In the late 1960s, prominent  art collector Peggy Guggenheim purchased a painting by Fernand Léger.

Léger was one of the most  important Cubist artists, and this painting was part of his landmark series from the 1910s called Contraste de formes. Guggenheim bought the painting  from a reputable gallery, and all its paperwork seemed to be in order: Its line of ownership was well documented for the previous 15 years or so.

She planned to add the piece to  her already impressive Cubism collection, including some works  she had bought from Léger himself. But several years after the painting’s purchase, an art historian expressed  doubt about its authenticity. This historian specialized in Cubism,  and Léger had personally given pieces of art to him.

So the guy  knew what he was talking about. But for 40 years, no one  could definitively confirm the painting’s authenticity  or prove it was a fake. The canvas was put into storage,  where it languished until 2013.

That’s when an unlikely team of  detectives decided to try something no one had ever used in solving an  art forgery case: nuclear bombs. [♪INTRO] Museums have an impressive toolbox of methods for busting art forgeries. The first line of defense is usually  the painting’s provenance and style. A curator examines provenance by  tracing the line of ownership, ideally all the way back to the artist themself.

Gaps in ownership, or  unverified links in the chain, might indicate that some  funny business took place. Has anyone else read The Goldfinch? A talented historian will also  consider a painting’s style.

The composition, brushstrokes, colors— and even sometimes the way an artist tends to paint ears or something— can be compared to other paintings by the artist. In the case of the Léger painting, both the provenance and style were questionable. There was a long gap between  the painting’s supposed creation date and the beginning of its paperwork.

And it had been relegated to storage precisely because of a historian’s  doubts concerning the style. The next layer of investigation takes an even closer look with microscopy. As a painting ages, the paint itself cracks.

And sometimes, forgers just  draw on these crack lines! Zooming in with a microscope,  or even just a magnifying glass, can quickly unmask these deceptions. But this method has the most  potential for very old paintings, when the layers of paint have  had plenty of time to age.

For a relatively young painting, like the Léger, optical examination often doesn’t  turn up conclusive results. A more useful method for the  Léger canvas was x-ray imaging Scientists can use x-rays to determine the pigments used in each color of paint. In this case, researchers looked at the painting in question and a verified work by Léger.

They noticed that the colors in each painting had different chemical formulas. What’s more, the pigments in  the questionable painting seemed to come from organic sources,  like plants and animals. While the confirmed painting used synthetic pigments made from designer minerals.

Which is weird, but it isn’t totally  out of the question that Léger might have just been trying  a different brand of paints. As a last ditch effort, scientists  can perform mass spectrometry. This method requires a sample  of the paint or the canvas, but the catch is that the sample  will be completely vaporized.

The vapor can then be separated into individual molecules to tell you exactly  what it was made from. This is most useful for studying the stuff that holds the paint together, called a binder. For oil paints that’s, well,  oil that typically comes from a plant like linseed, poppy, or walnut.

But newer paints might have fancier binding chemicals to make them dry faster or crack less. So if you do mass spectrometry and  find paint binders that wouldn’t have existed when the painting  was supposedly created… well then you’ve caught yourself a fake. The main problem with mass  spectrometry is that it’s destructive and requires removing a  chunk of the paint or canvas.

If you’re having trouble  getting conclusive results from non-destructive methods,  then it’s a huge risk to remove any part of a  potentially-authentic painting. The x-rays had turned up questionable  results in the Léger, but nothing to suggest the painting was created  during the wrong time period. And given the invasiveness of removing a paint sample for mass spectrometry… it isn’t surprising that they opted not to try it.

So the painting sat … for 40  years. And for a long time, it probably looked like it was  going to be one of the many artworks that get permanently tucked away because no one knows for sure if they’re legit. But in 2013, a team of nuclear physicists decided to take a crack at solving the mystery.

They were going to try carbon dating. Before I tell you more about  what they learned, a quick ad. This SciShow video is supported by Brilliant: an online learning platform that helps you build knowledge at your own pace.

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Carbon dating involves counting the number radioactive carbon-14 atoms  that exist in a sample. Carbon-14 is naturally created when cosmic rays interact with our atmosphere. We know how often those interactions occur, so we can reliably predict—and measure— how much carbon-14 exists in nature.

Because it’s radioactive, carbon-14 decays into nitrogen-14 with a half-life of about 5700 years. So however much carbon-14 you started with, in 5700 years you’ll only  have half that amount and in another 5700 years it’ll get cut  in half again, so on and so forth. Based on how much carbon-14 is in a sample, you can tell how long the  carbon-14 has been decaying, and you can determine roughly  how old the object is.

I can hear you saying: “Hold on,  if the half-life of carbon-14 is more than 5000 years, can’t it  only be used for super old stuff? How does this help with a  painting from the 1910s?” And you’re RIGHT! That’s usually the case.

But everything changed in the 1950s and 60s, thanks to the testing of nuclear bombs. The Atomic Age was marked by  extensive nuclear detonations. The first above ground nuclear test  happened in 1945 in New Mexico, which you might have learned about  during the Barbenheimer summer.

But testing expanded and accelerated in the following decades as the Cold War ramped up. Those tests shot radioactive  byproducts high into the atmosphere, including carbon-14, and the fallout  drifted across the entire globe. Enough carbon-14 was generated  by nuclear detonations that the atmospheric concentration  of carbon-14 quickly doubled.

The fallout was so extensive and concerning that most nuclear testing was banned in 1963. But all that carbon-14 had to go somewhere… it won't decay for thousands of years. In the meantime, it has gotten into  the cells of every living thing, since we build our bodies from  carbon in the environment.

Plants draw carbon from the air,  and for every trillion carbon-12 atoms they absorb, they’ll also  pick up one or two carbon-14 atoms. Animals… including humans… eat those plants and repurpose the carbon  throughout our entire bodies. From the moment you start living  until the moment you stop, you’re picking up carbon-14.

You have a carbon-14 signature. Your cat has a carbon-14 signature. And the seeds that are harvested to create oil paint binder have a carbon-14 signature!

As do the plant fibers that are  eventually woven into canvases. Carbon dating used to require  several grams of material, but can now be conducted with  as little as a few milligrams! The sample is vaporized and mass spectrometry is used to count the ratio of  carbon-14 to carbon-12 atoms.

With just a tiny sample you can pin down the date of an object to within a 1-3 year window. See, all that nuclear testing  created a characteristic spike in the concentration of atmospheric carbon-14. The spike starts in the  1950s and drops every year as the carbon-14 in the air makes  its way into organic matter.

Because the graph changes so  rapidly from one year to the next, it’s possible to precisely  match the date of an object to the concentration levels in the graph. So by using just a couple threads of canvas, the physicists were able to perform carbon dating on the Léger painting. The canvas contained a relatively  enormous amount of carbon-14: 1.29 parts per trillion.

That might not sound super  drastic, but it’s far too much for the canvas to have been created in the 1910s! The material for the canvas  was definitely harvested after the “bomb peak”, made with  plants from either 1959 or 1962. And considering Léger died in 1955… things don’t add up either way.

The painting was undeniably a fraud. Since the Léger case, other forgeries have been uncovered using carbon dating. Including one where an old canvas had been painted over with historically accurate paint pigments.

But even with these painstakingly  detailed replications, the oil paint binder from recently grown  crops was a dead giveaway. We’re now back to pre-nuclear concentrations of atmospheric carbon-14. So you might think forgers  would be back in business.

But scientists predict that  by the end of this century, we’ll actually drop below the  pre-nuclear concentrations. This is because we’ve been burning a LOT of fossil fuels and adding their carbon to the air. Fossil fuels are so old that they have almost no carbon-14 left in them at all!

So the atmospheric carbon-14  is actually being diluted, and will eventually extend the “bomb  peak” curve into negative ranges, rather than bottoming out at natural levels. Future forgeries might run into the problem of not having enough carbon-14 to be convincing fakes. It’s fascinating to know that every living thing carries a carbon-14 signature within them.

We can tell exactly when something  started and stopped “living”. You can be carbon dated, Peggy  Guggenheim could be carbon dated, and the forgers themselves.  Even things we don’t usually think of as “alive”, like  paintings, can be carbon dated. It’s one of those things you just can’t fake.

You either have it or you don’t! So if you’re a budding forger, maybe apply your artistic skills to original works, and avoid doing any art crimes  for the foreseeable future. [♪OUTRO]