The Mona Lisa has given up another secret. Using X-rays to peer into the chemical structure of a tiny speck of the celebrated work of art, scientists have gained new insight into the techniques that Leonardo da Vinci used to paint his groundbreaking portrait. The research, published Wednesday in the Journal of the American Chemical Society, suggests that the famously inventive Italian Renaissance master may have been in a particularly experimental mood when he set to work on the Mona Lisa early in the 16th century. The oil-paint recipe da Vinci used as his base layer to prepare the panel of poplar wood appears to have been different for the Mona Lisa, with its own distinctive chemical signature, the team of scientists and art historians in France and Britain discovered.
"He was someone who loved to experiment, and each of his paintings is completely different technically," said Victor Gonzalez, the study's lead author and a chemist at France's top research body, the CNRS. "In this case, it's interesting to see that indeed there is a specific technique for the ground layer of Mona Lisa," he said in an interview with the AP. Specifically, the researchers found a rare compound, plumbonacrite, in da Vinci's first layer of paint. The discovery, Gonzalez said, confirmed for the first time what art historians had previously 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.
The paint fragment from the base layer of the Mona Lisa that was analyzed was barely visible to the naked eye, no larger than the diameter of a human hair, and came from the top right-hand edge of the painting. The scientists peered into its atomic structure using X-rays in a synchrotron, a 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 researchers to say with more certainty that da Vinci likely used the powder in his paint recipe.
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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." But the Mona Lisa and other works by da Vinci 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."
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