X-rays reveal new secret about the ‘Mona Lisa’ – showing Leonardo da Vinci’s experimental mood when he painted the 16th-century masterpiece

Leonardo da Vinci painted his famous ‘Mona Lisa’ with an experimental ‘honey gold’ base-coat, according to new X-ray analysis by chemists in Britain and France. 

The researchers used a technique called ‘synchrotron X-ray diffraction’ to peer into the molecular structure of a tiny speck of da Vinci’s celebrated work of art.

What they found was a distinct chemical signature under the surface that appears to have been new for his ‘Mona Lisa’ — a base paint which they believe da Vinci crafted with an orange-hued lead oxide powder and possibly linseed or walnut oil.

The innovation, now called ‘plumbonacrite,’ was later adopted by 17th century Dutch Masters and is used by automakers as a color preservative today, to keep red and orange sports cars looking bright.

‘He was someone who loved to experiment,’ said the new study’s lead author. ‘Each of his paintings is completely different technically.’

The ‘Mona Lisa,’ da Vinci’s groundbreaking portrait of the woman with the enigmatic smile, these scientists and art historians argue, still has more secrets left to reveal.

Using X-rays to peer into the chemical structure of a tiny speck of Leonardo da Vinci’s celebrated work of art, the ‘Mona Lisa,’ scientists have gained new insight into a rare paint used in his groundbreaking portrait. Above, da Vinci’s Mona Lisa in the Louvre museum

Around 7.5 million visitors flock to Paris to visit the Louvre ever year, by some estimates, meaning around 30,000 people a day visit the ‘Mona Lisa,’ including TikTok influencers eager to snap their best selfie with da Vinci’s 16th century masterpiece

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‘It’s interesting to see that indeed there is a specific technique for the ground layer of ‘Mona Lisa,” lead author Victor Gonzalez, a chemist at France’s top research body, the Centre national de la recherche scientifique (CNRS), told the Associated Press.

The rare compound, plumbonacrite, was discovered on da Vinci’s first layer just above the poplar wood upon which the Italian Renaissance icon painted his masterpiece.

The discovery, according to Gonzalez, confirmed for the first time what art historians had long only hypothesized: that da Vinci most likely used lead oxide powder to thicken and help dry his paint as he began working on the portrait that now stares out from behind protective glass in the Louvre Museum in Paris.

(In May 2022, the famous work was attacked with a custard pie by climate activists.)

The chemists’ new analysis suggests that the famously curious, learned and inventive Renaissance master da Vinci may have been in an experimental mood when he set to work on the ‘Mona Lisa’ early in the 16th century

Gonzalez has studied the chemical compositions of dozens of works by da Vinci, as well as the Dutch painter Rembrandt and other artists.

READ MORE: The most audacious art heists in history: From Mona Lisa stolen by worker who simply lifted it off the wall to theft of an Edvard Munch by crooks who left note saying: ‘Thank you for the poor security’

His team’s research was published Wednesday in the Journal of the American Chemical Society.

Their work suggests that the famously curious, learned and inventive Renaissance master may have been in a particularly experimental mood when he set to work on the ‘Mona Lisa’ early in the 16th century.

Carmen Bambach, a curator and specialist in Italian art at New York’s Metropolitan Museum of Art, while not involved in the study, called the research ‘very exciting.’

Any scientifically proven new insights into Leonardo’s painting techniques, Bambach said, are ‘extremely important news for the art world and our larger global society.’

Finding plumbonacrite in the ‘Mona Lisa’ attests ‘to Leonardo´s spirit of passionate and constant experimentation as a painter,’ Bambach told reporters.

‘It is what renders him timeless and modern.’

Around 7.5 million visitors flock to Paris to visit the Louvre ever year, by some estimates, meaning that around 30,000 people a day visit the ‘Mona Lisa,’ including TikTok influencers eager to snap their best selfie with the 16th century masterpiece.

But this paint fragment from the base layer of the ‘Mona Lisa,’ which Gonzalez analyzed, was barely visible to the naked eye — no larger than the diameter of a human hair.

His team’s chemical sample came from the top right-hand edge of the painting.

The scientists peered into its atomic structure using X-rays in a synchrotron, a large machine that accelerates particles to almost the speed of light. That allowed them to unravel the speck’s chemical make-up.

Plumbonacrite is a byproduct of lead oxide, allowing the researchers to say with more certainty that Leonardo likely used the powder in his paint recipe.

‘Plumbonacrite is really a fingerprint of his recipe,’ Gonzalez said. ‘It’s the first time we can actually chemically confirm it.’

Above, the Mona Lisa as it can be seen today in 2023 at the Louvre in Paris

After Leonardo, Dutch master Rembrandt may have used a similar recipe when he was painting in the 17th century; Gonzalez and other researchers have previously found plumbonacrite in his work, too.

‘It tells us also that those recipes were passed on for centuries,’ Gonzalez said. ‘It was a very good recipe.’

Leonardo is thought to have dissolved lead oxide powder, which has an orange color, in linseed or walnut oil by heating the mixture to make a thicker, faster-drying paste.

‘What you will obtain is an oil that has a very nice golden color,’ Gonzalez said. ‘It flows more like honey.’

But the ‘Mona Lisa’ — said by the Louvre to be a portrait of Lisa Gherardini, the wife of a Florentine silk merchant — and other works by Leonardo still have other secrets to tell.

‘There are plenty, plenty more things to discover, for sure. We are barely scratching the surface,’ Gonzalez said. ‘What we are saying is just a little brick more in the knowledge.’