In each of his works, Leonardo da Vinci experimented not only with the composition techniques, but also with the materials used. To paint the Mona Lisa, one of his masterpieces, the artist likely used a unique lead oil mixture in the pre-coat. This is the conclusion a group of French scientists came to when they found plumbonacrite in a mini-fragment of the famous painting. The presence of this mineral, whose use in pictorial techniques was unusual at the time, suggests that the Renaissance genius once again tried to innovate by applying a thick mixture to the panel on which he depicted La Gioconda.
The study, published this Wednesday in the Journal of the American Chemical Society, “provides new information about Da Vinci’s palette,” explains Victor González, one of the study’s authors, a Frenchman of Asturian origin, in a telephone conversation. The results could be “useful for the understanding and preservation of his paintings,” says the researcher from the National Center for Scientific Research (CNRS, its French acronym). The European Synchrotron Radiation Laboratory (ESRF), the Louvre Museum and the French Ministry of Culture also took part in the study.
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Da Vinci, a great polymath who had the ability to combine art and science in the 16th century, left behind many manuscripts in which he developed his diverse interests, such as engineering and architecture. But as the study points out, “he left few clues about the materials used in his painting.” But the scientists agree on their willingness to experiment. In each of his paintings, the research adds, “the composition of the layers is different, as are the materials used.”
A small selection, but with a lot of information
The analyzed tiny fragment, which corresponds to the first layer applied by the artist to the famous poplar wood board, provides important information. It measures less than 100 micrometers – a micrometer is one thousandth of a millimeter – and was located on the upper right side of the painting that hundreds of people walk through every day at the Louvre Museum in Paris.
Scientist Marine Cotte at the European Synchrotron Radiation Laboratory (ESRF).STEF CANDE
To analyze this small sample, protected between two panes of glass, the team used the synchrotron in the city of Grenoble, a kind of giant microscope. They also used infrared analysis in the laboratory.
The results revealed the presence of a unique mixture of oil and lead that was very different from that normally observed in oil paintings of the period. “We unexpectedly discovered a compound called plumbonacrite,” says González. Da Vinci did not use it as a pigment and it was not part of his palette, the researcher emphasizes.
On the contrary, the substance was created as a result of chemical reactions in the paint itself, which suggests the presence of another compound. Researchers believe the other compound is lead oxide. In other words, to paint the first layer of the Mona Lisa, Da Vinci mixed his oil with lead oxide (litharge), a mixture that gave it a creamy, pasty consistency.
There are several indications for this hypothesis, explains Marine Cotte, co-author of the study and employee at the ESRF in Grenoble. In 2019, plumbonacrite was discovered in paintings by Rembrandt, the 17th-century Dutch master. In his case, he used it to make his canvases pasty, which emphasized the impression of chiaroscuro. “Rembrandt put us on the trail,” notes the researcher. “We thought it would be useful to re-analyze the colors we were working with to see if they also contained the same compound,” he explains.
“The Last Supper” and the manuscripts as clues
But what really provided further clues were the results of a parallel study conducted using samples of the Last Supper, the mural the artist created between 1495 and 1498 – before the Mona Lisa – in the refectory of the Santa María delle monastery. Grace from Milan.
Researcher Victor González at work. BRUNO LAVIT PHOTOGRAPHY
In addition to plumbonacrite, the researchers also found undissolved lead oxide particles in the samples. “It has to be said that we only analyzed a very small sample for the Mona Lisa. We would have found it anyway [óxido de plomo] in another sample,” explains Cotte.
To find more clues, the researchers decided to delve into the artist’s manuscripts available online. It wasn’t that easy. The words Da Vinci used are not the same as today. And painting terms are different from chemistry terms.
After a long search, they found a page from the Arundel Codex that mentioned lead oxide. [letargirio di piombo, en el manuscrito]. Only the context in which it was used was not that of painting, but that of pharmaceuticals. “We thought that if he used it as a medicine, he probably also used it for painting,” Cotte explains.
Apart from the fact that this hypothesis needs to be confirmed, many questions still remain unanswered. It is not known whether plumbonacrite is present throughout the canvas. But the study undoubtedly provides new elements for understanding the recipes used by Da Vinci and the evolution of his paintings over time.
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