Researchers from ETH Zurich have refined a process that can detect modern fakes of paintings by measuring excessive levels of the isotope carbon-14 released into the atmosphere through nuclear testing in the 20th century. The new method requires significantly smaller samples of paint than was previously necessary, with a case study demonstrating accuracy dating from a single paint particle weighing under 200 micrograms.

For a couple of decades leading up to the Limited Test Ban treaty of 1963, hundreds of nuclear bombs were tested in Earth's atmosphere. These tests ultimately doubled the amount of an isotope called carbon-14 in our environment. This increased volume of carbon-14 can be found in every organic material that has been generated since the 1960s.

For some time the idea of tracking art forgeries by measuring levels of carbon-14 in their materials has been suggested, however it was fundamentally unfeasible until recently due to the volume of samples required for the measurement. At the same time, art forgers have become more and more savvy to these potential identification techniques and deployed increasingly sophisticated methods to evade detection. Not only do some forgeries now utilize old wooden frames, but some fakers even scrape paint off old artworks and re-use it.

In the past scientists have needed anywhere from several grams to 100 milligrams of paint samples to be able to effectively determine the presence of excessive carbon-14 levels. If old samples of paint have been mixed with a modern binder this means any tested artwork would inevitably be significantly damaged in order to obtain enough of a sample to trace its authenticity. However, the team from ETH Zurich has, for the first time, managed to improve detection methods so a sample of paint no more than 200 micrograms is needed to measure carbon-14 levels.

To test this new method the scientists sampled a famous known forgery of a painting allegedly created in the mid-19th century but actually produced by an infamous forger in the 1980s. Two microsamples from the painting were analyzed, one tiny fiber from the canvas, and a single paint particle weighing around 160 micrograms.

Carbon dating of the canvas fiber was consistent with the alleged age of the painting, suggesting the forger cleverly utilized an old canvas to create the fake. However, the tiny paint particle revealed the truth, with excessive carbon-14 levels suggesting the organic materials used to create the binding agent in the paint were harvested sometime in the second half of the 20th century.

This isn't the first time scientists have utilized this incredibly novel metric to identify illegal activities. In 2016 a team of scientists described how they used this same "bomb carbon" signature to accurately identify the age of ivory being shipped out of Africa. A ban on ivory sales in 1990 restricted trade of the material to ivory acquired before 1976. As atmospheric levels of carbon-14 have been consistently declining since open-air nuclear testing ceased in the 1960s, ivory samples can be accurately aged to within a few years by tracing those specific levels. That research startlingly discovered more than 90 percent of shipments seized between 2002 and 2014 were actually just a few years old and not antique ivory from pre-1976.

This new method of detecting forgeries is not without its limitations of course. It is estimated that atmospheric carbon-14 levels are rapidly returning to baseline pre-1950s levels. So this nuclear bomb peak signature will only be a useful detection metric for a few more decades, and even then it obviously only applies to forgeries produced after the 1940s and 1950s.

The new research was published in the journal PNAS.

Source: ETH Zurich