go. Men of life-long experience can throw very large jars but -this involves not only more practice than the artist-potter can hope to -secure but also great physical strength. On the other hand it is -perfectly possible to form vases two or three feet in height by doing -the work in parts or sections. No one need fear to put such a plan in -operation on account of sentiment. It is, of course, worth while to make -large wares in a single piece but section work involves great skill and, -as a rule, the result attained is better. Work made in one piece is apt -to be badly finished, especially inside, and unduly heavy. Work made in -sections can be thrown with thin walls and finished with proper care. If -tradition be of any help, be it known that the Chinese have used the -piece method for hundreds of years, and that the Greeks used it three -thousand years ago. - -The first requisite is a drawing either actual size or properly scaled. -The measurements should be those of the soft clay and if a particular -size be desired in the burned piece, the shrinkage, probably about -one-eighth, must be added. The drawing must show the size of each -section with the points of junction, and should indicate the upper and -lower edges in each case. Some divisions are best made right side up; -some are more easily thrown upside down. Care should be taken that the -faces which are to be joined are thrown under similar conditions. In -every piece of work one face rests on the bat, the other is in the air -or free. A bat face should always be joined to a bat face and a free -face to a free. - -Suppose, for instance, a vase is to be sixteen inches high and is to be -thrown in four divisions of four inches each. The bottom division is -made first. This will stand in its normal position, right side up. The -second section must now be thrown upside down, because, if it were not, -its bat face would be joined to the free face of the first piece. So the -sections are thrown alternately, every other one being inverted. - -[Illustration: PLATE XIV. MAKING LARGE PIECES. THE FIRST SECTION.] - -As the pieces are thrown they must be carefully measured to see that the -faces which are to be united are the same size. The height of each piece -also must be gauged and adjusted. The bats with their contents are now -set aside to harden. As soon as they can be handled with safety the clay -pieces should be removed from the bats upon which the throwing was done -and set upon dry bats which will absorb the moisture and help to stiffen -the clay. It is a good plan to pile the sections up as they are to stand -in the finished piece, one upon another and to leave them so in a cool -place for ten or twelve hours. The faces which are to be joined will -thus acquire a uniform hardness and unequal shrinkage will be avoided. - -When all is ready for the turning, the sections being of the proper -hardness are taken in hand. This work should not be hurried. It will -take a whole morning to put together a large piece. First, the bottom -section is placed on the wheel, centered and made to run true as regards -the top edge. It is then inverted and the foot is properly finished, -signed and dated. Then the second joint is likewise turned true on both -faces, the inside turned smooth; and so on, each piece in turn is -prepared for the fitting, the measurement of each face being accurately -adjusted. At this stage it is possible to correct the diameter of the -faces to some extent either by pressure as the wheel revolves or by -building up with soft clay. In either case, however, the new work must -be hardened before proceeding. The whole piece is now put together -carefully but with dry joints. It should be slowly revolved on the wheel -and the proportions carefully criticised. If satisfactory it is taken -apart again and the actual fitting up may proceed. - -The bottom section is again centered most carefully on the wheel and -steadied with three pieces of clay. A thick slip is now prepared, the -same clay as that used for the work being of course, used. This slip -must be quite free from lumps and should be as thick as molasses. The -upper edge of the work is carefully sponged with clean water and a good -coating of slip is applied at the junction. Care must be taken that -every part of the face is covered with slip. The second joint is now -moistened at the junction and set in position upon the bed of slip. It -is placed very lightly and the wheel is gently revolved to see if the -running is true. If so it is pressed home and the superfluous slip is -removed. The joint should be quite close like a glued joint in -carpentry. - -In the same way the third section is placed upon the second and the -fourth upon the third. It is now possible to work over the face of the -vase with a little soft clay. There is almost always some irregularity -in the line, especially at the joints, and this must be adjusted while -the work is moist. Then the whole face is gone over with turning tools -and sponge and the vase is set aside to dry. It must not be expected -that large pieces, made by any method, will be produced with as much -ease as small vases and bowls. The risks are much greater and, owing to -the size of the work, the faults are much more apparent. When the vase -is perfectly dry it should be set on the wheel, centered and slowly -revolved. If it is very untrue in its motion there is no remedy. It -should be broken down and the clay used again. A very slight -irregularity may be corrected by rubbing off a little clay on one side -of the foot but this cannot be done to any considerable extent. The -courage to break unsatisfactory work is never more valuable than at this -juncture. It will pay in the end, for no imperfect piece can be a source -of satisfaction to the conscientious craftsman. - -[Illustration: PLATE XV. MAKING LARGE PIECES. Measuring the Foundation -of the Second Section.] - -[Illustration: PLATE XVI. MAKING LARGE PIECES. Drawing up the Second -Section.] - -[Illustration: PLATE XVII. MAKING LARGE PIECES. Shaping the Third -Section.] - -[Illustration: PLATE XVIII. MAKING LARGE PIECES. The Three Sections -Completed.] - -[Illustration: PLATE XIX. MAKING LARGE PIECES. Turning the Edge of the -First Section. (Note the other sections on the table.)] - -[Illustration: PLATE XX. MAKING LARGE PIECES. Finishing the Bottom of -the First Section. (Note the second section in the foreground ready for -turning.)] - -[Illustration: PLATE XXI. MAKING LARGE PIECES. Checking the Size of the -Second Section.] - -[Illustration: PLATE XXII. MAKING LARGE PIECES. Fitting Together Dry.] - -[Illustration: PLATE XXIII. MAKING LARGE PIECES. Setting the Third -Section in Place.] - -[Illustration: PLATE XXIV. MAKING LARGE PIECES. The Three Sections Set -Together in the Rough.] - -[Illustration: PLATE XXV. MAKING LARGE PIECES. The Finished Vase.] - - - - -CHAPTER XII: CUPS AND SAUCERS AND PLATES - - -It is not likely that many craftsmen will care to produce table wares or -even that they will be able to acquire the necessary skill. Simple as -these wares seem, they are, in fact, the most difficult of all to make -well. In factory working, one man makes nothing but cups, another -saucers and another plates, so that each attains the skill of constant -practice, but this is out of the question for the studio worker. At the -same time it is well to know how it is done and it may be that some one -will undertake to produce a few pieces for the sake of the enjoyment -arising therefrom. - -It is possible to finish a cup upon the wheel just as a vase is made. -The handle is modeled in clay and fastened in place with slip when in -the leather hard condition. Saucers and plates cannot be made in this -manner; first, because the broad thin bottom will surely crack and, -second, because it is impracticable to turn a plate or saucer over in -order to finish the bottom. The risk of breakage is so great that there -is nothing to be gained. - -If cups be needed of uniform size they must be molded. The making of the -molds has already been described. A small cylinder of the proper size is -thrown in clay and removed from the wheel while soft. A number of these -should be made at one time so as to avoid changing the wheel head often. -When all are ready a hollow head shaped to receive the cup mold is set -on the wheel and a mold inserted. One of the soft cylinders is now -lowered gently into the mold and as the wheel is revolved the soft clay -is pressed firmly against the walls with the fingers. A piece of wood, -called a rib, cut to the exact shape of the inside of the cup, is used -to smooth off the interior. The top edge is cut off and rounded and the -mold is set aside for the cup to harden. As soon as the cup can be -turned out it is set upside down upon the wheel and the bottom turned. - -Another method dispenses with the formation of the cylinder or "lining." -A ball of clay of the proper size is dropped into the mold and pressed -into shape with the fingers, the wheel, of course, being spun. The -finishing is accomplished with the rib as before. This method will -answer for wares which are to receive a low fire but for high -temperatures the clay must be handled by the first-named plan. - -The cup is not complete without a handle. This may be modeled as already -stated but to make each one of half a dozen in this way is unduly -tedious. The better plan is to model a handle in wax and make a mold as -already directed. A roll of soft clay is then laid in the mold, the two -halves pressed together and the handle taken out and finished. Care must -be taken that cup and handle are of the same degree of moisture, leather -hard, for choice, or they will part company as they dry. The fastening -is done with thick slip. - -The method for saucers is the same as that for plates, so that one -description will suffice. The first step is to make a tool or profile. A -large handful of soft clay is rolled out into a thick cylinder and laid -down upon the plate mold. It should extend from the center to the -circumference, forming a radius of the circle. The clay is pressed -closely to the surface of the mold and part of it is squeezed into a -knob which will form the hand-hold of the tool (Fig. 16, page 66). The -clay is left in this position until it becomes nearly but not quite dry. -It is then taken off and whittled into shape. The front edge must be -straight and must lie along a radius of the plate. The foot is cut in at -the proper point and a broad wedge-shaped hollow is made so as to gather -the clay and pile it up into the foot. The hand-hold is shaped so as to -fit comfortably between the first and second fingers of the right hand. -When properly shaped the tool is thoroughly dried and then burned in the -kiln. The fire must not be severe as it is important not to shrink the -tool to any great extent. After burning slight corrections can be made -with a file or a hard stone. The heel of the profile must be exactly at -the center of the plate and the toe or curve must rest on the outer edge -of the plate mold. - -In making plates a "batting block" and "batter" are used. The former is -a heavy block of plaster which is fixed to a strong table. It must be -saturated with water when in use. The wedging table already described -will serve for this. The batter is a disc of plaster to which a handle -is attached. It may be made of a thick plaster block, the handle being -cut out of the substance itself. This is also kept saturated with water -so that the clay will not stick. A ball of clay is laid on the block and -gently beaten out with the batter into a disc of the proper size and -thickness. The face of this is then polished with a steel blade and the -disc is then lifted, turned over and laid, polished side downward, upon -the mold. The wheel is then revolved and the clay pressed firmly to the -mold with wet hands. The tool is now dipped in water and pressed -steadily upon the revolving clay. The heel must be adjusted accurately -to the center and the foot will be seen to rise up in its proper place. -The operation is not easy and many failures must be expected but -practice will accomplish the desired result. When leather hard the plate -is gone over with a thin piece of rubber and when quite hard it may be -removed from the mold. The edge is now trimmed and the face sponged over -and the plate is ready for the kiln. - - - - -CHAPTER XIII: CASTING - - -In commercial production the casting method is constantly used. It is a -means of making light and delicate pieces with ease and, of course, all -the pieces cast in the same mold are alike. This very fact, however, has -led to the method being disregarded by the studio worker who does not -wish to duplicate anything that he makes. If a single piece only is to -be made the work involved in molding is a waste of time and it is better -to strive for skill at the wheel, and yet there are occasions when a -knowledge of casting is of great value. In the preparation of trial -pieces there is no method better. To make these in sufficient number on -the wheel would be tedious except for the benefit of the practice -involved. - -Directions for making molds have already been given and the slip which -will have been prepared in the process of clay making is ready for the -casting process. This slip should be thick, about the thickness of -buckwheat batter. To be accurate, a pint should weigh 26 ounces. For -small pieces or for vases with narrow necks it is advisable to use the -slip rather thinner. For large wares, on the other hand, or for open -bowls it may be slightly thicker. A few experiments will show the reason -for this. Two quart jugs are needed. They should be large of neck and -should deliver their contents freely and completely. Jugs with a deep -shoulder are not good as the slip hangs in the pouring. One of these -jugs is filled with slip which is to be poured carefully from one to the -other, allowing it to flow gently down the side. This is to break the -air bubbles which are nearly always found to be present and the pouring -should be repeated until the slip flows smooth and even. - -The mold, being thoroughly dry, is tied around with twine, if in parts, -and wedged firmly so that it cannot leak. The slip is then carefully -poured so as not to touch the sides and the mold is filled until a small -mound of slip rises over the edge. This mound will at once begin to sink -as the water is drawn into the walls of the mold and slip must be added, -little by little, to make good the loss. A small quantity of clay will -now be found to have stiffened at the rim of the mold and if this be -carefully removed with a steel tool the thickness of the wall of the -vase will be seen. If not thick enough the mold must be continually -filled up until the necessary thickness is attained. The mold is then -carefully lifted, making sure that the bottom is held firmly, and the -slip is poured out. It should not be poured back into the casting-jug -but into another vessel. - -The mold is now set upside down to drain. It should not be placed upon -the table but upon two sticks laid parallel so that the drip may hang -clear. Several molds may be filled in this way at one time and after -about twenty minutes the one first filled may be opened. The bottom is -gently detached and the upper part of the mold, consisting of two -halves, is laid upon the table on its side. A little gentle manipulation -will now suffice to lift the one half and the vase will be seen lying in -the other half as in a cradle. The clay is still very soft and must be -treated carefully. The half mold, with the contained vase, is taken in -the left hand and held nearly upright, the fingers below, the thumb on -the top. Now set the fingers of the right hand under the bottom of the -vase, rest the thumb lightly against the side and tilt the half mold -gently forward. If mold and clay are in good condition the vase will -fall forward to be supported on the fingers of the right hand and -steadied by the thumb. The half mold is now laid down and the vase taken -in both hands, set gently on a plaster bat and put aside to dry. It -often happens that the vase leaves the mold with reluctance. If the slip -be very new, or the mold either damp or hard or worn out there will be -some difficulty in effecting a separation. By allowing the work to stand -a while, however, and by slightly jarring the mold from time to time -with the ball of the thumb the piece can generally be removed without -damage. - -In using a new mold it is customary to make what is called a "waste -filling." The mold is filled with slip and at once emptied. After -standing a few minutes it is forcibly opened and the thin layer of clay -inside is picked out with a ball of plastic clay pressed against it. A -tool should never be used as this will damage the face of the mold. If -the clay should stick obstinately a soft cloth used over the finger will -remove it. The reason for this waste filling is that it removes the scum -which occurs on all new molds. - -Cast ware should not be touched until quite dry and then the spare at -the neck is carefully cut off, the seams scraped down and the whole -surface smoothed with fine sand paper and a soft cloth. Worn out linen -serves excellently for this purpose. - -Cups and bowls, if molded, are made without spare at the top. In this -case great care must be taken to see that the edge is left clean and -smooth in the casting. The spare neck on a vase acts as a margin of -safety, as it is completely cut away in the finishing. If a piece has no -spare the edge must be left without blemish at the first. - - - - -CHAPTER XIV: TILES - - -There are two methods of making tiles, the dust-pressed method and the -plastic. The former is the more usual commercial plan but the appliances -for preparing the dust and the heavy presses necessary are not adapted -to studio work. The dust-pressed tile is, moreover, somewhat mechanical -in surface. It is not suitable for modeling or for any treatment but -those of glaze and color. The plastic tile, on the other hand, may be -treated by plastic methods and the surface offers a texture which -appeals strongly to the artist. - -For the successful production of tile a special body is necessary. -Ordinary pottery clay is too close in grain and straight tile cannot be -made from it. Small square pieces, however, such as tesseræ, can be made -from any clay. - -It is presumed that a pure white tile body is not required. For studio -work the most pleasing white surface is found in an opaque enamel, but -for the most part the craftsman will wish to work for colored tile. A -cream or buff body is all that is necessary, therefore, and the -foundation of this is a clay known as sagger clay. In order to secure -the necessary porosity a fine "grog" must be used. Grog is burned clay. -After working awhile there will be an abundance of this in broken -unglazed pottery but at first some soft fire-bricks must be pounded. -This is laborious work, but a boy can usually be hired to do it. The -brick or broken pottery is crushed in an iron mortar but should not be -broken too fine. Two sieves are necessary, one of 20 and one of 40 -meshes to the linear inch. The coarse powder which passes through the 20 -mesh and lies upon the 40 mesh is used. This is called 20-40 grog. The -dust which passes through the 40 mesh may be saved for kiln work. It is -useful for setting biscuit pieces one upon another as it will -effectually prevent sticking. This powdered grog is also useful in the -case of flowing glazes. A thick layer on the bottom of the kiln will -catch any drops of glaze and save the kiln from damage. - -A quantity of the 20-40 grog having been prepared, a mixture should be -made of:-- - - Sagger Clay 550 parts - 20-40 Grog 300 parts - Ground Flint 150 parts - -The clay should be finely pulverized and the whole mixed in the dry -state. Water is then added, little by little, until a rather soft mass -is obtained. It is not practicable to mix clay of this description by -the slip method because the grog would settle out and fall to the bottom -of the vessel. It sometimes happens, however, that the stoneware clay -contains grains of iron which cause black spots to appear in the tile. -If these cause trouble the clay must be made into slip first and lawned -through 120 mesh. It is then allowed to become very thick and the grog -is stirred in. This is a good deal more trouble than the first named -plan and is not often necessary. - -Tile are sometimes made in plaster molds. A tile of the proper size is -cut from a plaster block and a mold is made from it. If a modeled -surface be desired clay may be modeled upon the face of the plaster tile -before the mold is made. The mold will then receive the embossment in -reverse and all the tiles made from this mold will be alike. The clay is -pressed into the mold while quite soft and is scraped off level at the -back. Thus it is the face of the tile that is shaped by the plaster. If -this plan be adopted the tile must be removed from the mold as soon as -possible. If left to dry in the mold they will warp because of the -unequal absorption. - -A better method has been devised by the author and has been put into -practice with considerable success. When the size of the proposed tile -has been determined a board is made which is large enough to hold a -square of the tile, say twelve or sixteen. Thus if a tile five inches -square is to be made the board would be fifteen by twenty inches for -twelve tile or twenty inches square for sixteen. On each side of the -board a wooden rim is fastened and this must stand higher than the board -to the exact thickness of the tile. About five-eighths of an inch is -enough. The board must be perfectly rectangular and marked off at even -distance of five inches and a shallow groove is cut at each point. - -To make the tile the board is wetted and an even coating of grog dust is -sprinkled upon it. A ball of clay is laid in the center of the board and -rolled out with a rolling pin to fill every part of the frame. With a -straight edge the clay is struck off smooth and clean, working always -from the center outwards. Reversing the plaster mold method the tile are -now face upward and any kind of surface may be given at will. The clay -may be lubricated with water and made smooth or it may be sprinkled with -grog dust which will give a sandy or toothed finish. The square is now -to be cut into tile and this is done with a slender knife and ruler. The -ruler should not rest upon the clay but upon thin strips of wood or -cardboard which may be laid along the edges for the purpose. The cutting -should not go quite through the clay as, if a slight connection be -allowed to remain at the bottom, the tile will keep each other straight. -When the cutting is finished the board should be set at an angle of -forty-five degrees for the clay to harden. When leather-hard the whole -may be turned gently over and the tile allowed to fall on to a board -placed in readiness. They are now broken apart, trimmed if necessary and -set aside to dry. - -Tile made in this way can be kept straight without difficulty and the -method is much more expeditious than pressing in plaster molds. - -If a modeled surface be intended it is quite easy to work on the tile in -the tray while the clay is soft. Forms may be cut in wood and pressed -into the clay in any variety and the charm of individual treatment is -preserved. - -The body given above will prove quite porous when fired but it will take -matt glazes well. A little crazing is no detriment to tile because they -are not like vessels which are meant to hold water. If a denser body be -wished for some of the flint may be replaced by spar. - -One of the most attractive methods of decorating tile is by means of a -white or delicately tinted enamel and color. The opaque tin enamel given -on page 134 will answer well and if the whiteness prove too intense it -may be modified by a very small addition of under-glaze color according -to the tint desired. The tile should be glazed rather thick. Not as -thick as a matt glaze but thicker than bright glazes. The glaze or -enamel should be poured into a flat tray which is large enough to -receive one tile. The tile is taken by the edges between fingers and -thumb and held face downwards. Do not let either fingers or thumb -project beyond the face. The glaze having been well stirred the face of -the tile is allowed to rest upon it for about two seconds. The hand is -then lifted quickly and reversed so that the tile is face upwards. Every -effort should be made to avoid streaks or tears and a little practice -will accomplish this. If the glaze shows a bad surface it should be -scraped off. It can be mixed up and used again. Sometimes a slight -wetting of the tile before glazing will help the surface to flow evenly. - -The decoration is carried out with ordinary under-glaze colors. These -may be mixed together to produce any hue which is sought and a little of -the glaze itself, about ten per cent., should be mixed with the color. -This will assist in uniting the color with the glaze so that they melt -together. - -To produce enamel decorations at their true value the color should be -painted upon the dry glaze before it is burned. The best relation -between surface and color is thus secured. The color must be worked -quite thin with water and a little glycerine. A quick, sure stroke is -needed as no change or erasure is possible. The design may be made on -paper and traced or pounced on to the glaze with lamp-black. - -For burning the tile there is nothing better than little fire-clay -boxes. These can be made in a mold without difficulty and the inside of -each should be washed with glaze. If some such protection be not -provided dirt is almost sure to fall on the flat surface and the tile -will be spoiled. It is not possible to rear them on edge in the kiln for -burning as then the glaze would flow to the lower side and cause an -unsightly ridge. - - - - -CHAPTER XV: GLAZES AND GLAZING - - -PART I - -Much of the fascination of pottery making centers in the glaze. At one -time a great deal of mystery appeared to surround the composition and -use of glazes, but if one will take the trouble to learn, much of this -may be dispelled. Some knowledge of chemistry is desirable if an -understanding of the theory of glaze-making is to be acquired, but a -good deal may be learned even without this knowledge. Only such simple -instruction as can be assimilated by ordinary intelligence will be -attempted here, as an exhaustive treatment of the subject would be long -and tedious. - -It is possible to purchase glazes ready for use[J] but the true -craftsman will not be satisfied until he can prepare his own. - - [J] The Roessler & Hasslacher Chemical Company, 709 6th Avenue, New - York City, manufacture glazes according to the recipes of the - author, and also chemicals for use in the laboratory. - -Glazes[K] belong to a class of chemical compounds known as silicates; -that is, they have silica as the characteristic ingredient. Clear glazes -are compound silicates of lead, zinc, lime, potassium, sodium, aluminum -and boron. Matt glazes are characterized by certain of these ingredients -being present in excess; and stanniferous or tin glazes are, as the name -implies, rendered opaque by the use of oxide of tin. - - [K] It is admitted that glazes are not chemical combinations but solid - solutions, but the principle is more easily understood when the - analogy of chemical action is adopted. - -The commonest type of glaze is that which is made from ready prepared, -commercial substances. These are called raw glazes as being made from -raw materials or materials which need no preparation. - -It is possible to mix a glaze in a druggist's mortar by hand, using fine -sieves, but if the best results are to be secured, a small mill must be -used for grinding. The best form of mill is the ball mill or jar mill. -This consists of a porcelain jar which is set in a frame and made to -revolve upon its axis in a horizontal position. It is about half filled -with porcelain balls and these as they roll against each other perform -the grinding. These mills may be purchased ready for use, either as a -single jar to be worked by hand or a battery of two or more revolved by -power.[L] - - [L] Paul O. Abbé, 30 Broad Street, New York City. - -A good pair of scales is a necessity and it will be found convenient to -use metric weights which need no calculation into pounds and ounces. -Suspended scales are not as easy to use as the form known as counter -scales or balances. They should have movable pans which are usually -nickel plated. Upon these the materials can be placed direct without the -use of pieces of paper, which are always troublesome and inaccurate. -There should be a graduated bar on the front for the adjustment of -weights of five grams and under. This avoids the use of small weights -which are always being mislaid and lost. Dealers in chemical supplies -keep these scales in stock and the cost is about eight dollars. A set of -weights must also be procured from one hundred grams to five grams -inclusive. These need not be of the accurate adjustment which are used -in analysis. A good inexpensive grade is sufficient. - -The ingredients for glazes are given in the following list: - - Commercial Chemical Symbol or Equivalent - Name Name Formula Weight - - White Lead Lead Carbonate Pb(OH)_{2}2PbCO_{3} 258 - - Zinc Oxide Zinc Oxide ZnO 81 - - Soda Ash Sodium Carbonate Na_{2}CO_{3} 106 - - Niter Potassium Nitrate KNO_{3} 202 - - Whiting Calcium Carbonate CaCO_{3} 100 - (Carbonate of Lime) - - Feldspar Orthoclase K_{2}O,Al_{2}O_{3},6SiO_{2} 557 - - Kaolin Aluminum Silicate Al_{2}O_{3},2SiO_{2},2H_{2}O 258 - or China Clay - - Flint Silica SiO_{2} 60 - - Borax Sodium di Borate Na_{2}B_{4}O_{7}10H_{2}O 382 - - Boric Acid Boric Acid B_{2}O_{3}3H_{2}O 124 - -For coloring, the following metallic oxides are used: - - Color Chemical Symbol or Equivalent - Name Formula Weight - - Blue Cobalt Oxide CoO 80 - - Blue and Green Copper Oxide CuO 79 - - Gray and Brown Nickel Oxide NiO 75 - - Brown and Yellow Iron Oxide Fe_{2}O_{3} 160 - - Brown Manganese Carbonate MnCO_{3} 115 - -Under-glaze colors may also be used for coloring glazes, the color being -ground with the glaze batch. - -It is not absolutely necessary to commit the formula and equivalent -weight to memory. They will soon be remembered as use becomes second -nature. - -A glaze is usually expressed as the chemical formula. In this there are -three divisions given, each of which expresses a distinct function. On -the left hand are the bases, the foundation of the glaze. These indicate -the type, such as lead glaze, a lime glaze, an alkaline glaze, etc. All -glazes being silicates, this is the usual way of distinguishing them. In -the center are the alumina and boron oxide. These regulate the behavior -of the glaze in the fire. They make it viscous or sluggish as it melts -and prevent a too rapid flow. The alumina is infusible, the boron is -fusible, but boron cannot be used in a raw glaze for reasons to be -presently explained. At the right stands the silica, the dominating -factor with which all the other ingredients combine, and which controls -the behavior of the whole as regards the fitting of the glaze to the -body. - -The very simplest form of glaze is a bisilicate of lead, represented by -the formula PbO, SiO_{2}, or one equivalent of lead oxide and one of -silica. The term "equivalent" means that the mixture is calculated, not -upon the actual weight of a substance but upon its equivalent or unit -weight. Thus the equivalent weight of lead oxide, PbO, being 222, in -order to produce the formula in actual weight 222 grams or pounds must -be weighed out. It does not matter what weights are used so long as they -are the same for all. - -In like manner the equivalent weight of silica is 60 and as flint is -pure silica, the formula PbO, SiO_{2} would be produced by weighing-- - - Litharge or Lead Oxide 222 parts - Flint or Silica 60 parts - -Litharge is not, however, a convenient substance to use. It is very -heavy and does not mix well in water. The most usual substance for the -introduction of lead oxide is white lead. This is not lead oxide but it -changes to lead oxide when burned. White lead bears the formula -Pb(OH)_{2}, 2PbCO_{3}, which, being dissected is found to be 3PbO, -H_{2}O, 2CO_{2}. H_{2}O is water and CO_{2} carbonic acid, both of which -pass off in burning. Both, however, are weighed when the white lead is -put on the scales and therefore the equivalent weight of white lead is -258 and not 222. - -The mixture for practical purposes then would be-- - - White Lead 258 parts - Flint 60 parts - -Which, when ground and spread upon the ware would be a very fusible -glaze of a yellowish tone. - -This was spoken of as a bisilicate of lead because the measure of the -silica, also called the acidity of a glaze, is calculated upon the -oxygen contained in the base and the silica respectively. PbO contains -one molecule of oxygen, SiO_{2} contains two. Hence the relationship of -the oxygen in the base to the oxygen in the silica is as one to two. -This is called simply the "oxygen ratio" and is of great importance in -determining the behavior of a glaze. While this simple bisilicate of -lead will be a glaze under certain conditions it is found to possess two -faults. 1. It is too fluid under fire. The glaze will run down a -vertical surface and leave the upper edge of the piece bare. 2. If -subjected to a long slow fire it will lose its gloss and become -devitrified. This devitrification is often seen in commercial work and -appears as a dull scum in patches and around the edges of the ware. It -is, in fact, a crystallization of the silica which separates out, as -salt does from an evaporated brine. Both these faults may be corrected -by the addition of a little alumina to the glaze. A whole equivalent of -alumina would be too much, in fact it is found in practice that .2 -equivalent is sufficient for most lowfire glazes. In order to maintain -the oxygen ratio and to keep the glaze as a bisilicate the silica -content must be raised. Alumina contains three molecules of oxygen so -that the total amount of alumina is multiplied by three and the silica -brought to the equal point thus: - - PbO, .2Al_{2}O_{3}, 1.6SiO_{2} - -The amount of silica required in any bisilicate glaze may be found by -the following equation: - - SiO_{2} = 2(3Al_{2}O_{3} + 1)/2 - -Thus if the alumina content were .25 equivalent this would be expressed: - - SiO_{2} = 2(.75 + 1)/2 - -Or-- - - SiO_{2} = 3.50/2 = 1.75 equivalent - -Now in order to produce this as a mixture it would be possible to -introduce the alumina in the pure state, but pure alumina is expensive -and clay which contains alumina is cheap so that clay is generally used -to supply the alumina. Clay, however, contains silica as well, and -therefore allowance must be made for this. On referring to the formula -for kaolin, the purest form of clay, Al_{2}O_{3}, 2SiO_{2}, 2H_{2}O, it -will be seen that there is twice as much silica present in equivalence -as there is alumina and therefore .2 kaolin will contain .2Al_{2}O_{3} -and 4SiO_{2}. Subtracting, then, the 4SiO_{2} from the 1.6SiO_{2} needed -there will be 1.2 left to be supplied in the form of flint. The mixture -therefore is-- - - White Lead 1.0 × 258 = 258 - Kaolin .2 × 258 = 51.6 - Flint 1.2 × 60 = 72 - -This is a glaze of the same character as that first given except that it -no longer flows unduly from the higher places nor will it devitrify in a -long-continued fire. The alumina will have counteracted both these -evils. - -A glaze with only lead oxide as the base is not, however, desirable for -general use. The color is yellowish and the lead oxide is apt to destroy -the hue of any colors which are used with it. The available bases may be -classified under three heads. 1. The metallic oxides, lead and zinc -oxides. 2. The alkaline earths, the oxides of calcium and barium. 3. The -alkalies, potash and soda. Barium oxide is not often used and soda -cannot be used in raw glazes because there is no convenient substance -which contains it. As glazes are always ground in water only insoluble -ingredients can be employed without preparation. Potash is found in -feldspar which is insoluble and while there is a so-called soda feldspar -it can rarely be obtained of sufficient purity. - -In arranging the bases with which to compose a glaze it is desirable to -use one at least from each class, but it must be borne in mind that -however many bases are introduced the total must always be unity. This -unit is, for the sake of brevity, described as RO. For example the -following groups may be set forth: - - 1. PbO Lead Oxide .7 - CaO Calcium Oxide .3 - --- - RO 1.0 - - 2. PbO .6 - CaO .4 - --- - RO 1.0 - - 3. PbO Lead Oxide .5 - ZnO Zinc Oxide .2 - CaO Calcium Oxide .3 - --- - RO 1.0 - - 4. PbO .6 - ZnO .1 - CaO .3 - --- - RO 1.0 - - 5. PbO Lead Oxide .6 - CaO Calcium Oxide .3 - K_{2}O Potassium Oxide .1 - --- - RO 1.0 - - 6. PbO .50 - CaO .35 - K_{2}O .15 - ---- - RO 1.00 - - 7. PbO Lead Oxide .45 - ZnO Zinc Oxide .10 - CaO Calcium Oxide .30 - K_{2}O Potassium Oxide .15 - ---- - RO 1.00 - - 8. PbO .35 - ZnO .15 - CaO .35 - K_{2}O .15 - ---- - RO 1.00 - -The reason for the unit rule is that if one formula is to be compared -with another there must be a uniform basis upon which to work and, -furthermore, it makes no difference whether the silica combines with -one, two, three, or four bases, the chemical action is the same and, so -long as the sum of the bases is kept at unity, the same amount of silica -will be required. - -If two glazes be taken as an illustration this will be made clear: - - PbO .6 } - CaO .4 } - --- } Al_{2}O_{3} .2 SiO_{2} 1.6 - 1.0 } - - PbO .46 } - ZnO .12 } - CaO .28 } - K_{2}O .14 } - ---- } Al_{2}O_{3} .2 SiO_{2} 1.6 - 1.00 } - -Both of these formulae are bisilicates and each being properly fired, -will stand, without crazing, on the same body. - -The use of the formula is to give an insight into the composition of the -melted glaze. It takes no account of volatile ingredients or losses in -the fire but for this very reason it must be translated into the -substances to be weighed before use can be made of it. - -Of the ingredients given on pages 142, 143, some contain but one item of -the formula, others contain several, as in the case of kaolin already -cited. Feldspar, of the variety known as potash feldspar and named by -mineralogists, "orthoclase," is a very useful ingredient in raw glazes, -being, in fact, almost the only source of potash. The formula, page 142, -shows that a molecule or equivalent of feldspar contains one molecule of -potash K_{2}O, one of alumina Al_{2}O_{3}, and six of silica SiO_{2}. -This fact is taken into account in calculating the mixture or batch -weight. - -Base No. 5 (page 148), is as follows: - - PbO .6 - CaO .3 - K_{2}O .1 - ---- - 1.0 - -And this made up into a bisilicate glaze would be: - - PbO .6 } - CaO .3 } - K_{2}O .1 } - ---- } Al_{2}O_{3} .2 SiO_{2} 1.6 - 1.0 } - -These items are extended in a horizontal line, a space being left on one -side for the list of ingredients. - - PbO CaO K_{2}O Al_{2}O_{3} SiO_{2} - - .6 .3 .1 .2 1.6 - Addition .6 White Lead .6 - ---------------------------------------- - Subtraction .0 .3 .1 .2 1.6 - Addition .3 Whiting .3 - ---------------------------------------- - Subtraction .0 .1 .2 1.6 - Addition .1 .1 .6 Feldspar .1 - ---------------------------------------- - Subtraction .0 .1 1.0 - Addition .1 .2 Kaolin .1 - ---------------------------------------- - Subtraction .0 .8 - Addition .8 Flint .8 - ---------------------------------------- - Subtraction .0 - -Each item is thus disposed of until the list is complete. These figures -are, however, given in equivalents and each must be multiplied by the -equivalent weight of the substance used. - - White Lead .6 × 258 = 154.8 parts by weight - Whiting (calcium carbonate) .3 × 100 = 30.0 " " " - Feldspar .1 × 557 = 55.7 " " " - Kaolin .1 × 258 = 25.8 " " " - Flint .8 × 60 = 48.0 " " " - ----- - 314.3 Batch of Glaze - -These amounts are weighed out in grams, put upon the mill with half a -pint of water, and ground for about an hour. When taken off, the jar and -porcelain balls are washed with plenty of water and the washings saved. -The glaze, thus diluted, is strained through a lawn of 120 mesh and laid -aside to settle. The clear water is then siphoned or poured off and the -glaze is ready for use. - -For glazing the glaze should be as thick as cream. A finger dipped into -it should show a white coating which cannot be shaken off. The pottery -to be glazed should be first soaked in clean water until all absorption -has ceased. It is then wiped dry and plunged into the glaze bath, or, if -the piece be large, the glaze may be poured over it. The piece is gently -shaken to distribute the glaze evenly and it is then set aside to dry. -Before glazing a piece everything should be prepared. A stilt or support -upon which to set the wet glazed pottery, and a bowl of water in which -to wash the fingers so as to save all the glaze. It will be found best -to glaze the inside of the piece first. It should then be well shaken to -remove as much glaze as possible before beginning the outside. A thick -glaze inside is almost sure to run down to the bottom where it will form -a pool and perhaps burst the piece. - -Before firing, the bottom of the pottery should be carefully trimmed. -Any excess of glaze is removed and the point of contact with the table -is sponged clean. Then, when the piece is set in the kiln the bottom -will not be inclined to stick. - - -PART II: MATT GLAZES - -The texture of the matt glaze is always pleasing and the artist is not -content unless at least some of his work can be finished in this way. - -Matt glazes are not underfired glazes nor are they deadened by acid or -sand blast. They are produced in two ways. First, by an excess of -alumina which is believed to cause the formation of certain compounds in -the glaze, and, second, by an excess of silica which produces a -devitrified surface. It was mentioned in the last chapter that a glaze -free from alumina will devitrify or become dull. This is undesirable -when a glaze is intended to be brilliant but it may be controlled and -turned to advantage in the production of a certain type of matt. The -successful preparation of this silica matt is extremely difficult. In -fact, in the studio kiln it is almost impossible. These small kilns are -apt to cool with great rapidity whereas, in order to produce the silica -matt the kiln must be cooled very slowly, hours and even days of cooling -being sometimes necessary. - -The alumina matt is more simple and its texture is quite satisfactory, -being, in the opinion of some, the more pleasing of the two. - -It was mentioned in the last chapter that the best bright glazes for low -temperature work are bisilicates, having an oxygen ratio of 1:2. The -alumina matt has an oxygen ratio of about 3:4. This is secured in the -following manner. The RO content may consist of any of the bases used in -bright glazes, the proportion of each being adjusted in accordance with -the desired point of fusion. The alumina content is rather higher than -in a bright glaze and should not fall much below .3 equivalent, .35 -equivalent is even better. The silica is adjusted in accordance with the -following equation: - - SiO_{2} = 3(3Al_{2}O_{3} + 1)/4 - -Now if the alumina content be placed at .35 equivalent this would work -out: - - SiO_{2} = 3(1.05 + 1)/4 - -Or: - - SiO_{2} = 6.15/4 = 1.5375 - -But as such a complete fraction is not necessary it may be stated as -1.54 equivalent. The formula would therefore be: - - RO, Al_{2}O_{3} .35, SiO_{2} 1.54 - -The RO content should not be too fusible. Lead oxide is desirable up to -about .5 equivalent and it is an advantage to use feldspar so that -K_{2}O may be introduced. Calcium oxide is also good but zinc oxide must -be used sparingly as it is apt to suffer if overfired. The high content -of alumina necessitates a good deal of clay and as this, if used raw, -would make the glaze too plastic and cause it to crack, it is best to -calcine a part of it, thus removing the combined water and changing the -equivalent weight from 258 to 222. The calculation will then proceed as -in the case of a bright glaze. - - PbO .50 } - CaO .35 } - K_{2}O .15 } - ---- } Al_{2}O_{3} .35 SiO_{2} 1.54 - RO 1.00 } - - PbO CaO K_{2}O Al_{2}O_{3} SiO_{2} - - .50 .35 .15 .35 1.54 - Addition .50 - White Lead .50 × 258 = 129 - ---------------------------------------- - Subtraction .0 .35 .15 .35 1.54 - Addition .35 - Whiting .35 × 100 = 35 - ---------------------------------------- - Subtraction .0 .15 .35 1.54 - Addition .15 .15 .90 - Feldspar .15 × 557 = 83 - ---------------------------------------- - Subtraction .0 .20 .64 - Addition .15 .30 - Calcined Kaolin .15 × 222 = 33 - ---------------------------------------- - Subtraction .05 .34 - Addition .05 .10 - Kaolin .05 × 258 = 13 - ---------------------------------------- - Subtraction .0 .24 - Addition .24 - Flint .24 × 60 = 14 - ---------------------------------------- - Subtraction .0 - -The mix, therefore, is: - - White Lead 129 grams - Whiting 35 " - Feldspar 83 " - Calcined Kaolin 33 " - Kaolin 13 " - Flint 14 " - -This will give a silky matt glaze, nearly white, maturing at about cone -1. If a lower fusing point is desired the white lead may be increased at -the expense of the whiting or if the glaze prove too fusible the reverse -will correct it. The flint may be omitted without damage. - -The grinding of a matt glaze is of great importance. It is better to -have it too coarse than too fine. Grinding for one hour on the ball mill -should be ample and if the glaze be then strained through 120 mesh lawn -all coarse particles will be arrested. A glaze that is too fine will -crack and peel off or will curl up in the kiln. - -More than half the success of matt glazes lies in the using. It is -necessary that the coating of glaze be very thick or the true texture -will not be developed. When the glaze is taken from the mill plenty of -water may be used in order to wash the apparatus clean and to save all -the glaze. This is set aside in a deep bowl to settle. After some hours -the clear water is carefully drawn off with a siphon. - -Half an ounce of gum tragacanth is put to soak in a quart of clean -water. After twelve hours the gum will have swollen to a jelly-like -mass. This is now worked vigorously with a Dover egg-beater or in a -Christy mixer and again set aside. After another twelve hours the -operation is repeated and the solution is a clear syrup of the -consistency of thin molasses. A drop or two of carbolic acid or other -germicide should be added to prevent decomposition. This mucilage should -be prepared in advance. To the glaze batch from which the water has been -removed a tablespoonful of the mucilage is added. If more of the glaze -than the single batch has been weighed out then more mucilage will be -necessary. The mixture is to be stirred very thoroughly and it will be -found to thicken under the hand. It must be very much thicker than the -bright glaze. In fact, the thicker it is the better, only that it must -flow sufficiently so that the pottery may be covered with a smooth -coating, avoiding lumps. Matt glazes do not correct their own faults in -the kiln as bright glazes do. Every finger mark will show and, -consequently, the glazing must be done with the greatest care. The -process is the same as that described for bright glazes, except that as -much glaze as possible is left on the ware. No more shaking should be -done than will suffice to secure a smooth coating. It is well to place -the pieces upside down to dry. - -For the inside of the pieces a matt glaze may be used or a thin coat of -clear glaze at the pleasure of the worker. If the latter, care must be -taken that none of the inside glaze is allowed to run over the edge. - -In firing, the pottery is sometimes placed on a stilt but this is not -absolutely necessary. For a support a flat piece of burned clay may be -used and this should be covered with an infusible wash to prevent any -possibility of sticking. Equal parts of kaolin and flint make a good -wash. The wash is worked up with water into a slip and applied with an -ordinary brush. - - -PART III: FRITTED GLAZES - -Fritted glazes, like raw glazes, are clear and brilliant and for most -purposes the latter will suffice. Since, however, the aim of this work -is to give as complete information as may be the fritted glaze will not -be omitted. - -A fritt is a melt or compounded glass and the purpose of it is to permit -the use of certain ingredients which are not available in the raw state. -As glazes are ground in water it is essential that the substances used -be insoluble. This condition would prohibit advantage being taken of -borax, boric acid, and soda ash, if it were not for the possibility of -rendering these insoluble by the operation of fritting. - -The following is an example of a fritted glaze: - - PbO Lead Oxide .30 } - ZnO Zinc Oxide .15 } - } Al_{2}O_{2} Alumina .15 } - CaO Lime .25 } } SiO_{2} Silica 2.65 - } B_{2}O_{3} Boric Acid .40 } - Na_{2}O Soda .20 } - K_{2}O Potash .10 } - -This will be produced in accordance with the usual calculation by the -mix: - - White Lead .3 × 258 = 77 - Zinc Oxide .15 × 81 = 12 - Whiting .25 × 100 = 25 - Borax .20 × 382 = 76 - Feldspar .10 × 557 = 56 - Kaolin .05 × 258 = 13 - Flint 1.95 × 60 = 117 - -The borax contains the required amount of both soda and boric acid and -the potash is supplied by the feldspar. Borax, being soluble, must be -melted with certain other ingredients into an insoluble glass, thus: - - Fritt: - Borax 76 x 2 = 152 - Whiting 25 x 2 = 50 - Feldspar 30 x 2 = 60 - Flint 50 x 2 = 100 - --- - 362 - -These ingredients are weighed out in double quantity to guard against loss -in melting and are fused either in the kiln or in a special furnace. A good -fritting furnace is the No. 15, made by the Buffalo Dental Manufacturing -Company. The charge is put into a plumbago crucible and when melted is -poured out into water. This breaks up the fritt and renders it easy to -grind. A similar crucible may be used in the kiln but as the fritt becomes -very hard when cold and a crucible must be broken each time, the furnace -method is better. If the fritt as given prove too sluggish to pour freely, -the feldspar may be omitted, being added, of course, to the glaze mix. The -melted weight of the fritt must now be calculated. - -Borax contains in each equivalent 180 parts water. Whiting contains in each -equivalent 44 parts carbonic acid. Both water and carbonic acid pass off in -the melting, thus the 76 parts of borax will be reduced in weight to 40 -parts, and the 25 parts of whiting will be reduced to 14 parts. Spar and -flint undergo no loss. The fritt after melting will therefore be: - - Borax 40 - Whiting 14 - Spar 30 - Flint 50 - --- - 134 - -And the final mix for the glaze will be: - - Fritt 134 parts - White Lead 77 " - Zinc Oxide 12 " - Feldspar 26 " - Kaolin 13 " - Flint 67 " - -This is ground on the mill as already directed and is ready for use. - -Fritted glazes are better than raw glazes for certain classes of ware. -They are usually whiter and less easily scratched. They are, moreover, -better for use with underglaze colors and are, as a rule, more easily -melted. It is never necessary to make a fritt for the preparation of -matt glazes. - - -PART IV: RECIPES - -While the purpose of this work is not so much to put ready-made -materials into the hands of the craftsman as to enable him to work out -his own plans, it is recognized that there are some workers who lack the -training and even the patience to do this. For these, the following -recipes are given, but with the proviso that no recipe can be regarded -as perfect for all conditions. Just as an untrained cook can spoil a -dinner even when surrounded by cookery books, so the best of recipes -will fail when unskillfully treated. One must be prepared to recognize -the faults which are sure to develop and to correct them in an -intelligent manner. The previous chapters should therefore be carefully -studied, not alone for the information but because "the joy of the -working" depends greatly upon the knowledge one has of the operations -involved and a modest confidence in one's own powers. - - 1. Bright raw glaze. - Cone .06 Formula - - PbO .60 } - CaO .25 } Al_{2}O_{3} .15 SiO_{2} 1.45 - K_{2}O .15 } - - Mix: - White Lead 155 - Whiting 25 - Feldspar 55.7 - Kaolin 13 - Flint 45 - - Grind, with one-half pint of water, for one hour. - - 2. Bright raw glaze. - Cone 1 Formula - - PbO .45 } - ZnO .15 } Al_{2}O_{3} .20 SiO_{2} 1.60 - CaO .25 } - K_{2}O .15 } - - Mix: - White Lead 116 - Whiting 25 - Zinc Oxide 12 - Feldspar 83 - Kaolin 13 - Flint 36 - - 3. Bright fritted glaze. - Cone .02 Formula - - PbO .25 } - ZnO .15 } Al_{2}O_{3} .15 } - CaO .30 } } SiO_{2} 2.35 - Na_{2}O .20 } B_{2}O_{3} .30 } - K_{2}O .10 } - - Mix: - - Fritt Glaze - - Borax 114 Fritt 117 - Whiting 60 White Lead 64 - Soda Ash 10 Zinc Oxide 12 - Spar 56 Spar 28 - Flint 78 Kaolin 13 - Flint 60 - - Grind as before. - - 4. Matt glaze. - Cone .02 Formula - - PbO .50 } - CaO .30 } Al_{2}O_{3} .34 SiO_{2} 1.48 - K_{2}O .20 } - - Mix: - White Lead 129 - Whiting 30 - Spar 111 - Calcined Kaolin 22 - Kaolin 11 - - 5. Matt glaze. - Cone 7 Formula - - CaO .75 } Al_{2}O_{3} .55 SiO_{2} 2.10 - K_{2}O .25 } - - Mix: - Feldspar 139 - Whiting 75 - Calcined Kaolin 55 - Kaolin 13 - - For colored glazes add to any of the above: - - Blue: - Cobalt Oxide 3 parts - - Slate blue: - Cobalt Oxide 3 parts - Nickel Oxide 1 part - - Warm blue: - Cobalt Oxide 2 parts - Iron Oxide 1 part - - Green: - Copper Oxide 8 parts - - Blue green: - Copper Oxide 8 parts - Cobalt Oxide 1 part - - Cool green: - Copper Oxide 8 parts - Cobalt Oxide 1 part - Nickel Oxide 2 parts - - Olive green: - Copper Oxide 6 parts - Iron Oxide 4 parts - - Orange brown: - Iron Oxide 8 parts - - Red brown: - Iron Oxide 8 parts - Chrome Oxide 1 part - Zinc Oxide 3 parts - - Yellow: - Uranium Oxide 3 parts - -The coloring oxides should be weighed out and ground with the glaze. Any -of the colors may be mixed together in order to modify the hue obtained -or the amount of each coloring oxide may be varied to give a stronger or -weaker value. - - Opaque tin enamel. - Cone .02 Formula - - PbO .40 } - CaO .25 } { SiO_{2} 1.75 - K_{2}O .20 } Al_{2}O_{3} .25 { SnO_{2} .30 - ZnO .15 } - - Mixture: - White Lead 103 - Whiting 25 - Feldspar 111 - Zinc Oxide 12 - Kaolin 13 - Flint 27 - Tin Oxide 45 - - Grind, with one-half pint of water, for 45 minutes. - - -PART V: THE DEFECTS OF GLAZES - -While it may chance that body and glaze and fire are so adjusted that -faults do not develop, this state of things is rare. Besides, it is -always possible that an occasional trouble may arise, hence it will be -well to recount a few of the commonest defects with the method of cure. -A cure is not necessarily specific. There may be a complication of -causes but the remedy indicates the line along which relief will be -found. - -1. Crazing. Fine cracks appear in the glaze but do not penetrate the -body. There are many causes. The body may be underfired or overfired. In -the former case the crazing does not always appear at once and it grows -worse upon standing. In the latter case the glaze is found to be crazed -when taken from the kiln and it does not extend even after long -standing. The glaze may be underfired. In this case the lines of the -crack are broken and irregular, one often changing its direction without -meeting another crack. In all these cases the remedy is obvious. - -Crazing also occurs when both body and glaze are correctly fired but -there is an inherent disagreement in expansion. In such a case a little -flint added either to the body or to the glaze will tend to cure the -trouble but it must be remembered that the addition of flint to the -glaze is apt to render it less fusible and therefore while one craze may -be cured another may be caused. The addition of flint to the body is the -simplest remedy. - -2. Shivering or peeling. This is the reverse of crazing and is caused by -the glaze being too large for the body. It almost always appears -immediately the ware is cooled. The symptoms are that edges or convex -surfaces are pushed off and even the ware itself is shattered. The -remedy is to decrease the flint in either body or glaze. - -3. Blistering. Glazes, both bright and matt, are apt to develop blisters -at times. These may be yet unbroken when the kiln is opened or they may -have melted down to a small crater, a ring with a depression in the -center. The cause of this fault is usually to be found in the body. All -clays contain sulphur and when a clay is aged this develops an acid -which rises to the surface of the ware when dried and causes a scum. The -glaze attacks this sulphate scum and a gas is generated which boils out -and causes the blisters. If old clay blisters and new clay does not it -may be regarded as certain that this is the cause. A little barium -carbonate added to the clay will help to effect a cure. About one per -cent. is usually enough. Clay so treated, however, must not be used in -plaster molds as the barium attacks the plaster. If the cause be not -found in the clay it may exist in the glaze itself. Some glaze -ingredients contain impurities in the form of sulphates and these will -cause blisters. - -4. The glaze flows, leaving bare places. It is too fluid, add a little -clay and flint. - -5. A matt glaze burns to a bright surface. Matt glazes must be used in a -very thick coat. If too thin they will inevitably brighten. The fire may -be too high. The fire may be "reducing," that is, with insufficient air. - -6. The glaze crawls or rolls up in lumps. Notice whether the glaze is -cracked before burning. If so it will surely crawl. Too fine grinding is -usually the cause of this trouble. Too much clay in the glaze may cause -it, or a too porous body. A body which is underfired will almost -certainly cause the glaze to crawl. - -7. Pinholes appear in the glaze when cool. Too rapid cooling is the -cause. - - -PART VI: ALKALINE GLAZES - -The glory of the Persian and Egyptian blue is too alluring for potters -to withstand. Though the pursuit of this glory leads one into all kinds -of disasters and failures, the avenues of research that it opens add -unending fascination to the study. Even one beautiful glowing pot out of -twenty or more efforts is a stimulating achievement though it should not -be thought that this is the usual proportion. - -It is a continual source of astonishment that with a slight variation of -glaze formula a positive green will swim into a vibrating blue. The -addition or substitution of one substance or another in the glaze mix -may be the key to an unexpected transformation and may give the potter a -new palette of color. - -The clay body has a very positive effect on alkaline glaze both in its -composition and its color. This is especially true under a transparent -glaze where the effect is considerable since the color of the glaze -would be modified by the red or buff clay showing through. - -If, therefore, the object of the potter is to obtain a brilliant -"Persian" blue, a white clay body must be composed or a white _engobe_ -applied over the buff or red clay to hide the color. - -The Persians and Egyptians used a coarse, sandy body high in silica and -covered the roughness of the clay with a fine white _engobe_ on which -they painted their decorations in various colors. The whole was finally -covered with the transparent alkaline glaze. - -While the effect of colored clay under opaque glaze is less pronounced, -it still makes sufficient difference to be considered. - -The word _engobe_ is French and refers to a thin coating of clay, also -called a slip, laid over a colored body to change the color or over a -coarse body to give a finer texture. - -The _engobe_ is usually composed of china clay, flint, and feldspar much -as a white earthenware body is constituted but with a larger content of -flint. Ball clay may also be used but the color is not so white. - -The mixture of porcelain given on page forty will make an _engobe_ -suitable for many clay bodies. If it should crack on drying more flint -should be added. - -An _engobe_ must, of course, be put upon the unburned or green clay ware -and this should be leather hard, not dry. The body with the _engobe_ may -be burned before glazing or the glaze may be put upon the unburned ware -and the whole subjected to one fire only. - -The ingredients in alkaline glazes are soda-ash, whiting, feldspar, -flint and oxide of tin. The following is an example of a fritted glaze: - - Na_{2}O .60 } - K_{2}O .10 } Al_{2}O_{3} .10 SiO_{2} 1.30 - CaO .30 } - - Soda Ash 64 - Whiting 30 - Feldspar 56 - Flint 42 - -The entire batch is fritted and ground in a ball mill with the usual -amount of water for fritt grinding, adding a tablespoonful of gum -tragacanth mucilage to the batch after it is sieved. The glaze should be -the consistency of heavy cream when used. - -It is also possible to use an alkaline glaze in the raw or unfritted -state. This necessitates grinding by hand in a mortar, but great care -must be taken to mix the dry ingredients thoroughly before adding water -and to stir the glaze constantly while pouring in the water, otherwise -the soda-ash will cake and harden and be very difficult to break up. A -batch of glaze can be ground by hand in fifteen or twenty minutes if -done vigorously. It is then put through a 120-mesh sieve. The -consistency is of importance. If too much water has been added and the -glaze has become thin, it cannot be used successfully and should be -discarded. Unfritted alkaline glaze does not keep well when moist but -the ingredients can be ground dry and kept ready to be moistened as -needed. - -The following is an example of an unfritted alkaline glaze: - - Na_{2}O .59 } - CaO .21 } Al_{2}O_{3} .20 SiO_{2} 1.6 - K_{2}O .20 } - - Soda Ash 62 - Whiting 21 - Feldspar 111 - Flint 24 - -For color add the following oxides to a batch. - - 1. Egyptian blue, opaque--from 5 to 8 grams of black oxide of - copper--16 grams of oxide of tin. - - 2. Persian blue, opaque--from 8 to 10 grams of black oxide of - copper--16 grams of oxide of tin. - - 3. Sapphire blue--1 gram black oxide of cobalt. - - 4. Aubergine--9 grams black oxide of manganese. - -The clear glaze without any coloring oxide can be used over any of the -colored glazes. This is sometimes necessary when the colored glaze -contains such a large proportion of coloring oxide as to show black on -the surface. - -The application of alkaline glaze is very important. Any of the three -methods of pouring, dipping, and brushing can be employed. Brushing -seems to give the best results but the glaze must be put on thick, in -two or three coats, to give quality. - -The firing is interesting and important because of the varied effects it -develops from the same formula. The range of temperature is great, -varying from cone .05 to 1, developing the alkaline glaze according to -the result desired. If the biscuit is soft fired the color will be more -intense; if hard fired, the color will be much lighter in value with a -high sheen on the surface. An unfritted alkaline glaze burned to .05 -develops a soft matt finish. - -Where the color of a transparent Persian blue comes out olive green, too -little glaze has been used on the piece or the buff of the clay has -modified the color. Bubbles mean undeveloped glaze or sulphur in the -clay or fuel. Black scum shows an excess of copper in the batch, or -reduction in the fire. Sand paper surface proves too low firing or too -thin a glaze. - -If one desires to reproduce the underglaze Persian decoration the black -outlines may be drawn with a black underglaze color mixed with clay. A -little mucilage must be added to secure smooth working. The turquoise -blue is copper oxide, the dark blue cobalt, and the purple manganese. -The oxides must be diluted with white clay and used rather thin. The -Rhodian red is a finely ground red burning clay mixed with a little -flint. This red must be laid on quite thickly. It will probably be found -necessary to fire the painted decoration to about cone .03 before -glazing. The glaze may be either quite clear or slightly tinted. Another -effect may be produced by using the black outline alone under a peacock -blue or turquoise glaze. - -A great many modifications and additions to this subject will suggest -themselves to the potter as he works, and a continual study of the -masterpieces of the Persians in the museums will prove the greatest -inspiration. - - - - -CHAPTER XVI: DECORATION - - -The necessity for some kind of decoration upon the clay will always be a -point of difference amongst artists. Some prefer the simple form with a -glaze treatment only, others consider that the surface should be broken -up by design. The question will not be debated here. The aim of this -hand-book is instruction and the individuality of the worker is to be -encouraged. Directions for executing the different treatments do not -imply that these elaborations are advocated. That must be left to the -inspiration of the worker. - -Decorations may be applied upon the soft clay by incising, inlaying and -embossing; upon the dry clay or upon the burned pottery in color under -the glaze or with no glaze at all; in the glaze by the use of colors or -colored glazes; or over the glaze with colors and enamels. Each of these -methods possesses special features. Each has its own possibilities and -limitations and these should be mastered by the craftsman. - -As in the production of form a well-planned design should be prepared. -The first sketch should be made on paper or on a slab of clay but the -fitting and final arrangement are best made on the piece itself. - -Incising consists in the excavation of a shallow trench or trough on the -surface of the clay. The vase or jar having been finished should be kept -in a damp place so that the clay does not dry out completely. The design -may be made in India ink with a brush. A steel tool with a narrow chisel -end is used for cutting and care must be taken that the clay is in such -a condition of moisture as will admit of a clean trench being dug -without any rough or broken edges. The bottom of the trench need not be -very smooth but the edges should be sharp and the lines well defined. At -the same time a mechanical hardness of finish is to be avoided. The -plastic nature of the clay should be kept in mind and every surface, -though decided in character, should be soft and expressive. This result -can be secured by working over the cutting with a moist camel-hair -brush. The work must not be mopped so as to leave a woolly effect, but a -little sympathetic penciling will remove the hard lines of the tool. - -There are two possible developments of incised work. The details of the -design may be excavated or the background may be cut out leaving the -drawing in relief. - -In modeling embossments the piece should be a little softer than for -incising. It is important that in any clay work attached to a clay body -the same amount of moisture should be present in both parts. This is not -entirely possible in modeling upon forms which have already been shaped, -for if the form be as soft as modeling clay it will not bear to be -handled, while if the clay were as hard as the form it could not be -worked. A compromise is therefore necessary. The vase must be kept as -soft as possible consistent with holding its shape and the clay must be -as stiff as the working will allow. - -As little water as possible should be used and the modeling should not -be brought to its full height at once. If the clay be laid on little by -little there is much less chance of cracking. Low relief is sometimes -produced by painting in slip but here even more care is necessary. The -slip should be laid on with a brush in thin coats, each coat being -allowed to stiffen before another is applied and the whole work being -kept moist. - -An atomizer with clean water is useful in this regard. The work, being -kept on a whirler or turntable, is sprayed now and then with water and -thus prevented from becoming too hard. - -When the slip work has been raised to the desired height the surface is -tooled over so as to remove the brush marks. This is the method which -has been brought to such perfection by the French artists and by them -named _pâte-sur-pâte_. - -Modeled work is generally carried out in the same clay as that of which -the form is made and depends upon high relief for its effect. Slip -painting is usually done in a different color and if a light-colored -slip be used upon a dark clay, the latter is partially seen through the -coating in the thinnest places. This fact is made use of to accentuate -the shadow effects. - -In using one clay over another great care must be taken to insure that -the fire shrinkage is the same. The white body already given, or indeed, -any light colored clay, may be tinted by the addition of under-glaze -colors. The dry color, if sifted very fine, may be added to the plastic -clay by thorough kneading and wedging but it is better to work up the -clay into a slip and to stir in the color. The tinted slip is then -lawned two or three times and dried out on plaster or used in the slip -state as the case may be. - -A trial should be made before any important work is undertaken, both to -see that the color is right and to discover any discrepancy in -shrinkage. If a clay shrinks too much, a little ground flint may be -added. If it shrinks too little, a little ball clay will correct it. The -tint produced by the color is apt to darken in the kiln but the general -hue will be similar to that of the color used. - -For some classes of work a native red clay gives admirable results. It -may be lightened by the use of kaolin and flint and darkened by adding -burnt umber. These colors are more satisfactory than greens and blues in -clay because the brown and red tones are natural, the others are -artificial. - -If a good buff-burning clay be available, it forms the best possible -foundation for color work. Burnt umber will darken it and red clay may -be mixed with it, always having regard to the matter of shrinkage -already mentioned. - -Very pleasing effects may be produced by inlaying one clay with another. -The pattern or design is first cut out as described under incising and -then the second clay is pressed, morsel by morsel, into the excavation. -The surface is cleaned off level with the body of the piece and the -whole may be either polished or glazed. - -A plastic clay can be polished when leather hard and the finish will -remain after firing. Any tool of steel, boxwood or ivory will do the -work but a good supply of patience is needed so that the whole surface -may be uniformly treated. - -For color decoration upon the pottery, ordinary underglaze colors are -used, either upon the unburned clay or upon the burned ware commonly -called biscuit. For use upon the clay, the colors should be mixed in -water, using a little molasses, sugar, glycerine or gum arabic to make -the color flow easily from the brush. Before burning, a little glaze -should be sprayed over the work with an atomizer. Any ordinary fusible -glaze will do. It is diluted with a good deal of water as only the very -thinnest coat is necessary. The spray should not be held long in one -place or the water will flow and smear the color. If the piece be turned -slowly around the clay will absorb the water as it is applied. If this -spraying be not done the colors will be apt to rub off after burning. -Under-glaze colors are not fusible and hence they come from the fire as -dry powders. - -The work on the biscuit is much the same except that turpentine and fat -oil constitute a better working medium. When dry the spray should be -applied as before. - - - - -CHAPTER XVII: THE FIRE - - -Kilns and burning form the pivot upon which the art of the potter turns. -M. Doat has said, "A potter can no more express himself without his kiln -than can a violinist without his violin," and yet there are some who try -to make out by sending their work to some nearby pottery to be burned. -Let it be at once understood that he who finds it impossible to procure -and manage a kiln had best take to some other craft. - -Kilns are of two types, open and muffle. In the open kiln the flames -pass through the firing chamber and the ware may be exposed to their -action, as in stoneware and brick; or it may be enclosed in the -fire-clay cases, called saggers, as in the many forms of pottery, dishes -or faience. The muffle kiln is a closed chamber which is surrounded by -flames but which is not entered by them. These kilns are used in the -manufacture of terra cotta and heavy enamel wares, and the portable -kilns made for studio use are of this type. - -There are certain advantages to be gained in the use of either type of -kiln but inasmuch as the open kiln involves the use of saggers and as, -moreover, it must be properly constructed of fire-brick by a skilled -mason, it will be best to consider only the portable studio kiln.[M] - - [M] These kilns are made in several sizes by the H. J. Caulkins - Company, Detroit, Mich. - -It must not be expected that any kiln will give perfect satisfaction. -Neither built kiln nor portable kiln will do this, but either may be -relied upon to do excellent work in the hands of those who will take -trouble. A kiln of the proper size having been purchased, it must be -carefully installed. A good chimney is an absolute necessity and if one -can be built on purpose it will be best. It should be at least -twenty-five feet high with the bottom lined with fire-brick to a height -of six or eight feet. The portable kiln is set on iron legs which raise -it about one foot from the floor. This is not enough for easy work and a -platform of brick or stone, ten inches high, should be prepared. This -will greatly simplify the observation and management of the burners -which are beneath the kiln, and if it should make the inside of the -muffle hard to reach, it is easier to stand on a box to attend to the -kiln than it is to go on one's knees to the burner. - -The kiln room should have a cement floor and should be both well drained -and well ventilated. At the window there should be a stout bench where -the work of preparation may be done and at a convenient spot there -should be shelves for stilts, cones, wash, stopping and all the minor -accessories of burning. If there is room for a barrel of oil it will be -a convenience, and if the room be fire-proof the insurance company will -not object. - -The kiln having arrived it is mounted on the platform and the -asbestos-lined pipe is securely connected with the chimney. The inside -of the muffle is examined with care to see that no part has been jarred -in transit. The reservoir cans are filled with oil and a slow fire is -started. This should be allowed to burn very gently for an hour or two -in order to thoroughly dry out and season the kiln. It is a good plan to -make up a wash of equal parts of kaolin and flint and to brush this all -over the inside of the kiln. It should not be put on so thick as to -shell off from the walls but at the bottom a good coating may be laid. -This protects the walls of the kiln from the attacks of glaze and will -make them last longer. - -In order to fill the kiln economically a number of props and bats must -be provided. Some of these are sent out with the kiln but one is always -needing odd sizes and extra pieces. The props are simply legs of burned -clay; they are of any height desired and should be thick enough to stand -alone. The bats are slabs of burned clay and they rest on the props to -form shelves. The bats must be thick enough to bear the weight of any -pieces which they may be called upon to support, but they need not be -very large as two or more may be used to bridge the width and length of -the kiln. Bats and props are best made of sagger clay to which has been -added about one-third of crushed fire-brick. Broken bats serve well for -this after the first supply has been secured. This crushed burned clay, -called grog, has a very important influence upon wares which have to be -heated again and again. The size used should be about what will pass -through a 16-mesh sieve, and if the dust be sifted out through a 48-mesh -sieve, the resulting ware will be stronger. That is, only the grog which -passes a 16 sieve but lies upon a 48 sieve should be used. - -The relative proportions of clay and grog in the mix will depend -somewhat upon the nature of the clay. Three parts of clay to two of grog -by measure will be about right. - -The first charging of the kiln should be with pieces of no great -importance. The temperature in different parts must be carefully -ascertained. In order to do this a number of pyrometric cones[N] are -prepared in groups of three. - - [N] The pyrometric cones are fusible pyramids for testing heat. They - are made by Prof. Edward Orton, Jr., Columbus, Ohio. - -Let us suppose that the work is intended to be carried out at a -temperature of Cone No. 01. The numbers run both ways from this. The -higher or less fusible cones are, 1, 2, 3, 4, etc., up to 36, and the -more fusible numbers are 02, 03, etc., down to 022. If the firing is to -be to Cone 01, numbers 02, 01 and 1 are selected and set upright in a -small strip of soft clay. Eight or ten of these groups of three cones -are to be prepared for the first firing, so as to test the kiln, one -group is placed in each corner, at the bottom, and another in each -corner on a shelf, which is arranged opposite the spy-hole in the door. -In the middle of this, where it can be well seen through the hole, one -of the groups of cones is placed. They must be set so that all three -cones are visible as the kiln is being fired. - -The kiln is now filled up on both levels with pieces of pottery. To burn -an empty kiln is not a reliable test. On the first occasion the fire -should be started in the morning because no one can tell just how long -the burn will take. When this time is ascertained it is best to start -the fire so that the kiln will be finished by early evening. The cooling -then takes place at night and there is no temptation to open the door -too soon. - -The fire is started slowly and the flow of oil is gradually increased as -the muffle begins to glow. The work here needs practice, nerve and -judgment. A good deal of smoke will be seen at the chimney at first but -this should disappear as the kiln grows red. If the fire be urged too -strongly at the beginning fuel will be consumed to no purpose, the only -result being the choking of the flues with carbon. As the red becomes -visible through the spy-hole, more oil may be supplied, but notice must -be taken that the smoke at the chimney does not increase. The ideal -firing is where there is no smoke but this cannot be reached until the -kiln is hot enough to cause the smoke to burn. - -Persons who have burned kilns for overglaze work will find the method of -burning pottery very different. Instead of a fire brought as rapidly as -possible to the finishing point, there must now be a slow soaking burn -in which the heat shall have time to saturate the ware. - -The cones in front of the spy-hole must be observed from time to time -and presently as the kiln reaches a bright cherry red, number 02 will -begin to bend at the tip and will gradually arch over until the point -touches the shelf upon which the cones stand. By this time number 01 -will have begun to bend and when the point of this has touched the -shelf, the firing is over and the oil is shut off. - -It requires some resolution to leave a kiln until morning but it is -conducive to early rising anyway. The kiln need not be quite cold but it -will help the kiln itself to wear better and the pottery will be better -if nothing is done until everything can be handled without gloves. - -The cones are now taken out and a diagram is made of each level with the -bend of each cone accurately drawn. This diagram should be mounted and -hung on the wall for reference. It is not well to trust to memory. It -will probably be found, in the type of kiln we are discussing, that the -cones on the bottom have bent further than those on the shelf. That is, -the bottom is somewhat the hotter. - -The variation in the kiln is not necessarily a disadvantage. It may be -utilized in burning wares of different kinds. For example, if the bottom -prove much the hotter, the biscuit ware may be placed below and the -glazed pieces on the shelf. In such case the shelf itself should be -washed with a good coating of clay and flint in order to protect it from -casual drops of glaze. - -If a number of small pieces are being made, more than one shelf should -be set up. The legs may be just a little taller than the tallest of the -small pieces, but the art of placing or filling a kiln economically -consists in making selection of pieces which fit well together both as -regards height and shape. Thus, pieces which are large at the base may -be dovetailed in with others of which the base is smaller than the upper -part. In the case of clay ware the pieces may be set close together or -even piled one upon another. There is no danger of sticking unless the -ware is burned to complete vitrification. The glazed pieces must not, of -course, touch each other. - -It will be seen, from these instructions, that there should be a good -assortment of wares from which to select. Economical firing cannot be -managed if a burn be attempted whenever a piece is ready, and patience -must be exercised so as to fill the kiln to advantage. - -It is important that anyone attempting to burn a kiln should have some -understanding of the phenomena of combustion. Many things occur in the -firing which, without such an understanding, are not easily explained -but which become perfectly clear when considered in the light of simple -chemical science. - -Combustion means oxidation or a combination between the elements of the -fuel, principally carbon and hydrogen, and the oxygen of the air. This -combination is a chemical action and as it proceeds heat is liberated. -With a given amount of a specific fuel and a given amount of air there -is always the same amount of heat, but the rate at which this heat is -given off varies with the time occupied in the operation. Heat may be -generated slowly which means a low temperature, or the same volume of -heat may be generated rapidly, occupying a much shorter time and -developing a higher temperature. From these statements it will be seen -that there is a difference between heat and temperature; heat means -volume, temperature means intensity. Thus the temperature derivable from -a given amount of fuel depends upon the rapidity with which it is -burned. - -Combustion may be either complete or incomplete. In the former case -enough air is supplied to oxidize all the fuel with, usually, some -excess. The contents of the kiln are then bathed in the heated oxygen -and the condition of the burning is called oxidizing. When the -combustion is incomplete, on the other hand, there is a deficiency of -oxygen. The kiln is charged with hot carbonaceous gases and smoke, and -these, being hungry for oxygen, will abstract it from any substance -which may be present. This condition is called reducing because the -compounds which exist in clay or glaze are deprived of oxygen and thus -reduced to a lower state of oxidation. - -In burning a kiln one should be able to produce either of these -conditions at will because there are certain wares which require one or -the other in order to secure the best results. To put the matter in a -nutshell, oxidizing conditions are induced by a strong draft and open -flues, reducing conditions are obtained by closing the air inlets and -using a liberal amount of fuel. - - - - -CHAPTER XVIII: HIGH-TEMPERATURE WARES - - -The subject of "Grand Feu Ceramics" has been so ably developed by M. -Taxile Doat in his admirable treatise[P] that it will be unnecessary to -go deeply into the matter, but in order that the reader may be aware of -what is involved, some description of the technique will be given. - - [P] Keramic Studio Publishing Co., Syracuse, N. Y. - -Hard-fired wares are divided into two classes, porcelain and stoneware. -The latter is called by the French, "Grès," an abbreviation of the name -"Grès de Flandres," the stoneware made in the low countries in the -sixteenth century. Both these wares are, technically, once fired, that -is, the body and glaze come to maturity at one and the same burning. The -biscuit ware is often given a low burn at first in order to facilitate -handling, but this leaves the body very porous and is in no sense a -maturing fire. The glaze is laid upon this porous ware, or upon the -unburned clay if preferred, and then comes the high fire or "Grand Feu" -of the French. - -A mix for a porcelain body has already been given but if the ceramist -means seriously to attack the porcelain problem he will have to do some -experimental work for himself. The Georgia kaolin mentioned in the -recipe on page 40 is a good, plastic clay but it is slightly off color. -It may be necessary to improve the color by the use, in part, of another -kaolin such as the Harris clay from North Carolina.[Q] - - [Q] The Harris Kaolin Company, Dillsboro, N. C. - -Furthermore, in the preparation of a fine porcelain it is necessary to -grind the whole mix upon a mill. The mill used for glaze grinding will -answer every purpose and care must be taken that the grinding, while -carried far enough, be not too long continued. A certain amount of fine -grit in the body mass is necessary but only by constant practice can the -right point be reached. In making these experiments each step should be -faithfully noted in a handy book. The amount of water to a given weight -of clay and the duration of the grinding should be accurately observed -and written down. It is most unwise to trust to memory. - -The process of casting may be used for porcelain as already described, -but the very best of workmanship is necessary. The hard fire to which -the porcelain is subjected reveals every error which has occurred in the -making. The same thing applies to wheel work. Not only is great skill -required in order to shape the tender porcelain clay on the wheel but -the very essence of the porcelain is its lightness, to produce which by -craftsmanship a long and arduous course of training must be endured. - -Stoneware is free from many of these difficulties and, consequently one -who attempts the conquest of high-temperature wares is advised to begin -with this. Stoneware clay need not be a mixture. There are many clays -which can be used for the manufacture of grès with no more preparation -than that laid down for common clays.[R] It sometimes happens that a -clay will need the addition of a small quantity of flint or spar but -this does not amount to a difficulty. - - [R] Stoneware clays may be procured from The Western Stoneware Company, - Monmouth, Ill.; H. C. Perrine and Sons, South Amboy, N. J. - -Stoneware does not present the same manufacturing difficulties as are -found in porcelain. The clay is quite plastic and can be easily shaped -on the wheel; casting is scarcely a suitable process for this ware. The -essence of stoneware is strength and virility, just as that of porcelain -is lightness and grace. Each ware has forms suited to itself and it is a -mistake to depart from these essential characteristics. - -After shaping and drying the technical manipulation of both wares -proceeds along the usual lines. The first fire is at a very low -temperature. The melting point of silver (cone 010) is enough in nearly -every case. This leaves the ware in a soft and porous condition but hard -enough to resist the action of water. The process of glazing has already -been described but the composition of the proper glazes differs from -that of low temperature glazes. - -Porcelain is always burned in a reducing fire; stoneware may be burned -either reducing or oxidizing. The temperature at which the glaze is -burned is very high, it must be, in fact, the maturing point of the body -itself. - -The simplest form of porcelain glaze is that represented by the formula-- - - K_{2}O .3 } - CaO .7 } Al_{2}O_{3} .5 SiO_{2} 4.0 - -Which is carried out in the following mixture: - - Feldspar 167 - Whiting 70 - Kaolin 52 - Flint 108 - ---- - -The glaze is ground for use. - -The same glaze will also serve for stoneware but it will burn to a -brilliant surface whereas stoneware is better when finished with a matt -texture. - -The following is a stoneware matt glaze: - - K_{2}O .3 } - CaO .7 } Al_{2}O_{3} .7 SiO_{2} 2.6 - -Of which formula the mixture is-- - - Feldspar 167 - Whiting 70 - Calcined Kaolin 66 - Raw Kaolin 26 - ---- - -The porcelain glaze is at its best when uncolored. The matt glaze will -be more interesting when used as a colored coating. - -The following are a few suggestions for colored matt stoneware glazes. -To the glaze batch, 329 parts, add: - - For blue: - Cobalt Oxide 2 parts - Nickel Oxide 1 part - Ground Rutile 10 parts - - For brown: - Iron Oxide 6 parts - Nickel Oxide 3 parts - Ground Rutile 10 parts - - For green: - Chrome Oxide 2 parts - Cobalt Oxide 1 part - Iron Oxide 4 parts - - For dark red: - Iron Oxide 10 parts - Chrome Oxide 2 parts - Zinc Oxide 6 parts - -Rutile has not before been mentioned. It is a crude oxide of titanium -and is exceedingly useful in high temperature work for producing odd, -mossy and crystalline effects. - -These mixtures make no pretense to be complete, they are given as -suggestions only because if the artist-potter is to be successful he -must be prepared to compound glazes which are the expression of his own -individuality. - -For burning high-temperature wares the kilns already described may be -used but upon purchasing it should be stipulated that the kiln is to -stand burning up to cone 11 or 12. Successful porcelain can be made at -cone 10 but better results are secured at cone 12, though, of course, -the wear upon the kiln is proportionately greater. Stoneware requires a -burn of about cone 9, higher or lower according to the clay used but -fine results must not be expected below cone 7 nor is it necessary to go -higher than cone 10. - - - - -CHAPTER XIX: CLAY-WORKING FOR CHILDREN - - -One of the modern developments of clay-working is the use of it in -elementary and high schools as a branch of manual training. In this, -clay meets the most exacting needs of the work for it affords a perfect -means of self-expression. Other arts interpose between the pupil and his -material a series of tools or appliances, more or less elaborate, which -constitute a barrier to the personal touch. Clay presents no such -obstacles. The ten fingers are all the tools that are necessary at the -beginning and, consequently, the personal equation in clay-working is -remarkably high. - -In the kindergarten the children take to clay work as little ducks to -water and the interest is never lost. In this way, clay, instead of -adding to the labors of a teacher already overburdened by a plethora of -subjects, constitutes a real relief. The work is so interesting that it -moves along of itself and all that is needed is intelligent direction. - -It is, of course, necessary that anyone attempting to teach clay-working -to children should have a knowledge of methods and principles. The -essence of power, especially in teaching, is reserve, but there is great -danger in expecting too much from small heads and hands. In the early -exercises the skill of the teacher should even be employed to conceal -her art. It is a mistake to place before elementary pupils work which is -far beyond their reach. Let the teacher make before the class something -which they themselves can do if they try and they will be encouraged to -greater effort. - -A small cylinder is a suitable beginning exercise for several reasons. -The form is definite and the result may therefore be easily criticized -by the children themselves, the size of the piece may be readily adapted -to the small fingers and the simplicity of line enables the attention to -be concentrated upon the manipulation of the clay. - -This cylindrical form may be made more interesting by the addition of -little feet or handles; by a simple line border incised along the upper -edge; or by dividing the surface into well-spaced panels. The planning -of the cylinder itself is a good exercise in rectangle proportion. - -In order to enable the pupils to turn their work from side to side each -one should be provided with a piece of paper or cardboard the size of -the base of the pottery. The building is started upon this and, managed -in such a way, the clay does not stick to the table. - -When the idea of pottery building, either by coils or by pieces welded -together, has been grasped, the children should be taught to think in -the solid. There is almost always a difficulty in making children see -that an outline drawing and a solid form may be alike in meaning. The -teacher should draw upon the blackboard a simple jar in elevation, the -plan, of course, will be a circle. The same thing is then made in clay -by both teacher and children and the results are compared with the -drawing. This will lead to the designing of the forms in outline by the -children themselves. These designs should be made the exact size of the -proposed pottery and if the outline be carefully cut out the line of the -paper may be applied to the work as a template. By such means the -children are led to produce accurate lines in the clay and control over -the material is secured. - -There is always a temptation, when the clay sags or loses shape, to -diverge from the original idea and to allow the material to shape -itself. This inevitably leads to slovenly work and should be resisted -from the first. The paper template helps to correct such an impulse and -the pupil presently finds that the clay can be successfully controlled -if enough trouble be taken. There is much interest too in the cutting of -pottery forms from folded paper. A number of these forms may be pinned -on a screen and the children led to select the best in line and -proportion. Too much emphasis cannot be laid on the necessity for -showing the children fine examples of pottery, both ancient and modern. -The more primitive types, where the form and the decoration are so -perfectly adapted to each other and to the material, are full of -inspiration for the child potter as well as for the adult. When one is -fortunate enough to be near a museum, many illustrations will be found, -but good photographs or drawings are available for almost everyone. -Constant comparison and the exercise of choice will lead to a -development of taste, which must affect the child whether he later -becomes a producer or a consumer. - -A flower holder is a good problem. It is a solid piece of clay two or -three inches in diameter and an inch thick. This may be round or square -in form and may have simple modeled decoration added to it. Quarter inch -holes are pierced at regular intervals, in fact, they themselves should -form part of the design. For the older children a shallow bowl of good -line with a flower holder to fit is an interesting problem. Other good -problems, which may be made more or less difficult according to the -grade in which they are given, are rose jars, bread and milk bowls, -incense burners, cylindrical jars, square fern dishes, candlesticks and -small lamp bases. - -When working out decoration for pottery forms, it is well to have the -children make their designs with the modeling tool upon the clay itself. -If a piece of soft clay be rolled out flat upon the table it affords the -best possible medium for making clay designs. The pupil is at once put -in touch with the possibilities and limitations of the material. A -drawing made upon paper may have to be entirely changed before it is -suitable for use on clay. The soft surface can be smoothed over as often -as necessary and a new sketch made until a design is approved for -application to the pottery itself. In the chapter on decoration will be -found suggestions for clay treatment. - -The making of tiles affords an interesting application of the principles -of design, but the instructions in the chapter on tile should be -followed in order to insure a workman-like product. If it is possible to -use plaster, the making of a decorated tile from which a mold can be -made and other tiles pressed is a good problem. Animal forms lend -themselves to the decoration of such tiles and are always interesting to -children. - -While these chapters are especially devoted to ceramics in the sense of -burned and glazed pottery a few words upon modeling as related to school -work may be added here. Imitative modeling from cast or copy with its -development of animal and figure modeling, both from life and from -memory, is valuable in the acquirement of the power of manipulation and -control as well as in the cultivation of observation, imagination and -memory. In the best regulated schools the work of the grades is often -correlated in the study of some phase of human life. Facts are grouped -around some epoch or event in history or some country or clime in -geography. The children take up the clay while their minds are full of -the current subject and nothing more natural than that they should -illustrate the story by models. - -Such work is to be thoroughly commended as truly educational, though it -does not fall strictly within the field of pottery and a few suggestions -may therefore be in order. - -The modeling of animals or people for the sand table is full of interest -for the younger children. Such stories as "The Three Bears," "Chicken -Little" and "The Little Red Hen" immediately suggest themselves. For -children of about the fourth grade "Alice in Wonderland" offers a most -fascinating array of models. "The White Rabbit," "The Duchess," "The -Mock Turtle," "The Mad Hatter," grotesques of all sorts, seem a natural -outcome of this illustration work and the wise teacher will see the -possibility for developing the imagination in the modeling of mythical -creatures, such as dragons and gnomes, and in the personification of the -elements. There is also an unlimited fund of material in the tales of -knighthood and of fairyland. - -With the older children, simple principles of design and composition -should be suggested. A paper weight is an interesting problem demanding -the adaptation of form to space. - -Many of these things may be modeled in clay, dried and painted with -water color or one of the patent modeling clays which set like cement -may be used. If no supports have been left in the model it may be fired -when thoroughly dry. - -Some of the best projects for sand table work involving modeling are -Eskimo Life, Indian Life, Farm Life, The Circus, and Fairy Tales. -Generally a suggestion is all that is necessary to call forth the most -original conceptions and once started the children will soon far -outstrip the teacher. - - - - -INDEX - - - A - - Alhambra Vase, 16 - Armenian Bole, 15 - - - B - - Ball-Clay, Tennessee, 40 - Bases for Glaze, 143 - Berlin Porcelain, 28 - Bisilicate Glaze, 145, 146 - Black Surfaced Ware, 13 - Blistering of Glazes, 166 - Building, Clay for, 69 - Building, Faults in, 72 - Building, Methods of, 70, 71 - Built Pottery, 10, 68 - Burning Tiles, 139 - - - C - - Case for Mold-making, 58 - Casting, 129 - Casting, Slip for, 129 - Castor Ware, 13 - Children, Pottery for, 194 - Chinese Porcelain, 23 - Clay, Colored, 36 - Clay, Crude, 9, 37 - Clay, Decoration in, 173 - Clay, for Building, 69 - Clay, for Tiles, 134 - Clay, Preparation of, 37 - Colored Glazes, 24, 143, 163 - Colors, Underglaze, 25, 143, 177 - Combustion, 186, 187 - Cones, Pyrometric, 182 - Copenhagen Porcelain, 27 - Crawling of Glazes, 166 - Crazing of Glazes, 165 - Cups and Saucers, 124 - - - D - - Decoration, 173 - Decoration of Tiles, 137 - Defects of Glazes, 164 - Devitrification, 152 - - - E - - Earthenware, Mixture for, 40 - Engobe Ware, Oriental, 15 - - - F - - Famille Rose, 24, 26 - Famille Verte, 24, 26 - Feet for Vases, 105 - Firing the Kiln, 179 - Fitness in Design, 3, 4, 7 - Flowing of Glazes, 145, 166 - Form and Weight, 7 - Fritt for Glaze, 158 - Fritting Furnace, 159 - - - G - - Glaze, Bases for, 148 - Glaze, Bisilicate, 144, 145 - Glaze, Calculation of, 150 - Glaze, Fritt for, 158 - Glaze, Pinholes in, 167 - Glaze, Porcelain, 191 - Glaze, Recipes, 160 - Glaze, Stoneware, 191, 192 - Glazes, Blistering of, 166 - Glazes, Clear, 141, 161 - Glazes, Colored, 143, 163, 192 - Glazes, Crawling of, 166 - Glazes, Crazing of, 165 - Glazes, Defects of, 164 - Glazes, Flowing of, 145, 166 - Glazes, Grinding, 151, 155 - Glazes, Ingredients for, 142, 143 - Glazes, Matt, 152, 191 - Glazes, Nature of, 141 - Glazing, 140 - Glazing Tiles, 137, 138 - Grès de Flandres, 21 - Gum Tragacanth, 156 - - - H - - Hard Porcelain, 23, 189 - High-temperature Wares, 188 - - - I - - Ingredients for Glazes, 142, 143 - - - J - - Jars for Storing Clay, 41 - - - K - - Kiln, Firing the, 179 - Kiln, Portable, 180 - Kilns, 179 - - - L - - Lawns, Silk, 41 - Large Pieces, 107 - - - M - - Matt Glazes, 152 - Methods of Making Tiles, 135, 136 - Molds for Plates, 62, 63 - Molds for Vases, 52 - - - O - - Oriental Engobe Ware, 15 - Ox-blood Red, 24, 26 - Oxidizing Fire, 187 - Oxygen Ratio, 145 - - - P - - Pâte-sur-pâte, 14, 175 - Pieces, Large, 107 - Pinholes in Glaze, 167 - Plaster-of-Paris, 45 - Plaster Dishes, 46, 47 - Plaster Head for Wheel, 65, 78 - Plaster, Setting of, 45 - Porcelain, Berlin, 28 - Porcelain, Copenhagen, 27 - Porcelain Glaze, 191 - Porcelain, Hard, 23, 189 - Porcelain, Mixture for, 40 - Porcelain, Sevres, 25 - Potter's Wheel, 74 - Pottery, Built, 9, 68 - Pottery, for Children, 194 - Pottery, White-coated, 14, 168 - Props and Bats for Kiln, 182 - Pyrometric Cones, 182 - - - R - - Recipes for Glazes, 160 - Reducing Fire, 187 - - - S - - Salt-glazing, 21 - Saucers, Cups and, 124 - Shivering of Glazes, 165 - Size, Mold-makers', 44 - Slip, 38, 39, 129 - Slip for Casting, 129 - Slip-painting, 175 - Stoneware, 21, 188, 190 - Stoneware Glaze, 191 - - - T - - Tennessee Ball-clay, 40 - Tiles, 133 - Tiles, Burning of, 139 - Tiles, Clay for, 134 - Tiles, Decoration of, 137 - Tiles, Glazing, 137, 138 - Throwing, 77 - Tin Enamel, 164 - Tragacanth, Gum, 156 - Turning Tools, 100 - - - U - - Underglaze Colors, 143, 177 - - - V - - Vase Forms, Turning, 49-52 - Vases, Feet for, 105 - Vases, Molds for, 52 - - - W - - Weight and Form, 7 - White-coated Pottery, 14, 168 - - - - -[advertisement] - -Books for the Craftsman - - ¶ We can always supply any book on the Manual Arts--whether it is - issued by us or by any other publisher. - - ¶ Our stock of these books is complete and our facilities for - filling your orders promptly and carefully are unsurpassed. - Send your inquiries to us. - - ¶ A request will bring our various catalogs. - -D. 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