For Leonardo, shadows are a basic component of painting. On them, in fact, depends the effect of relief. He conducts a series of innovative experiments to determine their nature, size, shape and intensity.
Starting from the complex geometries of shadows, Leonardo's research extends to analyzing colors and the phenomena of their reflections. Falling within this sphere of research are his refined considerations on "sfumato".
The characteristic perhaps most greatly admired in Leonardo’s works is the refined sfumato of the flesh tones. Through the technique of sfumato, the transition between light and shadow in the subjects portrayed is realized by exceptionally delicate gradation. Based on the research carried out by Jacques Franck a convincing hypothesis has been formulated, which is compatible with the material evidence of the Mona Lisa as analysed by the Louvre’s laboratory, on the method employed by Leonardo to achieve these effects: the micro-division of tones, a procedure described in detail for the first time here.