Leonardo Da Vinci’s paintings fascinate, partly due to a range of subtle optical effects that blur outlines, soften transitions and blend shadows like smoke. Known as “sfumato”, this technique is not only the result of the genius of the artist but also of technical innovations at the beginning of the 16th century. Minute observations, optical measurements and reconstitutions have already described the sfumato, but new analysis can confirm the procedure of this technique, especially related to how the gradation is done.
For the first time, Philippe Walter (LC2RMF) and his team, in collaboration with the ESRF and the Louvre Museum, have brought new insight on the sfumato thanks to a quantitative chemical study of the different painted layers. Seven paintings of Leonardo Da Vinci have been analysed without extraction, directly in the rooms of the Louvre Museum (Virgin of the Rocks, Mona Lisa, Saint John the Baptist, Annunciation, Bacchus, Belle Ferronnière, Saint Anne, the Virgin and the Child). The scientists concentrated on the study of the faces because they have the characteristics of the sfumato. They used a technique called
X-ray fluorescence(2) to determine the composition and thickness of each layer in nine faces (including Mona Lisa’s) painted by Da Vinci throughout 40 years of career.

Photo taken during the measurements on the Mona Lisa: X-ray fluorescence spectrometry was done directly on the paintings in the Louvre Museum. © V.A. Solé/ESRF

Representation of the superposition of layers in paintings in the face of Mona Lisa, on one light zone near the nose and the darker shadow of the hair. After treating the data, the thickness and concentration of pigments in the different layers. © C2RMF