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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..13bb1da --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #66082 (https://www.gutenberg.org/ebooks/66082) diff --git a/old/66082-0.txt b/old/66082-0.txt deleted file mode 100644 index 744e94b..0000000 --- a/old/66082-0.txt +++ /dev/null @@ -1,1645 +0,0 @@ -The Project Gutenberg eBook of The Mysterious Box, by Bernard Keisch - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: The Mysterious Box - Nuclear Science and Art - -Author: Bernard Keisch - -Release Date: August 18, 2021 [eBook #66082] - -Language: English - -Character set encoding: UTF-8 - -Produced by: Stephen Hutcheson and the Online Distributed Proofreading - Team at https://www.pgdp.net - -*** START OF THE PROJECT GUTENBERG EBOOK THE MYSTERIOUS BOX *** - - - - - THE MYSTERIOUS BOX: - Nuclear Science and Art - - - by - Bernard Keisch - - - - - Contents - - - The Mysterious Box 2 - How Old Is a Painting? 11 - Who Was the Artist? 24 - Other New Tools for Art Authentication 36 - One Mystery Solved 42 - Reading List 44 - - United States Atomic Energy Commission - Office of Information Services - Library of Congress Catalog Card Number: 70-606040 - 1970; 1974 (rev.) - - -The Author - - [Illustration: Bernard Keisch] - -Dr. Bernard Keisch received his B.S. degree from Rensselaer Polytechnic -Institute and his Ph.D. from Washington University. He is a Senior -Fellow with the Division of Sponsored Research of Carnegie-Mellon -University in Pittsburgh. He is presently engaged in a project that -deals with the applications of nuclear technology to art identification. -This is jointly sponsored by the U. S. Atomic Energy Commission and the -National Gallery of Art. Previously he was a nuclear research chemist -with the Phillips Petroleum Company and senior scientist at the Nuclear -Science and Engineering Corporation. He has contributed articles on art -authentication to a number of journals. For the AEC, in addition to this -booklet, he has written _The Atomic Fingerprint: Neutron Activation -Analysis_, _Secrets of the Past: Nuclear Energy Applications in Art and -Archaeology_, and _Lost Worlds: Nuclear Science and Archaeology_. - - - - -Nuclear energy is playing a vital role in the life of every man, woman, -and child in the United States today. In the years ahead it will affect -increasingly all the peoples of the earth. It is essential that all -Americans gain an understanding of this vital force if they are to -discharge thoughtfully their responsibilities as citizens and if they -are to realize fully the myriad benefits that nuclear energy offers -them. - -The United States Atomic Energy Commission provides this booklet to help -you achieve such understanding. - - - - -The Cover - -This painting, originally believed to be the work of the Dutch artist -Frans Hals (1580-1666), is a fake. Measurements of the naturally -radioactive isotopes, polonium-210 and radium-226, in lead white from -the paint proved that it was no more than 50 years old. - - [Illustration: _A Van Meegeren forgery of a Vermeer._] - - - - - The Mysterious Box - - -The New Jersey sun was high overhead and the day was hot. The three boys -walking along a deserted stretch of beach didn’t mind because they were -barefoot and in their swimsuits. Occasionally they would dash in and out -of the surf to cool off. - -Suddenly Martin let out a yell as his toe hit something hard hidden in -the sand at the water’s edge. A moment later Bill and Harley were -helping Martin dig out a large wooden case. It was heavy, well built, -tightly sealed, and had foreign words written on it. - -“Maybe it’s a pirate treasure chest,” said Martin, who was almost eight -and had just read _Treasure Island_ for the first time the week before. - -“You’re crazy,” said Harley, who, nearly ten, was much older and wiser. - -Bill, going on twelve, thought aloud, “It must be something worthwhile; -maybe we can sell it and buy those model rockets we wanted.” - -The three boys soon found that they couldn’t open the box and that it -was too heavy to drag along the sand easily. - -“Martin,” said Bill, “get Dad while Harley and I stand guard.” - -Two hours later the box was at their house and everyone in the family -was trying to read what was written on it. About all that was readable -was a large “U” followed by what appeared to be two numbers. Some of the -other marks looked like old German script and there was a date, 1945. - -“You know,” said Bill, “I bet that came from a World War II German -submarine that our Coast Guard or Navy sank.” - -“Let’s open it up!” said Harley as Martin ran to get the screwdrivers. - -Inside they found a thoroughly waxed carton that they had to cut open. -Everyone held their breath as their father lifted the top. - -“Nothing but a bunch of pictures,” said Martin who was still hoping for -pirate treasure. - -“Paintings can be worth a lot of money,” said Dad, “thousands or even -millions of dollars.” - -“Well then we’re rich!” yelled Harley and Bill together. - -“Not so fast,” said Dad. “First of all, we don’t know if the paintings -are really valuable. Also, it looks like these might be part of the art -treasures that the Nazis stole from the countries they conquered in -World War II. Maybe someone was trying to get them by submarine to a -neutral country, like Argentina, just before the end of the war, and the -sub was sunk. If they are real and stolen, they’ll have to go back to -their rightful owners. But cheer up, maybe there’s a reward.” - -“How do we collect it?” asked Bill. “If the Nazis grabbed them, aren’t -they real for sure?” - -“Not necessarily,” Dad continued. “The Nazis were fooled sometimes by -people who sold them fakes. There was one painting that Hitler’s -sidekick, Göring, bought that was supposed to be a 17th century painting -by Vermeer, a Dutch painter. Because Vermeer’s work is so valuable, it’s -usually impossible to buy one for any amount of money. - -“Vermeer is regarded as a national hero by the Dutch. The matter was -investigated and the painting traced to Han Van Meegeren, a modern Dutch -painter who had only a fair talent. When Van Meegeren realized he might -be charged with treason by the Dutch for selling a Vermeer to the Nazis, -he confessed that he had painted it himself. He also confessed that he -had painted other forgeries that fooled some of the experts and were -sold for a lot of money. - -“Many people, however, thought Van Meegeren was only lying to save -himself from the charge of treason, and the whole thing had to be -decided by a committee of scientific art experts appointed by a court of -law. Using the methods that were then available, the experts showed that -Van Meegeren had done a remarkable job of forgery and they were -convinced that he had been telling the truth about painting those -pictures. - -“At the time, the important ways the experts used to examine a painting -included studying the work with X rays, which could show another -painting underneath, analyzing the pigments (or coloring materials) used -in the paint, and examining the painting for certain signs of old age. - - [Illustration: _Han Van Meegeren listens to the evidence at his - trial in Amsterdam. In the background is “The Blessing of Jacob”, - which was sold in 1942 as the work of Vermeer._] - - [Illustration: _An authentic Pieter de Hooch work, “The Card - Players”, painted in the 17th century._] - - [Illustration: _A forgery of a Pieter de Hooch picture painted in - the 20th century by Han Van Meegeren._] - - [Illustration: _“Head of Christ” by Van Meegeren._] - -“Van Meegeren was well acquainted with these methods. He scraped the -paint from old paintings that weren’t worth much just to get the canvas -and tried to use pigments that Vermeer would have used. He knew that old -paint was very, very hard and impossible to dissolve; so he cleverly -mixed a chemical (phenolformaldehyde) into his paint, and this hardened -into Bakelite when he heated the finished painting in an oven. - -“For some of the paintings, Van Meegeren became careless and the experts -did find traces of a modern pigment (cobalt blue) in the paint. They -also found the Bakelite. For one or more paintings, Van Meegeren did so -well that, in spite of all this evidence, a few people still weren’t -convinced that these paintings were painted by Van Meegeren and not by -Vermeer.” - -Bill, who by this time was bursting with questions, interrupted, “You -mean they still aren’t sure about some of those paintings after 25 -years? Aren’t there better ways of telling whether a painting is genuine -or not? You’re a scientist. Can’t scientists like you do something about -it now?” - -“Yes, recently a method was developed to settle just such a question. -It’s based on measurements of natural radioactivity in one pigment that -all artists used hundreds of years ago. And the method was applied to -some of the Van Meegeren paintings including the best one of them all.” - -“How did it come out?” asked Martin. - - [Illustration: _An X ray of part of the Van Meegeren forgery, - “Christ and His Disciples at Emmaus”. In the white circle are traces - of paint from the original painting that Van Meegeren scraped off to - obtain the old canvas. When the painting was believed to be a - genuine Vermeer, it was sold for about $300,000._] - - [Illustration: The complete painting.] - - [Illustration: _A Van Meegeren forgery of a Vermeer._] - -“How does it work?” asked Harley. - -“You mean paintings are radioactive?” exclaimed Bill. - -“Can we do it to the paintings we found?” asked all three together. - - - - - How Old Is a Painting? - - -“One question at a time. I’ll tell you how the method works and what it -does if you’re really interested.” - -“We’re interested! We’re interested!” chorused the boys. - -“In the first place, this method works only in certain cases of -suspected forgery. Over the last 50 or 100 years, a number of paintings -have turned up that seemed, even to the best art experts, to be several -hundred years old. Some of these were genuine, and some were painted by -forgers who could not resist the high prices paid for works of art. The -National Gallery of Art, in Washington, D. C., thinking that there might -be a way of detecting these forgeries, gave its support to a group of -scientists who developed a method for this purpose. - -“To understand how the method works, you need to know a little about how -radioactive atoms disintegrate to form atoms of other elements. In this -case we are interested in the natural radioactivity that occurs in -certain rocks. As a matter of fact, in almost all rocks in the earth’s -crust there is a certain small quantity of uranium.” - -“I thought uranium was rare,” interrupted Bill. - -“It is, but we’re talking about such small quantities that its difficult -for scientists using the most sensitive equipment to detect it. The -uranium in the rock decays to another radioactive element and that one -decays to another, and another, and another, and so forth, in a series -of elements that results in lead, which is not radioactive. In this -series are two radioactive elements, radium and a radioactive isotope of -lead, that help us to date paintings. To understand this, we must first -understand how radioactive elements decay. - -“All radioactive elements have what is known as a ‘half-life’; that is, -in a certain period of time, half of the element disintegrates to -another form. In another equal period of time, half of what is left -disintegrates, and then half again, and so on. In the case of the -uranium, which starts the series I am describing, the half-life is over -4,000,000,000 years. Because of its long half-life there is plenty of -uranium around and will be for a long, long time. On the other hand, -radium, which I mentioned a moment ago, has a half-life of only 1600 -years. In 1600 years, half of it would be gone, and in another 1600 -years half of that would be gone, and so on. - -“The radioactive lead that we’re interested in has a half-life of only -22 years. This means that if you start with a small quantity of this -radioactive isotope of lead, which is called lead-210,[1] then in only a -few hundred years it would have disappeared. However, in rock, where -there is uranium, the uranium keeps feeding the elements following it in -the series, so that as fast as they decay they are reproduced by the -element before them.” - - [Illustration: _The Uranium Series. In this simplified diagram, the - double vertical arrows represent alpha radioactivity and the single - slanted arrows represent beta radioactivity. The times shown on the - arrows are the half-lives for each step._] - - Uranium-238 - ⇓^α 4½ billion years - Thorium-234 - ↓^β 24 days - Protoactimum-234 - ↓^β 1⅕ minutes - Uranium-234 - ⇓^α ¼ million years - Thorium-230 - ⇓^α 80 thousand years - Radium-226 - ⇓^α 1600 years - Radon-222 - ⇓^α 3⅘ days - Polonium-218 - ⇓^α 3 minutes - Lead-214 - ↓^β 27 minutes - Bismuth-214 - ↓^β 20 minutes - Polonium-214 - ⇓^α less than one second - Lead-210 - ↓^β 22 years - Bismuth-210 - ↓^β 5 days - Polonium-210 - ⇓^α 138 days - Lead-206 - (Not Radioactive) - -“I don’t quite understand how that works,” said Harley. “What do you -mean ‘it keeps feeding it’?” - -“Well, think of a series of lakes connected by waterfalls. At the top, -the highest lake has an enormous supply of water. Following the -waterfall coming out of the lake you find a smaller lake and then maybe -a medium-sized lake, and after another waterfall, a smaller lake, then a -tiny lake, and so on. - -“As long as that big lake on top is full or nearly full, all the other -lakes, whether they are small or medium-sized, will still be getting -water as fast as it pours out. But if you cut off the supply of water -from the upper lake to the next lake, then the smaller lakes will in -time run dry. The same thing works with the radioactivity. In this -series headed by uranium, as long as uranium is present all the other -elements below it are kept supplied so that they don’t run out.” - -“I understand that,” said Bill, “but how do we use that to date a -painting?” - -“One of the pigments used by artists for over 2000 years is known as -lead white and it is made from lead metal. The lead metal in turn is -extracted from a rock called lead ore, in a process called smelting. The -radioactive lead, this lead-210 that I mentioned, behaves like ordinary -lead metal and goes along with it. - -“The radium, which has a fairly long half-life, doesn’t follow the lead -metal, but is removed with other waste products in a material called -slag. Since the longer-lived ancestor of the lead-210 is removed, the -supply of lead-210 is cut off. (Or we can say that one of the waterfalls -is shut off.) The lead-210 will then decay with its 22-year half-life.” - - [Illustration: _The radioactive series that starts with uranium is - like a series of lakes connected by waterfalls. As long as uranium, - the big one on top, has water in it, the others will be full and the - falls will keep flowing. But when the first waterfall is shut off, - the small lakes below it will run dry._] - -“I get it,” said Bill. “That means that when you take a sample of old -lead white paint, there shouldn’t be any radioactive lead-210 left.” - -“That’s right. But that would only be true if you removed all the -radium. Actually, in the smelting process it’s more usual to remove only -90 or 95% of the radium. In that case, the lead-210 would decay only -until the amount left would be equal to the small amount of radium that -wasn’t removed. In effect, this would be like shutting off only part of -the waterfall.” - -“So what do you find,” asked Harley, “if you measure the radioactivity -in a sample of lead white paint?” - -“We find that if the paint is old, compared to the 22-year half-life of -the lead, let’s say 100 years old or more, then the amount of -radioactivity from the lead-210 in the sample of paint will be equal to -the amount of radioactivity from the radium in the sample. But if the -paint is modern, let’s say only 20 years old or so, then the amount of -radioactivity from the lead-210 will be greater than the amount of -radioactivity from the radium.” - -Martin, who had been quiet through all this explanation, finally spoke -up. “Well, was it finally tried out? How did it work?” - -“Hundreds of samples were analyzed. These samples were taken from -paintings of all ages, from some over 300 years old right up to others -only a couple of years old. The old samples always showed equal amounts -of radioactivity from lead-210 and radium while the modern ones always -showed larger amounts of radioactivity from lead-210 than from radium. -That meant that scientists had a way of definitely telling if a lead -white paint was modern or not. - -“Eventually, the method was tried on a number of paintings believed to -be by Van Meegeren. Sure enough, every one of them showed that the paint -couldn’t possibly have been more than 30 or 40 years old and that Van -Meegeren probably was telling the truth when he said that he had painted -them. The paintings certainly were not genuine Vermeers from the 17th -century.” - -“Okay, Dad,” said Martin, “can we use the method on any of the paintings -we found? Are any of these paintings supposed to be old enough so that -we can use this test?” - -“Not so fast. To find that out we have to do a lot of checking first.” - -“How do we go about it?” asked Bill. - -“Let’s see now. There are nine paintings in the box you found. The first -thing we should do is take them down to a museum or gallery and let the -art experts look at them. Since we have a few weeks of vacation time -left, what do you say we take a trip down to Washington, D. C., and show -them to some experts at the National Gallery of Art?” - -Over the next few weeks quite a few things happened to the boys and -their paintings. Three of them were discarded right away because they -were immediately recognized as being copies of no value. Two were -relatively modern paintings with the signature Alfred Sisley; if -genuine, they were less than 100 years old. The remaining four appeared -to be very old paintings. Two of them seemed to correspond to paintings -that disappeared during the Second World War. Photographs and X rays -were taken and sent to the museum in Holland, which had owned the -missing pictures, so that they could make a preliminary examination. - - [Illustration: uncaptioned] - - Radioactivity of Lead-210 - - Lead-210 decaying with a half-life of 22 years. When no radium is - present there is almost none left after 6 half-lives or 132 years. - - Radioactivity of Radium-226 - - Over the same period of time, a small amount of radium decays very - little because its half-life is about 1600 years. - - Radioactivity of Radium 226 - Radioactivity of Lead-210 - - But when lead-210 decays in the presence of radium-226, the - radioactivity of the lead-210 only decreases until it is equal to - the radioactivity of the radium. - -That left two that could have been old but whose origins were unknown. A -series of simple chemical tests were begun on these and the boys watched -experts take very small samples of paint for examination under the -microscope. After several months a list of the pigments present in the -paintings was prepared. All the pigments found were typical of old -paintings and the ordinary examinations and tests couldn’t prove whether -the works were old or not. Finally, it was decided that the only way to -tell if these paintings were truly old was to apply the test that Dad -had described to the boys. - -The boys watched a painting restorer remove samples of nearly white -paint right at the edge of the paintings. He worked carefully, using a -very sharp scalpel and a stereo-binocular microscope, through which -objects appeared to be sixty times larger than they really were. The -sample of paint weighed approximately twenty-thousandths of a gram. The -boys and their father took the samples to a radiochemical laboratory -where they watched a radiochemist do the required analysis for lead-210 -and radium in the samples. - -First the chemist dissolved the paint in acetic acid. This removed the -lead white from the oil and from the small amounts of other pigments in -the paint. The solutions were then heated and stirred with a silver disc -hanging in the liquid. After several hours the disc still looked clean, -but the chemist said that a radioactive element, polonium-210, was now -plated onto the silver. Polonium-210 is a member of the uranium series -following the lead-210, and a measurement of its radioactivity would be -an accurate measurement of the radioactivity of lead-210. - -The silver discs prepared from the two samples were each placed in an -instrument called an alpha-particle spectrometer. This instrument is -extremely sensitive and can measure the very small amounts of -polonium-210 prepared from the tiny sample of paint that they started -with. - -While the instruments were making the measurements, which took a couple -of days, the chemist turned to the remaining solutions and began the -analyses for radium. - - [Illustration: _A painting being sampled under a stereo-binocular - microscope._] - - [Illustration: _Lead white weighing twenty-thousandths of a gram (20 - milligrams). This is the amount needed to measure lead-210 and - radium-226 to determine if the lead white is old._] - -In a series of chemical steps, he purified the solutions, removing the -lead and other materials so that finally he had a small amount of -solution that contained little else but the original radium and a very -small amount of barium (an element that he deliberately added and one -which is very similar to radium in its chemical properties). By adding -dilute sulfuric acid, he prepared an insoluble material, barium sulfate, -which was barely visible suspended in the solution. - - [Illustration: _Polonium plating apparatus. A heated solution of - lead white in acetic acid is stirred with silver discs for 4 to 8 - hours._] - - [Illustration: _The disc above appears clean after removal, but on - its surface it retains a minute amount of polonium which can be - measured._] - -By forcing the solution through a special thin plastic filter having -tiny holes, the particles of barium sulfate together with the radium -that had been in the solution were caught on the surface of the filter. -This was mounted on a solid disc so that it too could be placed in the -alpha-particle spectrometer for the measurement of radioactivity from -the radium. - -Two weeks later the results were ready. Dad, the boys, and one of the -experts from the museum met with the chemist to discuss them. For one of -the two paintings, the polonium-210 radioactivity was about ten times -that of the radium activity. The boys were disappointed because this -meant that the painting could not have been 300 or 400 years old as it -first appeared to be. - - [Illustration: _An alpha-particle spectrometer is used to measure - the radioactivity of the radium and polonium prepared from the lead - white._] - - [Illustration: _A plastic disc on which is cemented a filter - containing a nearly invisible deposit of barium sulfate (BaSO₄) that - “carried” the radium._] - -But in the second painting the radioactivity from the polonium-210 and -from the radium-226 were just about equal. That meant that this painting -was at least 100 years old and, from its appearance, probably more. The -boys were excited. - -“We have a really valuable painting!” said Martin. - -“Not so fast, boys,” cautioned Dad. “We don’t know who painted it and we -don’t know exactly how old it is.” - -The Gallery’s expert was happy too. He believed that the second picture -was a genuine Dutch painting from the 17th century. It was a landscape -and the artist might have been Aelbert Cuyp. - - [Illustration: _“The Maas at Dordrecht”, a genuine painting by - Aelbert Cuyp._] - -“What do we do now?” asked Harley. “How can we prove that the painting -was painted in Holland in the 17th century by Cuyp?” - -“There is a method now being developed,” said Dad, “that could give us -that kind of information.” - -“How does it work?” Martin asked. - - - - - Who Was the Artist? - - -“Do you know how criminals are caught by using fingerprints?” asked Dad. - -“Sure we do,” said Martin. “Each person has a set of fingerprints that -is different from anyone else’s.” - -Harley spoke up. “Did the artist leave his fingerprints on the -paintings?” - -“Probably not,” said Dad. “Besides, they would have been wiped off long -ago. Also, who knows what each artist’s fingerprints were like?” - -“Then what do you mean?” asked Bill. - -“What I mean is, there is another kind of ‘fingerprint’ that scientists -are just now learning to use in all kinds of identification problems. -It’s not really a fingerprint, but it’s just as distinctive as a real -fingerprint. - -“You see, in every material, no matter how pure you try to make it, -there are always other substances contained in it in very, very small -quantities, which are there only by chance. Usually the person making or -using that material doesn’t even know they are there, and the quantities -are so small they don’t do any harm. During the last several years, -scientists have developed extremely sensitive methods of analysis, which -have been applied to all kinds of problems. - -“One such method is called neutron activation analysis. In this method -these small amounts of impurities can be detected in tiny samples of -material. This is quite important because only very small samples can be -taken from a precious painting without damaging it. Normally, a -scientist or an art restorer takes samples that are no bigger than the -head of a pin.” - -“How can you do anything with a sample that small?” asked Bill. - - [Illustration: uncaptioned] - -“With neutron activation analysis you can do a great deal. To give you -an example of how sensitive this method is, think of a bathtub -containing 500 quarts of milk. Add 1 drop of an acid containing a speck -of gold dissolved in it. After you mix the acid and milk thoroughly, you -won’t be able to tell by looking at it that anything was added. But if -you take a thimble full of liquid out of the bathtub, you can easily -tell with neutron activation analysis that gold was added to the milk. - -“Scientists call low concentrations of accidental impurities ‘trace -elements’, and the amounts that are present are measured in parts per -million rather than percent. One part per million is one ten-thousandth -of a percent.” - -Bill spoke up again. “So how does that make a fingerprint, Dad?” - -“It works this way. Suppose an artist used lead white in several -paintings. Now if the lead white were absolutely pure it would contain -only lead, carbon, oxygen, and hydrogen. But the lead white the artist -used would also contain very small quantities of other elements, these -trace elements that I spoke of. In that particular batch of lead white, -certain trace elements will be present in a certain quantity. The kind -and amount of the trace elements will be present in that exact pattern -only in that batch of lead white. - -“Now suppose you analyze the lead white from several paintings that you -know were painted by that particular artist, and you find that there is -silver, mercury, antimony, tin, and barium in every one of the samples. -Also, each of these elements is always present in a certain -concentration. Suppose also, that you have a painting which looks like -it was painted by that particular artist but you’re not quite sure. - -“Well, if you take a sample of lead white from that unknown painting and -you find that the pattern of impurities is the same as in the paintings -you knew were genuine, then the ‘fingerprints’ match. The chances of -duplicating impurities of this kind by pure accident are extremely -small, just about as small as the chances of finding two people with the -same fingerprints. That’s why we call this a ‘fingerprint method’.” - -“That sounds like a good idea,” said Harley. “Who thought it up?” - - x = one part per million (ppm) - A known Rembrandt. - - x - x - x x x - x x x x - x x x x - x x x x x - x x x x x - x x x x x x - silver chromium zinc manganese iron cobalt - - Unknown painting A - - x - x - x x - x x - x x x - x x x x - x x x x - x x x x x - x x x x x x - silver chromium zinc manganese iron cobalt - - Unknown painting B - - x - x - x x x - x x x x - x x x x - x x x x x - x x x x x - x x x x x x - silver chromium zinc manganese iron cobalt - - Known forgery - - x - x - x x - x x - x x x - x x x x - x x x x - x x x x x - x x x x x x - silver chromium zinc manganese iron cobalt - - _Match the patterns of these lead white “fingerprints”. Unknown - painting A is_ not _a Rembrandt; it_ is _by the same forger who - painted the known forgery at the bottom. Unknown painting B is - either by Rembrandt, one of his fellow citizens, or one of his - students using the same paint._ - -“It was thought of many times by many people. But, it’s never been used -for identifying paintings. In 1964 in the Netherlands, two scientists, -named Houtman and Turkstra, analyzed about 40 different samples of lead -white, 20 of which came from Dutch and Flemish paintings. The rest were -samples of lead white not taken from paintings but obtained directly -from the manufacturers. They analyzed these samples for different -elements. These included silver, mercury, chromium, manganese, tin, -antimony, and a couple of others. - -“They found that the concentrations of these elements in the lead white -from all the old Dutch and Flemish paintings were very similar. And the -trace element concentrations were quite different in the modern lead -white samples analyzed in the same way. At the time, they presumed that -it was because the lead white in the paintings was manufactured so long -ago. They may have been right to a certain extent. - -“For example, they found that in all the old paintings there were from -10 to 30 parts per million of silver in the lead white, while in the -modern samples of this pigment there were generally less than 10 parts -per million of silver. All of them had been painted before the 19th -century, and all the samples of pure lead white were manufactured during -the latter part of the 19th century or during the 20th century. They -believed that the reason the silver concentration was lower in the more -modern material was because during the 19th century, lead refiners were -doing a better job of removing all the valuable silver from lead. - - [Illustration: _Silver concentrations in lead white. The - concentrations generally decreased after the middle 1800s. Notice - also how the concentrations were very similar for all the older - paintings (before 1700) which were Dutch or Flemish._] - -“However, in 1967 in Germany, two men, named Lux and Braunstein, -discovered that in some old paintings produced in Italy, lead white also -contained low quantities of silver just like modern material. They -believed that the higher concentrations of silver in lead white were -typical of Dutch and Flemish painters while the lower concentrations -were typical of Italian paintings of about the same age. - -“The whole case is still unsettled because not enough measurements have -been made to show how reliable this method can be. That is, no one knows -if samples of paint from several paintings by one artist would all have -the same pattern of impurities in the same pigment. It may be that of -the many pigments present in an artist’s paintings only a few will be -suitable for use in this ‘fingerprinting’ method.” - - [Illustration: _Quartz vials (right) containing samples are sealed - in the aluminum can on the left. They are then bombarded with - neutrons in a reactor like the one in the picture below._] - -“It sounds complicated,” said Bill. - -“It is, and it’s going to take years of work before the method is -proven, if it is at all. It may turn out that you can’t tell one artist -from another, but only groups of artists like 17th century Dutch -painters or 19th century English painters.” - -“Tell us something about neutron activation analysis,” said Martin. “How -do you measure such small amounts of impurities?” - -“The best way to tell you how this works is to show you. How would you -boys like to visit a laboratory where neutron activation analysis is -being done?” - -“Do you have to ask?” said Harley. “Of course we would!” - -A few weeks later it was all arranged. At a laboratory close by a -nuclear reactor, the boys watched a radiochemist place a few specks of -material inside small quartz tubes that were then sealed. The tubes were -put in an aluminum can and placed in the nuclear reactor. The can was -fastened on the end of a long pole that was then submerged in a deep -pool of water. At the bottom of the pool the boys could see a bright -blue glow. - - [Illustration: _This type of nuclear reactor is used for neutron - activation analysis._] - -“So that’s what a nuclear reactor looks like!” said Bill. - -“Yes,” said Dad. “Where you see the blue glow you can also see rows of -fuel elements. Each one contains slugs of uranium encased in aluminum. -This is one of a number of different types of reactors. But every -nuclear reactor is arranged so that the uranium atoms divide (or -fission) many, many times each second. - -“When this happens, heat is produced that is carried away by the water, -and also many, many free neutrons are produced. Those samples, placed -down next to the reactor in the bottom of the pool are being bombarded -by the neutrons, and some of the elements in the samples absorb the -neutrons and become radioactive.” - -After a while the samples were removed and carried back to the -laboratory in a lead box. A short while later, the radiochemist opened -the aluminum can, broke open the quartz capsules, and removed the -samples for analysis. The boys watched the chemist mount each sample on -a card and take it to a room where there was equipment for measuring -radioactivity. - - [Illustration: _Gamma-ray spectrometer. The sample to be measured is - placed on a stand over a gamma-ray detector. The pulse-height - analyzer is a device that sorts electrical impulses from the - detector according to the energy of the gamma rays causing the - impulses. The screen displays the gamma-ray spectrum and the - electric typewriter automatically types out the data collected when - the measurement is complete._] - -One by one the samples were placed inside a shield consisting of a big -pile of lead bricks. When the heavy door was opened, the boys could see -a metal can inside the shield, which housed a detector (called a -lithium-drifted germanium detector) that measured the gamma rays emitted -by the sample. As each sample was placed near the detector the chemist -turned on a gamma-ray spectrometer to which the detector was connected. - - A tiny sample of lead white {sample} is sealed in a quartz vial - {vial} which is bombarded with neutrons in a reactor. - - [Illustration: uncaptioned] - - Many of the atoms become radioactive, emitting gamma rays. - - [Illustration: uncaptioned] - - The sample is placed in a gamma-ray spectrometer and the gamma rays - are separated according to their energy. - - [Illustration: uncaptioned] - - Gamma-ray spectrum - Copper - Zinc - Antimony - Lead - Silver - Height - Antimony - - The location (energy) of each peak indicates what is present and the - height indicates how much! - - [Illustration: _A gamma-ray spectrum as it appears on the screen of - a pulse-height analyzer. The gamma-ray peaks are marked with the - name of the element whose radioactive isotope emits the gamma ray; - two for cobalt and zinc and one for cesium._] - -There, on what looked like a small television screen, flashes of light -appeared that gradually formed a curve with many peaks and valleys. -After a few minutes the spectrometer was stopped and an electric -typewriter automatically typed out rows and columns of numbers. - -The chemist explained, “This curve, which you see on the screen, is a -gamma-ray spectrum and tells us what elements are in the sample. The -typed-out data give us an accurate measure of the shape of the curve on -the screen. By measuring the gamma-rays’ energies we know what elements -in the sample were made radioactive. The height of each gamma-ray peak -tells us how much of that element is present in the sample. - -“That gives us the information we need to calculate the concentrations -of the small quantities of materials in our samples. We can do this -because at the same time I irradiated a set of standards. Standards are -materials that are just like the samples except that they contain known -amounts of the impurities I am trying to measure.” - -As the boys were leaving the laboratory, the chemist apologized for not -having enough time to explain the activation analysis procedure more -thoroughly, but he did give the boys a list of books to read on the -subject of radioactivity and radioisotopes.[2] They thanked him for his -help. - -During the ride home, they discussed the paintings that were still -unproven. - -“It’s too bad that the method of activation analysis fingerprinting -hasn’t been fully developed yet,” said Dad. - -“Yes,” said Bill. “Then we could prove whether or not that last old -painting was really by Aelbert Cuyp as the expert from the gallery -believed. But what about those paintings that we found in the box that -were not so old?” - -“Well,” said Dad, “if the activation analysis method were workable, we -might be able to prove if they were painted by Alfred Sisley. Meanwhile, -until the method is really developed we don’t know if we can do it that -way or not.” - -“So what do we do now?” asked Martin. - -“We’ll have to wait until scientists can thoroughly investigate this -method and several others that they’re working on.” - -“Other methods!” exclaimed Bill. “What other methods?” - - [Illustration: _“The Banks of the Oise”, a genuine painting by - Alfred Sisley._] - - - - - Other New Tools for Art Authentication - - -“There are several new tools that scientists are working on now,” said -Dad. “These involve methods that have been developed by scientists for -other purposes, but are now being explored for use in authenticating -works of art. - -“For example, in Los Angeles, the county museum purchased an instrument -known as a Spark Source Mass Spectrometer. Like activation analysis, -this instrument will also measure small traces of impurities, but they -have just set that up and it will take them years to explore the use of -it for the type of problem we have been discussing. - -“X-ray diffraction is another method that has been around for quite -awhile but hasn’t been used much for art identification until recently. -With X-ray diffraction, samples of pigments can be identified by the -pattern formed when X rays are bent by passing through the sample of -pigment.” - -“How’s that?” asked Harley. - -“There are 3 or 4 different compounds with about the same chemical -composition as lead white. Chemically, they are almost impossible to -distinguish. But with X-ray diffraction, a chemist can easily tell them -apart. The hope is that the type of lead white will indicate how it was -manufactured. Until the middle of the 19th century, lead white was -produced mainly by packing strips of lead in clay pots with a little -vinegar in the bottom. The clay pots were stacked in a large building -with layers of decaying organic matter on the floor. The building was -sealed for several weeks during which time the lead corroded in the -fumes and became covered with a white substance. The white substance, -lead white, was scraped off, ground, and washed to make the pigment. - -“But, in the 19th century, when people began to learn more about -chemistry, they looked for faster ways of making lead white and some of -these methods produced a lead white of somewhat different composition. -By using X-ray diffraction, chemists now hope that they can tell how the -lead white was manufactured. This may provide another means of dating -the lead white in a painting.” - -“Are there any other methods?” asked Harley. - - [Illustration: _The stack process for making lead white. Rows of - clay pots containing lead and vinegar are packed to the ceiling of - the building, and fermenting tanbark on the floor produces carbon - dioxide and heat. The fumes of vinegar and the carbon dioxide - corrode the lead in 2 to 4 months, and the corrosion is lead - white._] - -“Yes, isotope mass spectrometry is one. All lead consists of 4 different -isotopes or atoms of different weights. Three of these 4 are the end -products of a radioactive decay chain. Depending upon the history of the -rock formation in which the lead ore occurred, the relative amounts of -the lead isotopes vary in a special way. In other words, if we know the -different amounts of lead isotopes in the world’s lead ore deposits, and -we have a sample of lead white from a painting, we can tell from which -deposit the lead, which formed the lead white, came. If, for example, we -find that the isotope pattern in a sample from a painting is the same as -in lead ore from Australia, then the painting can’t be very old because -lead white wasn’t produced from lead mined in Australia until about 100 -years ago.” - - [Illustration: _X-ray diffraction patterns from three different lead - compounds that might occur in lead white. The middle one is the - ideal lead white produced for over 2000 years. While some of the - bottom compound may be found mixed with it, the compound shown at - the top is only a 20th-century invention._] - - 4PbCO₃ · 2PB(OH)₂ · PbO - 2PbCO₃ · PB(OH)₂ - PbCO₃ - -“How do you measure lead isotopes?” asked Harley. - -“With an instrument called a mass spectrometer. This instrument is -capable of separating the lead isotopes. First, the atoms of lead in the -sample are electrically charged and ‘fired’ in a beam down the length of -a tube between the poles of a strong magnet. There, the charged atoms -(or ions) in the beam are deflected by different amounts according to -how heavy they are. Thus the different isotopes are separated. This -method is also still being studied and, although it shows great promise, -it will be some time before it can solve problems of art identification. -Also the study of the natural variation in isotopes of other elements, -such as sulfur, is useful for identification of other pigments as well. - - [Illustration: _Diagram of a simple mass spectrometer. The ionized - atoms of lead travel in a beam at the same speed. The heavier atoms - bend less than the lighter ones when the beam passes the magnet. - Thus two beams emerge instead of one. Actually there are four - isotopes of lead so there will be four beams._] - - [Illustration: _“Agostina”, a genuine painting by Jean Baptiste - Camille Corot._] - -“Another new method that shows great promise has been developed, but -this one is not applicable to the paintings that you boys found in the -box.” - -“Why not?” asked Bill. - -“Since the Second World War, the art forgery business has been growing -rapidly. For example, it has been said that of the 2000 pictures that -Corot, a 19th century Frenchman, is known to have painted, more than -5000 of them are in the United States. This may be only a humorous -exaggeration, but a large number of forgeries have been produced in the -last several years. These are usually supposed to be paintings that are -less than 100 years old. Present-day forgers like to forge paintings -that aren’t very old because it’s easier to get away with. Now this new -method, which will detect such recent forgeries, is based upon the -presence of carbon-14, a radioactive isotope of carbon, in our -atmosphere and in all things that grow on our planet. - -“Ordinarily, carbon-14 is produced only by cosmic rays, and its -concentrations in the atmosphere and in growing things would remain at a -constant level. But since the middle of the 1950s the testing of nuclear -weapons has increased the amount of radioactive carbon in our atmosphere -by quite a bit. Many artist’s materials, such as linseed oil, canvas, -paper, and so on, come from plants or animals, and so will contain the -same concentrations of carbon-14 as the atmosphere up to the time that -the plant or animal dies. - -“Therefore, linseed oil (from the flax plant), for example, produced -during the last few years will have a much greater concentration of -carbon-14 in it than linseed oil produced more than 20 years ago. -Scientists at Carnegie-Mellon University have shown that this method -will work. It is only a matter of making the measurements on the small -samples available from presumably valuable paintings.” - - [Illustration: _The changing concentrations of carbon-14 in our - atmosphere. High levels of carbon-14 in linseed oil and other - painting materials will indicate that a work of art is only a few - years old._] - - Carbon-14 radioactivity - Older materials contain less as the carbon-14 decays away. - In this period, decrease is due to the burning of large quantities - of coal and oil as industry grew. This diluted the newly - formed carbon-14. - Increases due to testing of atomic weapons in the atmosphere. - Carbon-14 produced by cosmic rays only - Neutron → Nitrogen → Carbon-14 + proton - Carried down by rain in carbon dioxide - -“There are also a number of other methods being studied including the -use of Messbauer Effect Spectroscopy to study pigments that contain -iron, thermoluminescent dating of pottery and terra-cotta statuary, -X-ray fluorescence analysis as a general tool, and neutron -autoradiography as a means of studying the technique of artists. You can -read all about them if you wish.”[3] - -“It sounds like forgers are going to have a tough time in the future,” -said Harley. - -“That’s right. It may even turn out that producing forgeries to pass all -these new tests will be so difficult and expensive that forgers will -stop trying.” - - - - - One Mystery Solved - - -A year later an important letter arrived at the boys’ house. Dad opened -it, read it quickly, and said, “Good news, boys! This letter is from the -Dutch government. Remember those two paintings that we thought might -have been stolen from a Dutch museum?” - -“Yes,” said Bill. - -“Well, it seems that after a year of studying them, the Dutch have -decided that they really are the paintings that were stolen.” - -“That is good news,” said Harley. “At least we know that two of the -paintings we found are genuine.” - -“What are they going to do with them?” asked Martin. - -“Of course, they have to go back to their original owners. But this -letter says that the Dutch government wants us to come to Holland as -their guests as a reward for finding those paintings.” - - [Illustration: _These two paintings “The Lacemaker” and “The Smiling - Girl” were thought to have been by Vermeer. A series of tests, - including some of those described in this booklet, showed that the - paintings are fairly old. However, some of the materials used are - not typical of Vermeer, and the pictures are now thought to have - been painted by a follower of the artist._] - -“That’s great!” said Bill. “Looks like we’re getting something out of -finding that box after all.” - -“Yes,” said Dad. “And don’t forget the other unidentified paintings may -also be genuine. We’ve proved that one is a fake, the experts believe -that three of the others are copies, and then there are the two that -might be Sisleys and are only waiting for a method to prove it. And we -have one more that science managed to prove was really old. I’m sure -that in a few years methods will be developed to tell us exactly who -painted it. - -“And now let’s make arrangements for our trip to Holland.” - - - - - Reading List - - -_About Atomic Power for People_, Edward and Ruth S. Radlauer, Childrens - Press, Chicago, Illinois 60607, 1960, 47 pp., $2.50. Grades 5-9. - -_All About the Atom_, Ira M. Freeman, Random House, Inc., New York - 10022, 1955, 146 pp., $2.50. Grades 4-6. - -_Atoms at Your Service_, Henry A. Dunlap and Hans N. Tuch, Harper and - Row, Publishers, New York 10016, 1957, 167 pp., $4.00. Grades 7-9. - -_Carbon-14 and Other Science Methods that Date the Past_, Lynn and Gray - Poole, McGraw-Hill Book Company, New York 10036, 1961, 160 pp., - $3.95. Grades 9-12. - -_Experiments with Atomics_ (revised edition), Nelson F. Beeler and - Franklyn M. Branley, Crowell Collier and Macmillan, Inc., New York - 10022, 1965, 160 pp., $3.50. Grades 5-8. - -_The Fabulous Isotopes: What They Are and What They Do_, Robin McKown, - Holiday House, Inc., New York 10022, 1962, 189 pp., $4.50. Grades - 7-10. - -_Inside the Atom_ (revised edition), Isaac Asimov, Abelard-Schuman, - Ltd., New York 10019, 1966, 197 pp., $4.00. Grades 7-10. - -_Introducing the Atom_, Roslyn Leeds, Harper and Row, Publishers, New - York 10016, 1967, 224 pp., $3.95. Grades 7-9. - -_Our Friend the Atom_, Heinz Haber, Golden Press, Inc., New York 10022, - 1957, 165 pp., $4.95 (out of print but available through - libraries); $0.35 (paperback) from Dell Publishing Company, Inc., - New York 10017. Grades 7-9. - -_Radioisotopes_, John H. Woodburn, J. B. Lippincott Company, - Philadelphia, Pennsylvania 19105, 1962, 128 pp., $3.50. Grades - 7-10. - -_The Story of Atomic Energy_, Laura Fermi, Random House, Inc., New York - 10022, 1961, 184 pp., $1.95. Grades 7-11. - -_The Useful Atom_, William R. Anderson and Vernon Pizer, The World - Publishing Company, New York 10022, 1966, 185 pp., $5.75. Grades - 7-12. - -_Working with Atoms_, Otto R. Frisch, Basic Books, Inc., Publishers, New - York 10016, 1965, 96 pp., $3.50. Grades 9-12. - - -Footnotes - - -[1]It is called this because 210 is the total number of protons and - neutrons in its nucleus. - -[2]See the reading list on page 44. - -[3]See _Secrets of the Past: Nuclear Science and Archaeology_, which is - listed on the inside back cover of this booklet. - - -PHOTO CREDITS - -Cover courtesy Groninger Museum voor stad en Lande - - Page - - 5 Yale Joel, _Life_ magazine, copyright © Time, Inc. - 6 Her Majesty the Queen, copyright © reserved - 7 & 8 Ullstein Bilderdienst - 10 Rijksmuseum, Amsterdam - 23 National Gallery of Art, Washington, D. C., Andrew Mellon - Collection - 35 & 40 National Gallery of Art, Washington, D. C., Chester Dale - Collection - 43 National Gallery of Art, Washington, D. C., Andrew Mellon - Collection - - ★ U.S. GOVERNMENT PRINTING OFFICE: 1974—747-556/15 - - -The U. S. Atomic Energy Commission publishes this series of information -booklets for the general public. The booklets are listed below by -subject category. - -If you would like to have copies of these booklets, please write to the -following address for a booklet price list: - - USAEC—Technical Information Center - P. O. Box 62 - Oak Ridge, Tennessee 37830 - -School and public libraries may obtain a complete set of the booklets -without charge. 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} -dl.catalog dt { margin-top:1em; } -.author { text-align:right; margin-top:0em; margin-bottom:0em; display:block; } - -dl.biblio dt { margin-top:.6em; margin-left:2em; text-indent:-2em; text-align:justify; clear:both; } -dl.biblio dt div { display:block; float:left; margin-left:-6em; width:6em; clear:both; } -dl.biblio dt.center { margin-left:0em; text-align:center; text-indent:0; } -dl.biblio dd { margin-top:.3em; margin-left:3em; text-align:justify; font-size:90%; } -p.biblio { margin-left:2em; text-indent:-2em; } -.clear { clear:both; } -p.book { margin-left:2em; text-indent:-2em; } -p.review { margin-left:2em; text-indent:-2em; font-size:80%; } -p.pcap { margin-left:0em; text-indent:0; text-align:justify; margin-top:0; - font-size:90%; } -p.pcapc { margin-left:4em; text-indent:0em; font-size:80%; text-align:justify; font-family:sans-serif; } -p.pcap b { font-family:sans-serif; } -dl.pcap { font-family:sans-serif; font-size:80%; margin-left:2em; } -span.attr { font-size:80%; font-family:sans-serif; } -span.pn { display:inline-block; width:4.7em; text-align:left; margin-left:0; text-indent:0; } -</style> -</head> -<body> - -<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of The Mysterious Box, by Bernard Keisch</div> - -<div style='display:block; margin:1em 0'> -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online -at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Title: The Mysterious Box</p> -<p style='display:block; margin-top:0; margin-bottom:1em; margin-left:2em; text-indent:0;'>Nuclear Science and Art</p> - -<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Bernard Keisch</div> - -<div style='display:block; margin:1em 0'>Release Date: August 18, 2021 [eBook #66082]</div> - -<div style='display:block; margin:1em 0'>Language: English</div> - -<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div> - -<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Stephen Hutcheson and the Online Distributed Proofreading Team at https://www.pgdp.net</div> - -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE MYSTERIOUS BOX ***</div> -<div id="cover" class="img"> -<img id="coverpage" src="images/cover.jpg" alt="The Mysterious Box: Nuclear Science and Art" width="1000" height="1551" /> -</div> -<div class="box"> -<h1>THE MYSTERIOUS BOX: -<br />Nuclear Science and Art</h1> -<p class="center"><span class="ss"><span class="rubric">by -<br />Bernard Keisch</span></span></p> -</div> -<h2 id="toc" class="center">Contents</h2> -<dl class="toc"> -<dt><a href="#c1">The Mysterious Box</a> 2</dt> -<dt><a href="#c2">How Old Is a Painting?</a> 11</dt> -<dt><a href="#c3">Who Was the Artist?</a> 24</dt> -<dt><a href="#c4">Other New Tools for Art Authentication</a> 36</dt> -<dt><a href="#c5">One Mystery Solved</a> 42</dt> -<dt><a href="#c6">Reading List</a> 44</dt> -</dl> -<p class="center smaller">United States Atomic Energy Commission -<br />Office of Information Services -<br />Library of Congress Catalog Card Number: 70-606040 -<br />1970; 1974 (rev.)</p> -<div class="pb" id="Page_i">i</div> -<h3>The Author</h3> -<div class="img"> -<img src="images/p01.jpg" id="ncfig1" alt="Bernard Keisch" width="652" height="800" /> -</div> -<p>Dr. Bernard Keisch received his B.S. degree from Rensselaer -Polytechnic Institute and his Ph.D. from Washington University. -He is a Senior Fellow with the Division of Sponsored -Research of Carnegie-Mellon University in Pittsburgh. He is -presently engaged in a project that deals with the applications -of nuclear technology to art identification. This is jointly -sponsored by the U. S. Atomic Energy Commission and the -National Gallery of Art. Previously he was a nuclear research -chemist with the Phillips Petroleum Company and senior -scientist at the Nuclear Science and Engineering Corporation. -He has contributed articles on art authentication to a number -of journals. For the AEC, in addition to this booklet, he has -written <i>The Atomic Fingerprint: Neutron Activation Analysis</i>, -<i>Secrets of the Past: Nuclear Energy Applications in Art -and Archaeology</i>, and <i>Lost Worlds: Nuclear Science and -Archaeology</i>.</p> -<div class="pb" id="Page_ii">ii</div> -<div class="box"> -<p>Nuclear energy is playing a vital role in -the life of every man, woman, and child in the -United States today. In the years ahead it will -affect increasingly all the peoples of the earth. -It is essential that all Americans gain an -understanding of this vital force if they are to -discharge thoughtfully their responsibilities as -citizens and if they are to realize fully the -myriad benefits that nuclear energy offers -them.</p> -<p>The United States Atomic Energy Commission -provides this booklet to help you -achieve such understanding.</p> -</div> -<div class="box"> -<h3><a href="#cover">The Cover</a></h3> -<p>This painting, originally believed to be the -work of the Dutch artist Frans Hals -(1580-1666), is a fake. Measurements of the -naturally radioactive isotopes, polonium-210 -and radium-226, in lead white from the paint -proved that it was no more than 50 years old.</p> -</div> -<div class="pb" id="Page_1">1</div> -<div class="img" id="fig1"> -<img src="images/p02.jpg" alt="" width="758" height="1199" /> -<p class="pcap"><i>A Van Meegeren forgery of a Vermeer.</i></p> -</div> -<div class="pb" id="Page_2">2</div> -<h2 id="c1"><span class="small">The Mysterious Box</span></h2> -<p>The New Jersey sun was high overhead -and the day was hot. The three boys walking -along a deserted stretch of beach didn’t mind -because they were barefoot and in their -swimsuits. Occasionally they would dash in -and out of the surf to cool off.</p> -<p>Suddenly Martin let out a yell as his toe -hit something hard hidden in the sand at the -water’s edge. A moment later Bill and Harley -were helping Martin dig out a large wooden -case. It was heavy, well built, tightly sealed, -and had foreign words written on it.</p> -<p>“Maybe it’s a pirate treasure chest,” said -Martin, who was almost eight and had just -read <i>Treasure Island</i> for the first time the -week before.</p> -<p>“You’re crazy,” said Harley, who, nearly -ten, was much older and wiser.</p> -<p>Bill, going on twelve, thought aloud, “It -must be something worthwhile; maybe we can -sell it and buy those model rockets we -wanted.”</p> -<p>The three boys soon found that they -couldn’t open the box and that it was too -heavy to drag along the sand easily.</p> -<p>“Martin,” said Bill, “get Dad while Harley -and I stand guard.”</p> -<p>Two hours later the box was at their -house and everyone in the family was trying -to read what was written on it. About all that -was readable was a large “U” followed -by what appeared to be two numbers. Some -<span class="pb" id="Page_3">3</span> -of the other marks looked like old German -script and there was a date, 1945.</p> -<p>“You know,” said Bill, “I bet that came -from a World War II German submarine that -our Coast Guard or Navy sank.”</p> -<p>“Let’s open it up!” said Harley as Martin -ran to get the screwdrivers.</p> -<p>Inside they found a thoroughly waxed -carton that they had to cut open. Everyone -held their breath as their father lifted the top.</p> -<p>“Nothing but a bunch of pictures,” said -Martin who was still hoping for pirate treasure.</p> -<p>“Paintings can be worth a lot of money,” -said Dad, “thousands or even millions of -dollars.”</p> -<p>“Well then we’re rich!” yelled Harley and -Bill together.</p> -<p>“Not so fast,” said Dad. “First of all, we -don’t know if the paintings are really valuable. -Also, it looks like these might be part of -the art treasures that the Nazis stole from the -countries they conquered in World War II. -Maybe someone was trying to get them by -submarine to a neutral country, like Argentina, -just before the end of the war, and the -sub was sunk. If they are real and stolen, -they’ll have to go back to their rightful -owners. But cheer up, maybe there’s a reward.”</p> -<p>“How do we collect it?” asked Bill. “If -the Nazis grabbed them, aren’t they real for -sure?”</p> -<p>“Not necessarily,” Dad continued. “The -Nazis were fooled sometimes by people who -sold them fakes. There was one painting that -<span class="pb" id="Page_4">4</span> -Hitler’s sidekick, Göring, bought that was -supposed to be a 17th century painting by -Vermeer, a Dutch painter. Because Vermeer’s -work is so valuable, it’s usually impossible to -buy one for any amount of money.</p> -<p>“Vermeer is regarded as a national hero -by the Dutch. The matter was investigated -and the painting traced to Han Van -Meegeren, a modern Dutch painter who had -only a fair talent. When Van Meegeren realized -he might be charged with treason by the -Dutch for selling a Vermeer to the Nazis, he -confessed that he had painted it himself. He -also confessed that he had painted other -forgeries that fooled some of the experts and -were sold for a lot of money.</p> -<p>“Many people, however, thought Van -Meegeren was only lying to save himself from -the charge of treason, and the whole thing -had to be decided by a committee of scientific -art experts appointed by a court of law. -Using the methods that were then available, -the experts showed that Van Meegeren had -done a remarkable job of forgery and they -were convinced that he had been telling the -truth about painting those pictures.</p> -<p>“At the time, the important ways the -experts used to examine a painting included -studying the work with X rays, which could -show another painting underneath, analyzing -the pigments (or coloring materials) used in -the paint, and examining the painting for -certain signs of old age.</p> -<div class="pb" id="Page_5">5</div> -<div class="img" id="fig2"> -<img src="images/p03.jpg" alt="" width="621" height="999" /> -<p class="pcap"><i>Han Van Meegeren listens to the evidence at his trial -in Amsterdam. In the background is “The Blessing of -Jacob”, which was sold in 1942 as the work of -Vermeer.</i></p> -</div> -<div class="pb" id="Page_6">6</div> -<div class="img" id="fig3"> -<img src="images/p04.jpg" alt="" width="800" height="914" /> -<p class="pcap"><i>An authentic Pieter de Hooch work, “The Card Players”, painted in the -17th century.</i></p> -</div> -<div class="pb" id="Page_7">7</div> -<div class="img" id="fig4"> -<img src="images/p04a.jpg" alt="" width="800" height="922" /> -<p class="pcap"><i>A forgery of a Pieter de Hooch picture painted in the 20th century by -Han Van Meegeren.</i></p> -</div> -<div class="pb" id="Page_8">8</div> -<div class="img" id="fig5"> -<img src="images/p05.jpg" alt="" width="455" height="600" /> -<p class="pcap"><i>“Head of Christ” by Van -Meegeren.</i></p> -</div> -<p>“Van Meegeren was well acquainted with -these methods. He scraped the paint from old -paintings that weren’t worth much just to get -the canvas and tried to use pigments that -Vermeer would have used. He knew that old -paint was very, very hard and impossible to -dissolve; so he cleverly mixed a chemical -(phenolformaldehyde) into his paint, and this -hardened into Bakelite when he heated the -finished painting in an oven.</p> -<p>“For some of the paintings, Van Meegeren -became careless and the experts did find -traces of a modern pigment (cobalt blue) in -the paint. They also found the Bakelite. For -one or more paintings, Van Meegeren did so -well that, in spite of all this evidence, a few -people still weren’t convinced that these -paintings were painted by Van Meegeren and -not by Vermeer.”</p> -<p>Bill, who by this time was bursting with -questions, interrupted, “You mean they still -aren’t sure about some of those paintings -after 25 years? Aren’t there better ways of -telling whether a painting is genuine or not? -You’re a scientist. Can’t scientists like you do -something about it now?”</p> -<p>“Yes, recently a method was developed to -settle just such a question. It’s based on -measurements of natural radioactivity in one -pigment that all artists used hundreds of years -ago. And the method was applied to some of -the Van Meegeren paintings including the best -one of them all.”</p> -<p>“How did it come out?” asked Martin.</p> -<div class="pb" id="Page_9">9</div> -<div class="img" id="fig6"> -<img src="images/p05b.jpg" alt="" width="622" height="800" /> -<p class="pcap"><i>An X ray of part of the Van Meegeren forgery, “Christ and His -Disciples at Emmaus”. In the -white circle are traces of paint from the original painting that Van -Meegeren scraped off to obtain the old canvas. When the painting was -believed to be a genuine Vermeer, it was sold for about $300,000.</i></p> -</div> -<div class="img" id="fig7"> -<img src="images/p05d.jpg" alt="" width="800" height="706" /> -<p class="pcap">The complete painting.</p> -</div> -<div class="pb" id="Page_10">10</div> -<div class="img" id="fig8"> -<img src="images/p06.jpg" alt="" width="800" height="930" /> -<p class="pcap"><i>A Van Meegeren forgery of a Vermeer.</i></p> -</div> -<p>“How does it work?” asked Harley.</p> -<p>“You mean paintings are radioactive?” -exclaimed Bill.</p> -<p>“Can we do it to the paintings we -found?” asked all three together.</p> -<div class="pb" id="Page_11">11</div> -<h2 id="c2"><span class="small">How Old Is a Painting?</span></h2> -<p>“One question at a time. I’ll tell you how -the method works and what it does if you’re -really interested.”</p> -<p>“We’re interested! We’re interested!” -chorused the boys.</p> -<p>“In the first place, this method works -only in certain cases of suspected forgery. -Over the last 50 or 100 years, a number of -paintings have turned up that seemed, even -to the best art experts, to be several hundred -years old. Some of these were genuine, and -some were painted by forgers who could not -resist the high prices paid for works of art. The -National Gallery of Art, in Washington, D. C., -thinking that there might be a way of -detecting these forgeries, gave its support to a -group of scientists who developed a method -for this purpose.</p> -<p>“To understand how the method works, -you need to know a little about how radioactive -atoms disintegrate to form atoms of -other elements. In this case we are interested -in the natural radioactivity that occurs in -certain rocks. As a matter of fact, in almost -all rocks in the earth’s crust there is a certain -small quantity of uranium.”</p> -<p>“I thought uranium was rare,” interrupted -Bill.</p> -<p>“It is, but we’re talking about such small -quantities that its difficult for scientists using -the most sensitive equipment to detect it. The -uranium in the rock decays to another radioactive -element and that one decays to -another, and another, and another, and so -<span class="pb" id="Page_12">12</span> -forth, in a series of elements that results in -lead, which is not radioactive. In this series -are two radioactive elements, radium and a -radioactive isotope of lead, that help us to -date paintings. To understand this, we must -first understand how radioactive elements -decay.</p> -<p>“All radioactive elements have what is -known as a ‘half-life’; that is, in a certain -period of time, half of the element disintegrates -to another form. In another equal -period of time, half of what is left -disintegrates, and then half again, and so on. -In the case of the uranium, which starts the -series I am describing, the half-life is over -4,000,000,000 years. Because of its long -half-life there is plenty of uranium around -and will be for a long, long time. On the other -hand, radium, which I mentioned a moment -ago, has a half-life of only 1600 years. In -1600 years, half of it would be gone, and in -another 1600 years half of that would be -gone, and so on.</p> -<p>“The radioactive lead that we’re interested -in has a half-life of only 22 years. This -means that if you start with a small quantity -of this radioactive isotope of lead, which is -called lead-210,<a class="fn" id="fr_1" href="#fn_1">[1]</a> then in only a few hundred -years it would have disappeared. However, in -rock, where there is uranium, the uranium -keeps feeding the elements following it in the -series, so that as fast as they decay they are -reproduced by the element before them.”</p> -<div class="pb" id="Page_13">13</div> -<div class="img" id="fig9"> -<img src="images/p07.jpg" alt="" width="1200" height="755" /> -<p class="pcap"><i>The Uranium Series. In this simplified diagram, the -double vertical arrows represent alpha radioactivity -and the single slanted arrows represent -beta radioactivity. The times shown on the arrows -are the half-lives for each step.</i></p> -</div> -<dl class="undent pcap"><dt>Uranium-238</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">4½ billion years</span></dd> -<dt>Thorium-234</dt> -<dd class="t">↓<sup>β</sup><span class="hst">24 days</span></dd> -<dt>Protoactimum-234</dt> -<dd class="t">↓<sup>β</sup><span class="hst">1⅕ minutes</span></dd> -<dt>Uranium-234</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">¼ million years</span></dd> -<dt>Thorium-230</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">80 thousand years</span></dd> -<dt>Radium-226</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">1600 years</span></dd> -<dt>Radon-222</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">3⅘ days</span></dd> -<dt>Polonium-218</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">3 minutes</span></dd> -<dt>Lead-214</dt> -<dd class="t">↓<sup>β</sup><span class="hst">27 minutes</span></dd> -<dt>Bismuth-214</dt> -<dd class="t">↓<sup>β</sup><span class="hst">20 minutes</span></dd> -<dt>Polonium-214</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">less than one second</span></dd> -<dt>Lead-210</dt> -<dd class="t">↓<sup>β</sup><span class="hst">22 years</span></dd> -<dt>Bismuth-210</dt> -<dd class="t">↓<sup>β</sup><span class="hst">5 days</span></dd> -<dt>Polonium-210</dt> -<dd class="t">⇓<sup>α</sup><span class="hst">138 days</span></dd> -<dt>Lead-206</dt> -<dd class="t">(Not Radioactive)</dd></dl> -<div class="pb" id="Page_14">14</div> -<p>“I don’t quite understand how that -works,” said Harley. “What do you mean ‘it -keeps feeding it’?”</p> -<p>“Well, think of a series of lakes connected -by waterfalls. At the top, the highest lake has -an enormous supply of water. Following the -waterfall coming out of the lake you find a -smaller lake and then maybe a medium-sized -lake, and after another waterfall, a smaller -lake, then a tiny lake, and so on.</p> -<p>“As long as that big lake on top is full or -nearly full, all the other lakes, whether they -are small or medium-sized, will still be getting -water as fast as it pours out. But if you cut -off the supply of water from the upper lake -to the next lake, then the smaller lakes will in -time run dry. The same thing works with the -radioactivity. In this series headed by uranium, -as long as uranium is present all the -other elements below it are kept supplied so -that they don’t run out.”</p> -<p>“I understand that,” said Bill, “but how -do we use that to date a painting?”</p> -<p>“One of the pigments used by artists for -over 2000 years is known as lead white and it -is made from lead metal. The lead metal in -turn is extracted from a rock called lead ore, -in a process called smelting. The radioactive -lead, this lead-210 that I mentioned, behaves -like ordinary lead metal and goes along with -it.</p> -<p>“The radium, which has a fairly long -half-life, doesn’t follow the lead metal, but is -removed with other waste products in a -material called slag. Since the longer-lived -ancestor of the lead-210 is removed, the -<span class="pb" id="Page_15">15</span> -supply of lead-210 is cut off. (Or we can say -that one of the waterfalls is shut off.) The -lead-210 will then decay with its 22-year -half-life.”</p> -<div class="img" id="fig10"> -<img src="images/p08.jpg" alt="" width="800" height="587" /> -<p class="pcap"><i>The radioactive series that starts with uranium is like a series of lakes -connected by waterfalls. As long as uranium, the big one on top, has -water in it, the others will be full and the falls will keep flowing. But -when the first waterfall is shut off, the small lakes below it will run dry.</i></p> -</div> -<p>“I get it,” said Bill. “That means that -when you take a sample of old lead white -paint, there shouldn’t be any radioactive -lead-210 left.”</p> -<p>“That’s right. But that would only be true -if you removed all the radium. Actually, in -the smelting process it’s more usual to remove -only 90 or 95% of the radium. In that case, -the lead-210 would decay only until the -amount left would be equal to the small -amount of radium that wasn’t removed. In -<span class="pb" id="Page_16">16</span> -effect, this would be like shutting off only -part of the waterfall.”</p> -<p>“So what do you find,” asked Harley, “if -you measure the radioactivity in a sample of -lead white paint?”</p> -<p>“We find that if the paint is old, compared -to the 22-year half-life of the lead, let’s -say 100 years old or more, then the amount -of radioactivity from the lead-210 in the -sample of paint will be equal to the amount -of radioactivity from the radium in the -sample. But if the paint is modern, let’s say -only 20 years old or so, then the amount of -radioactivity from the lead-210 will be greater -than the amount of radioactivity from the -radium.”</p> -<p>Martin, who had been quiet through all -this explanation, finally spoke up. “Well, was -it finally tried out? How did it work?”</p> -<p>“Hundreds of samples were analyzed. -These samples were taken from paintings of -all ages, from some over 300 years old right up -to others only a couple of years old. The old -samples always showed equal amounts of -radioactivity from lead-210 and radium while -the modern ones always showed larger -amounts of radioactivity from lead-210 than -from radium. That meant that scientists had a -way of definitely telling if a lead white paint -was modern or not.</p> -<p>“Eventually, the method was tried on a -number of paintings believed to be by Van -Meegeren. Sure enough, every one of them -showed that the paint couldn’t possibly have -been more than 30 or 40 years old and that -Van Meegeren probably was telling the truth -<span class="pb" id="Page_17">17</span> -when he said that he had painted them. The -paintings certainly were not genuine Vermeers -from the 17th century.”</p> -<p>“Okay, Dad,” said Martin, “can we use -the method on any of the paintings we -found? Are any of these paintings supposed -to be old enough so that we can use this -test?”</p> -<p>“Not so fast. To find that out we have to -do a lot of checking first.”</p> -<p>“How do we go about it?” asked Bill.</p> -<p>“Let’s see now. There are nine paintings -in the box you found. The first thing we -should do is take them down to a museum or -gallery and let the art experts look at them. -Since we have a few weeks of vacation time -left, what do you say we take a trip down to -Washington, D. C., and show them to some -experts at the National Gallery of Art?”</p> -<p>Over the next few weeks quite a few -things happened to the boys and their paintings. -Three of them were discarded right away -because they were immediately recognized as -being copies of no value. Two were relatively -modern paintings with the signature Alfred -Sisley; if genuine, they were less than 100 -years old. The remaining four appeared to be -very old paintings. Two of them seemed to -correspond to paintings that disappeared during -the Second World War. Photographs and X -rays were taken and sent to the museum in -Holland, which had owned the missing pictures, -so that they could make a preliminary -examination.</p> -<div class="pb" id="Page_18">18</div> -<div class="img"> -<img src="images/p09.jpg" id="ncfig2" alt="uncaptioned" width="800" height="1023" /> -</div> -<dl class="undent pcap"><dt>Radioactivity of Lead-210</dt></dl> -<p class="pcapc">Lead-210 decaying with a half-life -of 22 years. When no radium is present -there is almost none left after 6 half-lives -or 132 years.</p> -<dl class="undent pcap"><dt>Radioactivity of Radium-226</dt></dl> -<p class="pcapc">Over the same period of time, a small amount of radium -decays very little because its half-life is about 1600 years.</p> -<dl class="undent pcap"><dt>Radioactivity of Radium 226</dt> -<dt>Radioactivity of Lead-210</dt></dl> -<p class="pcapc">But when lead-210 decays in the presence -of radium-226, the radioactivity of the lead-210 -only decreases until it is equal to the radioactivity -of the radium.</p> -<p>That left two that could have been old -but whose origins were unknown. A series of -simple chemical tests were begun on these and -the boys watched experts take very small -samples of paint for examination under the -microscope. After several months a list of the -pigments present in the paintings was prepared. -All the pigments found were typical of -old paintings and the ordinary examinations -and tests couldn’t prove whether the works -were old or not. Finally, it was decided that -<span class="pb" id="Page_19">19</span> -the only way to tell if these paintings were -truly old was to apply the test that Dad had -described to the boys.</p> -<p>The boys watched a painting restorer -remove samples of nearly white paint right at -the edge of the paintings. He worked carefully, -using a very sharp scalpel and a stereo-binocular -microscope, through which objects -appeared to be sixty times larger than they -really were. The sample of paint weighed -approximately twenty-thousandths of a gram. -The boys and their father took the samples to -a radiochemical laboratory where they -watched a radiochemist do the required analysis -for lead-210 and radium in the samples.</p> -<p>First the chemist dissolved the paint in -acetic acid. This removed the lead white from -the oil and from the small amounts of other -pigments in the paint. The solutions were -then heated and stirred with a silver disc -hanging in the liquid. After several hours the -disc still looked clean, but the chemist said -that a radioactive element, polonium-210, was -now plated onto the silver. Polonium-210 is a -member of the uranium series following the -lead-210, and a measurement of its radioactivity -would be an accurate measurement of -the radioactivity of lead-210.</p> -<p>The silver discs prepared from the two -samples were each placed in an instrument -called an alpha-particle spectrometer. This -instrument is extremely sensitive and can -measure the very small amounts of polonium-210 -prepared from the tiny sample of paint -that they started with.</p> -<div class="pb" id="Page_20">20</div> -<p>While the instruments were making the -measurements, which took a couple of days, -the chemist turned to the remaining solutions -and began the analyses for radium.</p> -<div class="img" id="fig11"> -<img src="images/p10.jpg" alt="" width="677" height="800" /> -<p class="pcap"><i>A painting being sampled under a stereo-binocular microscope.</i></p> -</div> -<div class="img" id="fig12"> -<img src="images/p10a.jpg" alt="" width="500" height="441" /> -<p class="pcap"><i>Lead white weighing -twenty-thousandths of a gram (20 milligrams). This is the amount -needed to measure lead-210 and radium-226 -to determine if the lead white is old.</i></p> -</div> -<p>In a series of chemical steps, he purified -the solutions, removing the lead and other -materials so that finally he had a small -amount of solution that contained little else -but the original radium and a very small -amount of barium (an element that he deliberately -added and one which is very similar to -radium in its chemical properties). By adding -dilute sulfuric acid, he prepared an insoluble -<span class="pb" id="Page_21">21</span> -material, barium sulfate, which was barely -visible suspended in the solution.</p> -<div class="img" id="fig13"> -<img src="images/p10c.jpg" alt="" width="509" height="799" /> -<p class="pcap"><i>Polonium plating apparatus. -A heated solution of lead -white in acetic acid is stirred -with silver discs for 4 to -8 hours.</i></p> -</div> -<div class="img" id="fig14"> -<img src="images/p10d.jpg" alt="" width="600" height="655" /> -<p class="pcap"><i>The disc above appears -clean after removal, but -on its surface it retains a -minute amount of polonium -which can be measured.</i></p> -</div> -<p>By forcing the solution through a special -thin plastic filter having tiny holes, the -particles of barium sulfate together with the -radium that had been in the solution were -caught on the surface of the filter. This was -mounted on a solid disc so that it too could -be placed in the alpha-particle spectrometer -for the measurement of radioactivity from the -radium.</p> -<p>Two weeks later the results were ready. -Dad, the boys, and one of the experts from -the museum met with the chemist to discuss -them. For one of the two paintings, the -<span class="pb" id="Page_22">22</span> -polonium-210 radioactivity was about ten -times that of the radium activity. The boys -were disappointed because this meant that -the painting could not have been 300 or 400 -years old as it first appeared to be.</p> -<div class="img" id="fig15"> -<img src="images/p11.jpg" alt="" width="1000" height="790" /> -<p class="pcap"><i>An alpha-particle spectrometer is used to measure the radioactivity of the radium and -polonium prepared from the lead white.</i></p> -</div> -<div class="img" id="fig16"> -<img src="images/p11a.jpg" alt="" width="534" height="800" /> -<p class="pcap"><i>A plastic disc on which is -cemented a filter containing a nearly invisible deposit of barium sulfate (BaSO₄) that -“carried” the radium.</i></p> -</div> -<p>But in the second painting the radioactivity -from the polonium-210 and from the -radium-226 were just about equal. That -meant that this painting was at least 100 years -old and, from its appearance, probably more. -The boys were excited.</p> -<p>“We have a really valuable painting!” said -Martin.</p> -<p>“Not so fast, boys,” cautioned Dad. “We -don’t know who painted it and we don’t -know exactly how old it is.”</p> -<p>The Gallery’s expert was happy too. He -believed that the second picture was a genuine -Dutch painting from the 17th century. It was -<span class="pb" id="Page_23">23</span> -a landscape and the artist might have been -Aelbert Cuyp.</p> -<div class="img" id="fig17"> -<img src="images/p11c.jpg" alt="" width="800" height="553" /> -<p class="pcap"><i>“The Maas at Dordrecht”, a genuine painting by Aelbert Cuyp.</i></p> -</div> -<p>“What do we do now?” asked Harley. -“How can we prove that the painting was -painted in Holland in the 17th century by -Cuyp?”</p> -<p>“There is a method now being developed,” -said Dad, “that could give us that kind -of information.”</p> -<p>“How does it work?” Martin asked.</p> -<div class="pb" id="Page_24">24</div> -<h2 id="c3"><span class="small">Who Was the Artist?</span></h2> -<p>“Do you know how criminals are caught -by using fingerprints?” asked Dad.</p> -<p>“Sure we do,” said Martin. “Each person -has a set of fingerprints that is different from -anyone else’s.”</p> -<p>Harley spoke up. “Did the artist leave his -fingerprints on the paintings?”</p> -<p>“Probably not,” said Dad. “Besides, they -would have been wiped off long ago. Also, -who knows what each artist’s fingerprints -were like?”</p> -<p>“Then what do you mean?” asked Bill.</p> -<p>“What I mean is, there is another kind of -‘fingerprint’ that scientists are just now learning -to use in all kinds of identification -problems. It’s not really a fingerprint, but it’s -just as distinctive as a real fingerprint.</p> -<p>“You see, in every material, no matter -how pure you try to make it, there are always -other substances contained in it in very, very -small quantities, which are there only by -chance. Usually the person making or using -that material doesn’t even know they are -there, and the quantities are so small they -don’t do any harm. During the last several -years, scientists have developed extremely -sensitive methods of analysis, which have -been applied to all kinds of problems.</p> -<p>“One such method is called neutron activation -analysis. In this method these small -amounts of impurities can be detected in tiny -samples of material. This is quite important -because only very small samples can be taken -from a precious painting without damaging it. -<span class="pb" id="Page_25">25</span> -Normally, a scientist or an art restorer takes -samples that are no bigger than the head of a -pin.”</p> -<p>“How can you do anything with a sample -that small?” asked Bill.</p> -<div class="img"> -<img src="images/p12.jpg" id="ncfig3" alt="uncaptioned" width="800" height="579" /> -</div> -<p>“With neutron activation analysis you can -do a great deal. To give you an example of -how sensitive this method is, think of a -bathtub containing 500 quarts of milk. Add 1 -drop of an acid containing a speck of gold -dissolved in it. After you mix the acid and -milk thoroughly, you won’t be able to tell by -looking at it that anything was added. But if -you take a thimble full of liquid out of the -bathtub, you can easily tell with neutron -activation analysis that gold was added to the -milk.</p> -<p>“Scientists call low concentrations of accidental -impurities ‘trace elements’, and the -amounts that are present are measured in -parts per million rather than percent. One -part per million is one ten-thousandth of a -percent.”</p> -<p>Bill spoke up again. “So how does that -make a fingerprint, Dad?”</p> -<div class="pb" id="Page_26">26</div> -<p>“It works this way. Suppose an artist used -lead white in several paintings. Now if the -lead white were absolutely pure it would -contain only lead, carbon, oxygen, and hydrogen. -But the lead white the artist used would -also contain very small quantities of other -elements, these trace elements that I spoke of. -In that particular batch of lead white, certain -trace elements will be present in a certain -quantity. The kind and amount of the trace -elements will be present in that exact pattern -only in that batch of lead white.</p> -<p>“Now suppose you analyze the lead white -from several paintings that you know were -painted by that particular artist, and you find -that there is silver, mercury, antimony, tin, -and barium in every one of the samples. Also, -each of these elements is always present in a -certain concentration. Suppose also, that you -have a painting which looks like it was -painted by that particular artist but you’re -not quite sure.</p> -<p>“Well, if you take a sample of lead white -from that unknown painting and you find -that the pattern of impurities is the same as in -the paintings you knew were genuine, then -the ‘fingerprints’ match. The chances of duplicating -impurities of this kind by pure -accident are extremely small, just about as -small as the chances of finding two people -with the same fingerprints. That’s why we call -this a ‘fingerprint method’.”</p> -<p>“That sounds like a good idea,” said -Harley. “Who thought it up?”</p> -<div class="pb" id="Page_27">27</div> -<table class="center"> -<tr class="th"><th colspan="6">x = one part per million (ppm)</th></tr> -<tr class="th"><th class="l" colspan="6">A known Rembrandt.</th></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">silver </td><td class="c">chromium </td><td class="c">zinc </td><td class="c">manganese </td><td class="c">iron </td><td class="c">cobalt</td></tr> -<tr><td colspan="6" class="c"><hr class="wide" /></td></tr> -<tr class="th"><th class="l" colspan="6">Unknown painting A</th></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">silver </td><td class="c">chromium </td><td class="c">zinc </td><td class="c">manganese </td><td class="c">iron </td><td class="c">cobalt</td></tr> -<tr><td colspan="6" class="c"><hr class="wide" /></td></tr> -<tr class="th"><th class="l" colspan="6">Unknown painting B</th></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">silver </td><td class="c">chromium </td><td class="c">zinc </td><td class="c">manganese </td><td class="c">iron </td><td class="c">cobalt</td></tr> -<tr><td colspan="6" class="c"><hr class="wide" /></td></tr> -<tr class="th"><th class="l" colspan="6">Known forgery</th></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c"> </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c"> </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c"> </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x </td><td class="c">x</td></tr> -<tr><td class="c">silver </td><td class="c">chromium </td><td class="c">zinc </td><td class="c">manganese </td><td class="c">iron </td><td class="c">cobalt</td></tr> -</table> -<p class="pcap"><i>Match the patterns of these lead white “fingerprints”. Unknown -painting A is</i> <b>not</b> <i>a Rembrandt; it</i> <b>is</b> <i>by the same forger who painted the -known forgery at the bottom. Unknown painting B is either by -Rembrandt, one of his fellow citizens, or one of his students using the -same paint.</i></p> -<div class="pb" id="Page_28">28</div> -<p>“It was thought of many times by many -people. But, it’s never been used for identifying -paintings. In 1964 in the Netherlands, two -scientists, named Houtman and Turkstra, -analyzed about 40 different samples of lead -white, 20 of which came from Dutch and -Flemish paintings. The rest were samples of -lead white not taken from paintings but -obtained directly from the manufacturers. -They analyzed these samples for different -elements. These included silver, mercury, -chromium, manganese, tin, antimony, and a -couple of others.</p> -<p>“They found that the concentrations of -these elements in the lead white from all the -old Dutch and Flemish paintings were very -similar. And the trace element concentrations -were quite different in the modern lead white -samples analyzed in the same way. At the -time, they presumed that it was because the -lead white in the paintings was manufactured -so long ago. They may have been right to a -certain extent.</p> -<p>“For example, they found that in all the -old paintings there were from 10 to 30 parts -per million of silver in the lead white, while in -the modern samples of this pigment there -were generally less than 10 parts per million -of silver. All of them had been painted before -the 19th century, and all the samples of pure -lead white were manufactured during the -latter part of the 19th century or during the -20th century. They believed that the reason -the silver concentration was lower in the more -modern material was because during the 19th -century, lead refiners were doing a better job -of removing all the valuable silver from lead.</p> -<div class="pb" id="Page_29">29</div> -<div class="img" id="fig18"> -<img src="images/p14.jpg" alt="" width="800" height="459" /> -<p class="pcap"><i>Silver concentrations in lead white. The concentrations generally -decreased after the middle 1800s. Notice also how the concentrations -were very similar for all the older paintings (before 1700) which were -Dutch or Flemish.</i></p> -</div> -<p>“However, in 1967 in Germany, two -men, named Lux and Braunstein, discovered -that in some old paintings produced -in Italy, lead white also contained low quantities -of silver just like modern material. They -believed that the higher concentrations of -silver in lead white were typical of Dutch and -Flemish painters while the lower concentrations -were typical of Italian paintings of -about the same age.</p> -<p>“The whole case is still unsettled because -not enough measurements have been made to -show how reliable this method can be. That -is, no one knows if samples of paint from -several paintings by one artist would all have -the same pattern of impurities in the same -pigment. It may be that of the many pigments -present in an artist’s paintings only a few will -<span class="pb" id="Page_30">30</span> -be suitable for use in this ‘fingerprinting’ -method.”</p> -<div class="img" id="fig19"> -<img src="images/p15.jpg" alt="" width="559" height="800" /> -<p class="pcap"><i>Quartz vials (right) containing -samples are sealed -in the aluminum can on -the left. They are then -bombarded with neutrons -in a reactor like the one in -the picture below.</i></p> -</div> -<p>“It sounds complicated,” said Bill.</p> -<p>“It is, and it’s going to take years of work -before the method is proven, if it is at all. It -may turn out that you can’t tell one artist -from another, but only groups of artists like -17th century Dutch painters or 19th century -English painters.”</p> -<p>“Tell us something about neutron activation -analysis,” said Martin. “How do you -measure such small amounts of impurities?”</p> -<p>“The best way to tell you how this works -is to show you. How would you boys like to -visit a laboratory where neutron activation -analysis is being done?”</p> -<p>“Do you have to ask?” said Harley. “Of -course we would!”</p> -<p>A few weeks later it was all arranged. At a -laboratory close by a nuclear reactor, the boys -watched a radiochemist place a few specks of -material inside small quartz tubes that were -then sealed. The tubes were put in an aluminum -can and placed in the nuclear reactor. -The can was fastened on the end of a long -pole that was then submerged in a deep pool -of water. At the bottom of the pool the boys -could see a bright blue glow.</p> -<div class="img" id="fig20"> -<img src="images/p15b.jpg" alt="" width="580" height="800" /> -<p class="pcap"><i>This type of nuclear reactor -is used for neutron -activation analysis.</i></p> -</div> -<p>“So that’s what a nuclear reactor looks -like!” said Bill.</p> -<p>“Yes,” said Dad. “Where you see the blue -glow you can also see rows of fuel elements. -Each one contains slugs of uranium encased in -aluminum. This is one of a number of -different types of reactors. But every nuclear -reactor is arranged so that the uranium atoms -<span class="pb" id="Page_31">31</span> -divide (or fission) many, many times each -second.</p> -<p>“When this happens, heat is produced that -is carried away by the water, and also many, -many free neutrons are produced. Those -samples, placed down next to the reactor in -the bottom of the pool are being bombarded -by the neutrons, and some of the elements in -the samples absorb the neutrons and become -radioactive.”</p> -<p>After a while the samples were removed -and carried back to the laboratory in a lead -box. A short while later, the radiochemist -opened the aluminum can, broke open the -quartz capsules, and removed the samples for -analysis. The boys watched the chemist -mount each sample on a card and take it to a -room where there was equipment for measuring -radioactivity.</p> -<div class="img" id="fig21"> -<img src="images/p15c.jpg" alt="" width="800" height="376" /> -<p class="pcap"><i>Gamma-ray spectrometer. The sample to be measured is placed on a -stand over a gamma-ray detector. The pulse-height analyzer is a device -that sorts electrical impulses from the detector according to the energy -of the gamma rays causing the impulses. The screen displays the -gamma-ray spectrum and the electric typewriter automatically types -out the data collected when the measurement is complete.</i></p> -</div> -<div class="pb" id="Page_32">32</div> -<p>One by one the samples were placed -inside a shield consisting of a big pile of lead -bricks. When the heavy door was opened, the -boys could see a metal can inside the shield, -which housed a detector (called a lithium-drifted -germanium detector) that measured -the gamma rays emitted by the sample. As -each sample was placed near the detector the -chemist turned on a gamma-ray spectrometer -to which the detector was connected.</p> -<p class="pcapc">A tiny sample of lead white <img class="inline" src="images/x1.png" alt="sample" width="44" height="28" /> -is sealed in a quartz vial <img class="inline" src="images/x2.png" alt="vial" width="56" height="32" /> which -is bombarded with neutrons in a reactor.</p> -<div class="img"> -<img src="images/p16.jpg" id="ncfig4" alt="uncaptioned" width="333" height="234" /> -</div> -<p class="pcapc">Many of the atoms become radioactive, emitting gamma rays.</p> -<div class="img"> -<img src="images/p16c.jpg" id="ncfig5" alt="uncaptioned" width="700" height="331" /> -</div> -<p class="pcapc">The sample is placed in a gamma-ray spectrometer and the gamma rays -are separated according to their energy.</p> -<div class="img"> -<img src="images/p16d.jpg" id="ncfig6" alt="uncaptioned" width="600" height="391" /> -</div> -<dl class="undent pcap"><dt>Gamma-ray spectrum</dt> -<dd>Copper</dd> -<dd>Zinc</dd> -<dd>Antimony</dd> -<dd>Lead</dd> -<dd>Silver</dd> -<dd>Height</dd> -<dd>Antimony</dd></dl> -<p class="pcapc">The location (energy) of -each peak indicates what -is present and the height -indicates how much!</p> -<div class="pb" id="Page_33">33</div> -<div class="img" id="fig22"> -<img src="images/p16e.jpg" alt="" width="1000" height="718" /> -<p class="pcap"><i>A gamma-ray spectrum as it appears on the screen of a pulse-height -analyzer. The gamma-ray peaks are marked with the name of the -element whose radioactive isotope emits the gamma ray; two for cobalt -and zinc and one for cesium.</i></p> -</div> -<p>There, on what looked like a small television -screen, flashes of light appeared that -gradually formed a curve with many peaks -and valleys. After a few minutes the spectrometer -was stopped and an electric typewriter -automatically typed out rows and -columns of numbers.</p> -<p>The chemist explained, “This curve, -which you see on the screen, is a gamma-ray -spectrum and tells us what elements are in the -sample. The typed-out data give us an accurate -measure of the shape of the curve on -the screen. By measuring the gamma-rays’ -energies we know what elements in the -sample were made radioactive. The height of -<span class="pb" id="Page_34">34</span> -each gamma-ray peak tells us how much of -that element is present in the sample.</p> -<p>“That gives us the information we need to -calculate the concentrations of the small -quantities of materials in our samples. We can -do this because at the same time I irradiated a -set of standards. Standards are materials that -are just like the samples except that they -contain known amounts of the impurities I -am trying to measure.”</p> -<p>As the boys were leaving the laboratory, -the chemist apologized for not having enough -time to explain the activation analysis procedure -more thoroughly, but he did give the -boys a list of books to read on the subject of -radioactivity and radioisotopes.<a class="fn" id="fr_2" href="#fn_2">[2]</a> They -thanked him for his help.</p> -<p>During the ride home, they discussed the -paintings that were still unproven.</p> -<p>“It’s too bad that the method of activation -analysis fingerprinting hasn’t been fully -developed yet,” said Dad.</p> -<p>“Yes,” said Bill. “Then we could prove -whether or not that last old painting was -really by Aelbert Cuyp as the expert from the -gallery believed. But what about those paintings -that we found in the box that were not -so old?”</p> -<p>“Well,” said Dad, “if the activation analysis -method were workable, we might be able -to prove if they were painted by Alfred -Sisley. Meanwhile, until the method is really -developed we don’t know if we can do it that -way or not.”</p> -<div class="pb" id="Page_35">35</div> -<p>“So what do we do now?” asked Martin.</p> -<p>“We’ll have to wait until scientists can -thoroughly investigate this method and -several others that they’re working on.”</p> -<p>“Other methods!” exclaimed Bill. “What -other methods?”</p> -<div class="img" id="fig23"> -<img src="images/p17.jpg" alt="" width="1200" height="956" /> -<p class="pcap"><i>“The Banks of the Oise”, a genuine painting by Alfred Sisley.</i></p> -</div> -<div class="pb" id="Page_36">36</div> -<h2 id="c4"><span class="small">Other New Tools for Art Authentication</span></h2> -<p>“There are several new tools that scientists -are working on now,” said Dad. “These -involve methods that have been developed by -scientists for other purposes, but are now -being explored for use in authenticating -works of art.</p> -<p>“For example, in Los Angeles, the county -museum purchased an instrument known as a -Spark Source Mass Spectrometer. Like activation -analysis, this instrument will also measure -small traces of impurities, but they have -just set that up and it will take them years to -explore the use of it for the type of problem -we have been discussing.</p> -<p>“X-ray diffraction is another method that -has been around for quite awhile but hasn’t -been used much for art identification until -recently. With X-ray diffraction, samples of -pigments can be identified by the pattern -formed when X rays are bent by passing -through the sample of pigment.”</p> -<p>“How’s that?” asked Harley.</p> -<p>“There are 3 or 4 different compounds -with about the same chemical composition as -lead white. Chemically, they are almost impossible -to distinguish. But with X-ray diffraction, -a chemist can easily tell them apart. The -hope is that the type of lead white will -indicate how it was manufactured. Until the -middle of the 19th century, lead white was -produced mainly by packing strips of lead in -clay pots with a little vinegar in the bottom. -The clay pots were stacked in a large building -with layers of decaying organic matter on the -<span class="pb" id="Page_37">37</span> -floor. The building was sealed for several -weeks during which time the lead corroded in -the fumes and became covered with a white -substance. The white substance, lead white, -was scraped off, ground, and washed to make -the pigment.</p> -<p>“But, in the 19th century, when -people began to learn more about chemistry, -they looked for faster ways of -making lead white and some of these -methods produced a lead white of somewhat -different composition. By using X-ray diffraction, -chemists now hope that they can tell -how the lead white was manufactured. This -may provide another means of dating the lead -white in a painting.”</p> -<p>“Are there any other methods?” asked -Harley.</p> -<div class="img" id="fig24"> -<img src="images/p18.jpg" alt="" width="694" height="800" /> -<p class="pcap"><i>The stack process for making -lead white. Rows of -clay pots containing lead -and vinegar are packed to -the ceiling of the building, -and fermenting tanbark on -the floor produces carbon -dioxide and heat. The -fumes of vinegar and the -carbon dioxide corrode -the lead in 2 to 4 months, -and the corrosion is lead -white.</i></p> -</div> -<p>“Yes, isotope mass spectrometry is one. -All lead consists of 4 different isotopes or -atoms of different weights. Three of these 4 -<span class="pb" id="Page_38">38</span> -are the end products of a radioactive decay -chain. Depending upon the history of the -rock formation in which the lead ore occurred, -the relative amounts of the lead -isotopes vary in a special way. In other words, -if we know the different amounts of lead -isotopes in the world’s lead ore deposits, and -we have a sample of lead white from a -painting, we can tell from which deposit the -lead, which formed the lead white, came. If, -for example, we find that the isotope pattern -in a sample from a painting is the same as in -lead ore from Australia, then the painting -can’t be very old because lead white wasn’t -produced from lead mined in Australia until -about 100 years ago.”</p> -<div class="img" id="fig25"> -<img src="images/p19.jpg" alt="" width="800" height="688" /> -<p class="pcap"><i>X-ray diffraction patterns from three different lead compounds that -might occur in lead white. The middle one is the ideal lead white -produced for over 2000 years. While some of the bottom compound -may be found mixed with it, the compound shown at the top is only a -20th-century invention.</i></p> -</div> -<dl class="undent pcap"><dt>4PbCO₃ · 2PB(OH)₂ · PbO</dt> -<dt>2PbCO₃ · PB(OH)₂</dt> -<dt>PbCO₃</dt></dl> -<div class="pb" id="Page_39">39</div> -<p>“How do you measure lead isotopes?” -asked Harley.</p> -<p>“With an instrument called a mass spectrometer. -This instrument is capable of -separating the lead isotopes. First, the atoms -of lead in the sample are electrically charged -and ‘fired’ in a beam down the length of a -tube between the poles of a strong magnet. -There, the charged atoms (or ions) in the -beam are deflected by different amounts -according to how heavy they are. Thus the -different isotopes are separated. This method -is also still being studied and, although it -shows great promise, it will be some time -before it can solve problems of art identification. -Also the study of the natural variation in -isotopes of other elements, such as sulfur, -is useful for identification of other pigments -as well.</p> -<div class="img" id="fig26"> -<img src="images/p19a.jpg" alt="" width="800" height="430" /> -<p class="pcap"><i>Diagram of a simple mass spectrometer. The ionized atoms of lead -travel in a beam at the same speed. The heavier atoms bend less than -the lighter ones when the beam passes the magnet. Thus two beams -emerge instead of one. Actually there are four isotopes of lead so there -will be four beams.</i></p> -</div> -<div class="pb" id="Page_40">40</div> -<div class="img" id="fig27"> -<img src="images/p20.jpg" alt="" width="588" height="792" /> -<p class="pcap"><i>“Agostina”, a genuine -painting by Jean Baptiste -Camille Corot.</i></p> -</div> -<p>“Another new method that shows great -promise has been developed, but this one is -not applicable to the paintings that you boys -found in the box.”</p> -<p>“Why not?” asked Bill.</p> -<p>“Since the Second World War, the art -forgery business has been growing rapidly. -For example, it has been said that of the 2000 -pictures that Corot, a 19th century Frenchman, -is known to have painted, more than -5000 of them are in the United States. This -may be only a humorous exaggeration, but a -large number of forgeries have been produced -in the last several years. These are usually -supposed to be paintings that are less than -100 years old. Present-day forgers like to -forge paintings that aren’t very old because -it’s easier to get away with. Now this new -method, which will detect such recent forgeries, -is based upon the presence of carbon-14, a -radioactive isotope of carbon, in our atmosphere -and in all things that grow on our -planet.</p> -<p>“Ordinarily, carbon-14 is produced only -by cosmic rays, and its concentrations in the -atmosphere and in growing things would -remain at a constant level. But since the -middle of the 1950s the testing of nuclear -weapons has increased the amount of radioactive -carbon in our atmosphere by quite a -bit. Many artist’s materials, such as linseed oil, -canvas, paper, and so on, come from plants or -animals, and so will contain the same concentrations -of carbon-14 as the atmosphere -up to the time that the plant or animal dies.</p> -<div class="pb" id="Page_41">41</div> -<p>“Therefore, linseed oil (from the flax -plant), for example, produced during the last -few years will have a much greater concentration -of carbon-14 in it than linseed oil -produced more than 20 years ago. Scientists -at Carnegie-Mellon University have shown -that this method will work. It is only a matter -of making the measurements on the small -samples available from presumably valuable -paintings.”</p> -<div class="img" id="fig28"> -<img src="images/p20a.jpg" alt="" width="1000" height="928" /> -<p class="pcap"><i>The changing concentrations of carbon-14 in our atmosphere. High -levels of carbon-14 in linseed oil and other painting materials will -indicate that a work of art is only a few years old.</i></p> -</div> -<dl class="undent pcap"><dt>Carbon-14 radioactivity</dt> -<dd>Older materials contain less as the carbon-14 decays away.</dd> -<dd>In this period, decrease is due to the burning of large quantities of coal and oil as industry grew. This diluted the newly formed carbon-14.</dd> -<dd>Increases due to testing of atomic weapons in the atmosphere.</dd> -<dt>Carbon-14 produced by cosmic rays only</dt> -<dd>Neutron → Nitrogen → Carbon-14 + proton</dd> -<dd>Carried down by rain in carbon dioxide</dd></dl> -<p>“There are also a number of other -methods being studied including the use of -Messbauer Effect Spectroscopy to study pigments -<span class="pb" id="Page_42">42</span> -that contain iron, thermoluminescent -dating of pottery and terra-cotta statuary, -X-ray fluorescence analysis as a general tool, -and neutron autoradiography as a means of -studying the technique of artists. You can -read all about them if you wish.”<a class="fn" id="fr_3" href="#fn_3">[3]</a></p> -<p>“It sounds like forgers are going to have a -tough time in the future,” said Harley.</p> -<p>“That’s right. It may even turn out that -producing forgeries to pass all these new tests -will be so difficult and expensive that forgers -will stop trying.”</p> -<h2 id="c5"><span class="small">One Mystery Solved</span></h2> -<p>A year later an important letter arrived at -the boys’ house. Dad opened it, read it -quickly, and said, “Good news, boys! This -letter is from the Dutch government. Remember -those two paintings that we thought -might have been stolen from a Dutch -museum?”</p> -<p>“Yes,” said Bill.</p> -<p>“Well, it seems that after a year of -studying them, the Dutch have decided that -they really are the paintings that were -stolen.”</p> -<p>“That is good news,” said Harley. “At -least we know that two of the paintings we -found are genuine.”</p> -<p>“What are they going to do with them?” -asked Martin.</p> -<p>“Of course, they have to go back to their -original owners. But this letter says that the -<span class="pb" id="Page_43">43</span> -Dutch government wants us to come to -Holland as their guests as a reward for finding -those paintings.”</p> -<div class="img" id="fig29"> -<img src="images/p21.jpg" alt="" width="800" height="452" /> -<p class="pcap"><i>These two paintings “The Lacemaker” and “The Smiling Girl” were -thought to have been by Vermeer. A series of tests, including some of -those described in this booklet, showed that the paintings are fairly old. -However, some of the materials used are not typical of Vermeer, and the -pictures are now thought to have been painted by a follower of the artist.</i></p> -</div> -<p>“That’s great!” said Bill. “Looks like -we’re getting something out of finding that -box after all.”</p> -<p>“Yes,” said Dad. “And don’t forget the -other unidentified paintings may also be -genuine. We’ve proved that one is a fake, the -experts believe that three of the others are -copies, and then there are the two that might -be Sisleys and are only waiting for a method -to prove it. And we have one more that -science managed to prove was really old. I’m -sure that in a few years methods will be -developed to tell us exactly who painted it.</p> -<p>“And now let’s make arrangements for -our trip to Holland.”</p> -<div class="pb" id="Page_44">44</div> -<h2 id="c6"><span class="small">Reading List</span></h2> -<p class="revint"><i>About Atomic Power for People</i>, Edward and -Ruth S. Radlauer, Childrens Press, Chicago, -Illinois 60607, 1960, 47 pp., $2.50. Grades -5-9.</p> -<p class="revint"><i>All About the Atom</i>, Ira M. Freeman, Random -House, Inc., New York 10022, 1955, -146 pp., $2.50. Grades 4-6.</p> -<p class="revint"><i>Atoms at Your Service</i>, Henry A. Dunlap and -Hans N. Tuch, Harper and Row, Publishers, -New York 10016, 1957, 167 pp., $4.00. -Grades 7-9.</p> -<p class="revint"><i>Carbon-14 and Other Science Methods that -Date the Past</i>, Lynn and Gray Poole, -McGraw-Hill Book Company, New York -10036, 1961, 160 pp., $3.95. Grades 9-12.</p> -<p class="revint"><i>Experiments with Atomics</i> (revised edition), -Nelson F. Beeler and Franklyn M. Branley, -Crowell Collier and Macmillan, Inc., New -York 10022, 1965, 160 pp., $3.50. Grades -5-8.</p> -<p class="revint"><i>The Fabulous Isotopes: What They Are and -What They Do</i>, Robin McKown, Holiday -House, Inc., New York 10022, 1962, -189 pp., $4.50. Grades 7-10.</p> -<p class="revint"><i>Inside the Atom</i> (revised edition), Isaac -Asimov, Abelard-Schuman, Ltd., New York -10019, 1966, 197 pp., $4.00. Grades 7-10.</p> -<p class="revint"><i>Introducing the Atom</i>, Roslyn Leeds, Harper -and Row, Publishers, New York 10016, -1967, 224 pp., $3.95. Grades 7-9.</p> -<p class="revint"><i>Our Friend the Atom</i>, Heinz Haber, Golden -Press, Inc., New York 10022, 1957, -165 pp., $4.95 (out of print but available -through libraries); $0.35 (paperback) from -<span class="pb" id="Page_45">45</span> -Dell Publishing Company, Inc., New York -10017. Grades 7-9.</p> -<p class="revint"><i>Radioisotopes</i>, John H. Woodburn, J. B. -Lippincott Company, Philadelphia, Pennsylvania -19105, 1962, 128 pp., $3.50. Grades -7-10.</p> -<p class="revint"><i>The Story of Atomic Energy</i>, Laura Fermi, -Random House, Inc., New York 10022, -1961, 184 pp., $1.95. Grades 7-11.</p> -<p class="revint"><i>The Useful Atom</i>, William R. Anderson and -Vernon Pizer, The World Publishing Company, -New York 10022, 1966, 185 pp., -$5.75. Grades 7-12.</p> -<p class="revint"><i>Working with Atoms</i>, Otto R. Frisch, Basic -Books, Inc., Publishers, New York 10016, -1965, 96 pp., $3.50. Grades 9-12.</p> -<h3>Footnotes</h3> -<div class="fnblock"><div class="fndef"><a class="fn" id="fn_1" href="#fr_1">[1]</a>It is called this because 210 is the total number of -protons and neutrons in its nucleus. -</div><div class="fndef"><a class="fn" id="fn_2" href="#fr_2">[2]</a>See the reading list on <a href="#Page_44">page 44</a>. -</div><div class="fndef"><a class="fn" id="fn_3" href="#fr_3">[3]</a>See <i>Secrets of the Past: Nuclear Science and Archaeology</i>, -which is listed on the <a href="#Page_47">inside back cover</a> of this booklet. -</div> -</div> -<h3 id="c7">PHOTO CREDITS</h3> -<p><a href="#cover">Cover</a> courtesy Groninger Museum voor stad en Lande</p> -<div class="forcesf"> -<table class="center"> -<tr class="th"><th>Page</th></tr> -<tr><td class="c"><a href="#Page_5">5</a> </td><td class="l">Yale Joel, <i>Life</i> magazine, copyright © Time, Inc.</td></tr> -<tr><td class="c"><a href="#Page_6">6</a> </td><td class="l">Her Majesty the Queen, copyright © reserved</td></tr> -<tr><td class="c"><a href="#Page_7">7</a> & <a href="#Page_8">8</a> </td><td class="l">Ullstein Bilderdienst</td></tr> -<tr><td class="c"><a href="#Page_10">10</a> </td><td class="l">Rijksmuseum, Amsterdam</td></tr> -<tr><td class="c"><a href="#Page_23">23</a> </td><td class="l">National Gallery of Art, Washington, D. C., Andrew Mellon Collection</td></tr> -<tr><td class="c"><a href="#Page_35">35</a> & <a href="#Page_40">40</a> </td><td class="l">National Gallery of Art, Washington, D. C., Chester Dale Collection</td></tr> -<tr><td class="c"><a href="#Page_43">43</a> </td><td class="l">National Gallery of Art, Washington, D. C., Andrew Mellon Collection</td></tr> -</table> -</div> -<p class="jr1"><span class="ss"><span class="smallest">★ U.S. GOVERNMENT PRINTING OFFICE: 1974—747-556/15</span></span></p> -<div class="pb" id="Page_47">47</div> -<hr class="dwide" /> -<p>The U. S. Atomic Energy Commission publishes this series of information -booklets for the general public. The booklets are listed below by subject -category.</p> -<p>If you would like to have copies of these booklets, please write to the -following address for a booklet price list:</p> -<div class="verse"> -<p class="t0">USAEC—Technical Information Center</p> -<p class="t0">P. O. Box 62</p> -<p class="t0">Oak Ridge, Tennessee 37830</p> -</div> -<p>School and public libraries may obtain a complete set of the booklets -without charge. These requests must be made on school or library stationery.</p> -<table class="center"> -<tr class="th"><th class="l" colspan="2">Chemistry</th></tr> -<tr><td class="l">IB-303 </td><td class="l">The Atomic Fingerprint: Neutron Activation Analysis</td></tr> -<tr><td class="l">IB-301 </td><td class="l">The Chemistry of the Noble Gases</td></tr> -<tr><td class="l">IB-302 </td><td class="l">Cryogenics: The Uncommon Cold</td></tr> -<tr><td class="l">IB-304 </td><td class="l">Nuclear Clocks</td></tr> -<tr><td class="l">IB-306 </td><td class="l">Radioisotopes in Industry</td></tr> -<tr><td class="l">IB-307 </td><td class="l">Rare Earths: The Fraternal Fifteen</td></tr> -<tr><td class="l">IB-308 </td><td class="l">Synthetic Transuranium Elements</td></tr> -<tr class="th"><th class="l" colspan="2">Biology</th></tr> -<tr><td class="l">IB-101 </td><td class="l">Animals in Atomic Research</td></tr> -<tr><td class="l">IB-102 </td><td class="l">Atoms in Agriculture</td></tr> -<tr><td class="l">IB-105 </td><td class="l">The Genetic Effects of Radiation</td></tr> -<tr><td class="l">IB-110 </td><td class="l">Preserving Food with Atomic Energy</td></tr> -<tr><td class="l">IB-106 </td><td class="l">Radioisotopes and Life Processes</td></tr> -<tr><td class="l">IB-107 </td><td class="l">Radioisotopes in Medicine</td></tr> -<tr><td class="l">IB-109 </td><td class="l">Your Body and Radiation</td></tr> -<tr class="th"><th class="l" colspan="2">The Environment</th></tr> -<tr><td class="l">IB-201 </td><td class="l">The Atom and the Ocean</td></tr> -<tr><td class="l">IB-202 </td><td class="l">Atoms, Nature, and Man</td></tr> -<tr><td class="l">IB-414 </td><td class="l">Nature’s Invisible Rays</td></tr> -<tr class="th"><th class="l" colspan="2">General Interest</th></tr> -<tr><td class="l">IB-009 </td><td class="l">Atomic Energy and Your World</td></tr> -<tr><td class="l">IB-010 </td><td class="l">Atomic Pioneers—Book 1: From Ancient Greece to the 19th Century</td></tr> -<tr><td class="l">IB-011 </td><td class="l">Atomic Pioneers—Book 2: From the Mid-19th to the Early 20th Century</td></tr> -<tr><td class="l">IB-012 </td><td class="l">Atomic Pioneers—Book 3: From the Late 19th to the Mid-20th Century</td></tr> -<tr><td class="l">IB-002 </td><td class="l">A Bibliography of Basic Books on Atomic Energy</td></tr> -<tr><td class="l">IB-004 </td><td class="l">Computers</td></tr> -<tr><td class="l">IB-008 </td><td class="l">Electricity and Man</td></tr> -<tr><td class="l">IB-005 </td><td class="l">Index to AEC Information Booklets</td></tr> -<tr><td class="l">IB-310 </td><td class="l">Lost Worlds: Nuclear Science and Archeology</td></tr> -<tr><td class="l">IB-309 </td><td class="l">The Mysterious Box: Science and Art</td></tr> -<tr><td class="l">IB-006 </td><td class="l">Nuclear Terms: A Glossary</td></tr> -<tr><td class="l">IB-013 </td><td class="l">Secrets of the Past: Nuclear Energy Applications in Art and Archaeology</td></tr> -<tr><td class="l">IB-017 </td><td class="l">Teleoperators: Man’s Machine Partners</td></tr> -<tr><td class="l">IB-014, 015, & 016 </td><td class="l">Worlds Within Worlds: The Story of Nuclear Energy Volumes 1, 2, and 3</td></tr> -<tr class="th"><th class="l" colspan="2">Physics</th></tr> -<tr><td class="l">IB-401 </td><td class="l">Accelerators</td></tr> -<tr><td class="l">IB-402 </td><td class="l">Atomic Particle Detection</td></tr> -<tr><td class="l">IB-403 </td><td class="l">Controlled Nuclear Fusion</td></tr> -<tr><td class="l">IB-404 </td><td class="l">Direct Conversion of Energy</td></tr> -<tr><td class="l">IB-410 </td><td class="l">The Electron</td></tr> -<tr><td class="l">IB-405 </td><td class="l">The Elusive Neutrino</td></tr> -<tr><td class="l">IB-416 </td><td class="l">Inner Space: The Structure of the Atom</td></tr> -<tr><td class="l">IB-406 </td><td class="l">Lasers</td></tr> -<tr><td class="l">IB-407 </td><td class="l">Microstructure of Matter</td></tr> -<tr><td class="l">IB-415 </td><td class="l">The Mystery of Matter</td></tr> -<tr><td class="l">IB-411 </td><td class="l">Power from Radioisotopes</td></tr> -<tr><td class="l">IB-413 </td><td class="l">Spectroscopy</td></tr> -<tr><td class="l">IB-412 </td><td class="l">Space Radiation</td></tr> -<tr class="th"><th class="l" colspan="2">Nuclear Reactors</th></tr> -<tr><td class="l">IB-501 </td><td class="l">Atomic Fuel</td></tr> -<tr><td class="l">IB-502 </td><td class="l">Atomic Power Safety</td></tr> -<tr><td class="l">IB-513 </td><td class="l">Breeder Reactors</td></tr> -<tr><td class="l">IB-503 </td><td class="l">The First Reactor</td></tr> -<tr><td class="l">IB-505 </td><td class="l">Nuclear Power Plants</td></tr> -<tr><td class="l">IB-507 </td><td class="l">Nuclear Reactors</td></tr> -<tr><td class="l">IB-510 </td><td class="l">Nuclear Reactors for Space Power</td></tr> -<tr><td class="l">IB-508 </td><td class="l">Radioactive Wastes</td></tr> -<tr><td class="l">IB-511 </td><td class="l">Sources of Nuclear Fuel</td></tr> -<tr><td class="l">IB-512 </td><td class="l">Thorium and the Third Fuel</td></tr> -</table> -<div class="img"> -<img src="images/p30.jpg" id="ncfig7" alt="AEC logo" width="310" height="318" /> -</div> -<p class="center"><span class="rubric ss">U. 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