Another mystery of the Mona Lisa has been solved: it’s not about her smile

“Mona Lisa” has revealed another of its secrets. Scientists have used X-rays to study the chemical structure of Leonardo da Vinci’s famous painting. They learned what techniques a Renaissance artist used to create a portrait of a woman smiling.

The study was published Oct. 11 in the Journal of the American Chemical Society. Its authors suggest that the famous Italian Renaissance master was in search of new artistic methods while working on the Mona Lisa. Therefore, the picture was painted using an experimental method. The study also involved the European Synchrotron Radiation Laboratory ESRF, the Louvre Museum and the French Ministry of Culture.

“In this case, it’s interesting to see that there really is a specific technique for applying the first layer of the Mona Lisa,” Victor Gonzalez, lead author of the study and a chemist at the French research center, told The Associated Press.

As a group of scientists and art historians from France and Great Britain discovered, the recipe for oil paint that Da Vinci used to process the wooden base for the painting was different from the subsequent layers of the Mona Lisa.

Many paintings from the early 1500s, including the Mona Lisa, were painted on wooden boards, which required a thick undercoat to be laid down before work could begin. Scientists discovered that while other artists commonly used plaster, da Vinci experimented.

As it became clear, the first layer has its own distinctive chemical signature. As the study highlights, the artist “left few clues about the materials used in his painting.”

“He loved to experiment, and each of his paintings is technically completely different,” Victor Gonzalez said. The scientist studied the chemical composition of dozens of works by Leonardo da Vinci, Rembrandt and other artists.

As mentioned above, the first layer has its own chemical composition. In particular, scientists discovered a rare compound in it – plumbonacrite. This discovery, according to Gonzalez, confirmed the hypothesis of art historians for the first time. They had previously suggested that Leonardo used lead oxide powder to thicken and help dry the paint when he began working on the portrait now visible behind protective glass in the Louvre Museum in Paris.

Plumbonacrite was also used by other painters. For example, the Dutch artist Rembrandt in the 17th century. Gonzalez and other researchers had also previously found plumbonacrite in his work.

“Plumbonacrite is truly the secret ingredient in his recipe. This is the first time we can chemically confirm this. This discovery also tells us that recipes have been passed down for centuries. It was a very good recipe,” notes Gonzalez.

This rare mineral is believed to be the key to the secret of long-lasting paint. Now it is used in the automotive industry: to fix red and orange shades.

Scientists think da Vinci’s recipe was as follows: he dissolved orange lead oxide powder in flaxseed or nut oil and heated the mixture to create a thicker, faster-drying paint.

“You will get a very nice golden color of oil. It’s more like honey,” Gonzalez commented on the discovery.

Italian art specialist and curator at New York’s Metropolitan Museum of Art Carmen Bambach called the study “very interesting” and said that any scientifically verified new understanding of Leonardo da Vinci’s painting technique is “extremely important news for the art world and our broader global society.” The expert also called the discovery of plumbonacrite in the Mona Lisa evidence of “Leonardo’s spirit of passionate and constant experimentation as an artist – this is what makes him timeless and modern.”

Studying the fragment, scientists thoroughly checked its atomic structure. To do this, they used X-rays in a synchrotron, a machine that accelerates particles to the speed of light and similar to a giant microscope in Grenoble. In the laboratory, they also used infrared analysis, according to El País.

This principle of parsing atoms allows one to unravel the chemical composition of any speck: “A microsample from the soil layer of da Vinci’s Mona Lisa was analyzed using high-angular resolution synchrotron X-ray diffraction and Fourier transform infrared spectroscopy,” they explained in the paper.

The US Sun notes that the sample taken for this experiment will not spoil the picture. It was so small that it was no larger than the width of a human hair. The researchers carefully took a sample from the upper right corner of the painting, which is impossible to see with the naked eye.

“We faced the additional challenge that there is very little scientific analysis of the Mona Lisa and da Vinci’s paintings in general, so it was difficult to compare our results with previous studies,” explains ESRF scientist and co-author Marine Kott.

This is just one of the secrets of the Mona Lisa, a mysterious woman that the Louvre says is a portrait of the wife of a Florentine silk merchant, Lisa Gherardini. But researchers turn their attention not only to the Mona Lisa, but also to other works by Leonardo da Vinci, which also keep other secrets: “Of course, there is much, much more that can be discovered. We’re barely scratching the surface. What we are saying is just another building block of knowledge,” Gonzalez said.