[MUSIC] Han Van Meegeren might be the most famous art forger of the 20th century.

He perfected the art of making fakes look really old, adding aging chemicals to his paints, even baking the finished piece and using a rolling pin to crack the paint.

He once tricked Nazi leaders into trading 137 priceless paintings for one forgery.

Han's forgeries are so well-known themselves that they're on display in Amsterdam's Rijksmuseum.

Bad fakes are easy to pick out, but how do you detect a world-class forgery from a world class artist?

Historians typically rely on their eyes and their knowledge, and they've been fooled many times.

But if you want to be the next master forger, you've got your work cut out for you.

There's new scientific tools that make it almost impossible to pass off a fine art fake, and one is thanks in part, oddly enough, to the nuclear arms race.

Beginning in the 1940s, we exploded over 550 nuclear bombs above ground, and this put huge amounts of two radioactive isotopes into the atmosphere.

These isotopes didn't exist on Earth before 1945, because they are only created by fission reactions.

Since then they've been sprinkled into the environment in miniscule amounts and show up everywhere from our bones and brains to pigments and painting supplies.

Any forgery made since 1945 will almost certainly contain a pinch of radioactivity from these isotopes.

Everything from old wine bottles to woodcarvings can be tested to tell if it was made after 1945.

But if someone forged a Leonardo way back in the 1800s?

We need a different trick.

Like carbon dating.

Carbon-14 is a heavier, radioactive isotope of carbon that's much rarer than ordinary carbon.

Things that eat air, like plants, and things that eat those things, have a fraction of this heavy carbon in their cells alongside all their normal carbon.

The radioactive carbon-14 is constantly decaying, but it's also being replenished as they eat.

But the moment something dies, the carbon-14 stops being replenished, and what's there slowly decays away.

By comparing the radioactive carbon to normal carbon, we can date the material.

Canvas, wood, even the oils used in paints are all plant-based and can be carbon dated.

This method proved that a Fernand Léger painting bought by collector Peggy Guggenheim was actually painted in 1959, four years after the artist's death.

What's under a painting can be just as informative as the art itself.

In the days before Amazon, canvases were hard to get, so artists often painted masterpieces on top of other paintings.

X-rays revealed Van Gogh's "Self Portrait with Glass" What?

You really want to say Van Goff?

Van Gocch?

Van Go!

Van Goff?

Van Go.

Whatever!

X-ray's revealed Van Gogh's "Self-Portrait With Glass" has a woman's entire portrait underneath, and Picasso's "Old Guitarist" was a re-used half-finished canvas.

A clever forger today knows - if you want to make a good fake, you have to paint over an old painting.

When "Portrait of a Woman", attributed to Goya, was x-rayed, it was shown to be a fake when a portrait by a completely different artist was found underneath.

So also make sure you're painting over something that matches.

If these other methods fail, the paint holds one more clue, like blood at a crime scene.

Paint has three main ingredients: pigment, for color; a binder, to hold the paint together; all dissolved in a solvent, like water or oil.

It's a chemical palette that's that ripe for forensics.

Since different different pigments were used in different different places over the different different centuries, they can give us an idea when and where a painting was made.

Zapping the paint with electromagnetic radiation and looking at the light it emits can tell us what elements are there.

These spectra are like a fingerprint for specific atoms.

They can tell if a red, for instance is from cinnabar or rust.

If there's one element that doesn't belong, the painting may be fake.

For most of history, white pigments contained toxic lead, which was later phased out in favor of other white pigments.

So when investigators examined this painting by Frans Hal and found white paint containing zinc, a pigment not invented until after Frans' death?

Forgery confirmed.

Only they didn't find out until after it sold for $10 million dollars.

But remember Han Van Meegeren?

He beat this atomic forensics by making his own authentic 1500s paints, with old pigments like cinnabar red and lead white.

So with all his tricks, how was he caught?

The chemicals formaldehyde he added, to harden and 'age' the paints?

It was too modern.

Even with authentic paint and canvas, and a master's touch, the one thing he couldn't do was make his paintings look the right kind of old.

There's just no substitute for time.

So the next time you're in a museum, look around and ask yourself how many forgeries you think are hiding there in plain sight, and how long until science sees the real picture?

Stay curious.