Scientists Detect Rare Chemical Compound in ‘Mona Lisa,’ Illuminating Leonardo’s Process

The Mona Lisa, one of the world’s most famous and most studied paintings, still has secrets to tell.

Scientists recently used X-rays to inspect the chemical structure of a speck of the painting, and the findings suggest that Leonardo da Vinci may have been experimenting with his style during its creation. 

Per research published Wednesday in the Journal of the American Chemical Society, the oil paint used by the Italian Renaissance artist in the base layer of the Mona Lisa has a chemical composition distinct from his other works—and even those made by his famous contemporaries. 

The presence of the rare chemical compound, named plumbonacrite, has confirmed a long-held theory among art historians that Leonardo utilized lead oxide powder to thicken and dry the paint layers of the Mona Lisa. 

“He was someone who loved to experiment, and each of his paintings is completely different technically,” Victor Gonzalez, the study’s lead author and a chemist at France’s CNRS, told the Associated Press. Scientists at CNRS, a prominent research body, partnered with art historians on the project. “In this case, it’s interesting to see that indeed there is a specific technique for the ground layer of Mona Lisa,” Gonzalez added.

The paper stresses how incredible it was to even detect the plumbonacrite, given its minuscule remnants: the speck of paint was nearly invisible to the naked eye and slimmer than a strand of hair. The scientists examined its atomic structure using X-rays produced by a synchrotron, a machine that accelerates charged particles through magnetics until they reach nearly light speed. 

While rare, this isn’t the first time plumbonacrite has been detected in the work of Old Masters. Gonzalez and his team have found a painting by Rembrandt, suggesting that the same, or very similar, paint recipes have been passed down through the centuries. 

“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.”