How Nuclear Bomb Tests Are Helping to Identify Art Forgeries

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How can you tell if a painting is a modern forgery? Mid-20th-century nuclear bomb tests may hold a clue.

For years, scientists have been refining techniques to determine the age of a painting using radiocarbon dating and the lingering effects of the tests. Now, a team of researchers has dated one such artwork using a paint chip the size of a poppy seed, according to a studypublished on Monday in The Proceedings of the National Academy of Sciences.

“It’s an amazing technical achievement,” said Greg Hodgins, a professor at the University of Arizona who oversees a lab dedicated to radiocarbon dating and was not involved in the study.

The ‘bomb peak’

Developed in the 1940s, radiocarbon dating allows scientists to determine the age of a wide range of materials — including fossils, cave paintings, parchment and even human remains — by examining the types of carbon atoms they contain.

Atoms of a single element but of different masses are known as isotopes. The carbon 12 and carbon 13 isotopes are stable, while carbon 14 is unstable. The mix of those isotopes is consistent among living things, but once organic matter dies its carbon 14 atoms decay. As a result, scientists can determine the age of dead organic matter up to tens of thousands of years old by calculating the ratio of those carbon isotopes.

But that formula was drastically disrupted a little over half a century ago, with the advent of nuclear testing.

Carbon 14 is naturally created when high-energy cosmic rays collide with nitrogen atoms in the atmosphere. But the powerful aboveground nuclear bomb tests of the mid-1900s created even more carbon 14 isotopes out of that atmospheric nitrogen. In fact, so much carbon 14 had been created in the decade or so leading up to the signing of the partial nuclear test ban treaty of 1963 that levels in the atmosphere virtually doubled.

“This bomb peak is really a unique signature,” said Laura Hendriks, a doctoral candidate at ETH Zurich in Switzerland and the lead author of the study, referring to the spike in atmospheric carbon 14. “It can be used in so many different fields, it’s just unbelievable, although it’s not a good thing.”

The effect of the bomb tests was akin to advancing a clock, according to Professor Hodgins. “In cosmic carbon dating terms, it’s kind of like moving 5,000 years into the future,” he said.

That increase in carbon 14 was reflected in anything that lived or died after 1963, including wood and fibers that might make up the support or canvas of a modern work of art or the organic matter used to bind pigments in modern paint.

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