“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.