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diff --git a/40411-0.txt b/40411-0.txt new file mode 100644 index 0000000..bfe8bae --- /dev/null +++ b/40411-0.txt @@ -0,0 +1,4651 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 40411 *** + +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. VAN NOSTRAND CO., INC. + +8 Warren Street New York City + + + + + +End of the Project Gutenberg EBook of The Potter's Craft, by Charles F. Binns + +*** END OF THE PROJECT GUTENBERG EBOOK 40411 *** |