Leonardo da Vinci not only invented futuristic machines, he also innovated in painting. A chemical analysis of The Mona Lisa and of The Lord’s Supper carried out using a particle accelerator reveals that this great genius was also experimenting with new pictorial techniques.
Researchers from the National Center for Scientific Research (CNRS), the Center for Research and Restoration of the Museums of France and the Louvre Museum were particularly interested in the layer of white preparation that was applied to the wooden panel and on which the artist applied his colors.
For their study, they used a micro-sample of The Mona Lisa which had been taken in 2007 – in the upper right area of the painting which is normally hidden by the frame – which they subjected to high intensity X-rays from the European Synchrotron in Grenoble. “The synchrotron is a particle accelerator, a sort of giant microscope, which allows us to probe matter at very small scales,” explains Victor Gonzalez, art chemist at the Laboratory of Supramolecular and Macromolecular Photophysics and Photochemistry, in a telephone interview. of the CNRS / ENS Paris-Saclay.
“This irradiation gave us information on the chemistry of the materials that make up this fragment. It was thus observed that in the preparation layer of The Mona Lisa [peinte de 1503 à 1519], there was a somewhat surprising compound: leadonacrite. This unexpected compound was a clue that allowed us to determine the recipe that Leonardo would have used for his first support layer. »
In fact, leadonacrite was not applied by Leonardo da Vinci. It was formed in situ in the painting, specifies the chemist. “The fact that it can only exist under certain particular chemical conditions has informed us about the recipe used by Leonardo. This recipe consists of mixing linseed oil with lead oxide (also called litharge), to which lead white is then added. [une mixture de deux carbonates de plomb]. »
Lead white was used since ancient Egyptian times and was used until the beginning of the 20th century.e century. But what is “innovative is this preparation of oil with lead oxide”. “There is evidence that Leonardo used this recipe which was not common in Italian Renaissance technique. We see that Leonardo is experimenting, because he did not apply this recipe in these other paintings. And this is very important for our understanding of the techniques and palette of this painter,” emphasizes Mr. Gonzalez.
Preparation layer
All the paintings he painted from 1485 to 1490 indeed have a different layer of preparation, the researchers say in the article they published about their discovery in the Journal of the American Chemical Society (JACS).
The analysis of 17 samples of The Lord’s Supper painted between 1494 and 1498 on a wall of the convent of Santa Maria delle Grazie, in Milan, also revealed the presence of leadonacrite. Which confirms that Leonardo used the same recipe as for The Mona Lisa.
In the case of The Lord’s Supper, it is a real innovation compared to the traditional fresco technique. “Leonardo painted on the wall as if he were painting a picture. Normally, we don’t do that, we don’t paint with oil for a fresco,” Mr. Gonzalez points out.
“The fresco technique [dans laquelle le liant n’est pas de l’huile, mais de l’eau] is completely different from the technique of oil painting on wooden panel at that time. But the process that Leonardo used allowed him to paint with much more finesse, because oil allows you to be very fine, it allows very particular renderings. However, it was not a good idea to paint with oil on a wall. It is for this reason that The Lord’s Supper is in very poor condition today. The conservation is catastrophic because he used a technique that was not suitable,” explains the specialist in the chemistry of works of art.
But why did you add lead oxide to the oil? Adding lead oxide to the oil causes it to dry faster and not have the same consistency. “Oil from the supermarket is fluid, if you cook the oil with lead oxide, it will become more pasty like honey, and it will dry more quickly. We hypothesize that Leonardo wanted to have a preparation layer which dried quickly, which had a certain behavior, which allowed him to spread the paint with more flexibility, which allowed a better artistic rendering, and that is why that he used this process,” says Mr. Gonzalez.
“However, it is difficult to say whether this technique had an effect on the rendering of the painting as a whole,” he concedes.