1. Introduction

After the first scientific examinations carried out on the Mona Lisa in the early 1950s, Madeleine Hours concluded, given the subtlety of the effects obtained: "Her technique defies all forms of analysis".

Leonardo da Vinci blurs contours, softens transitions and melts shadows "like smoke". It is from this term, fumo in Italian, that the word sfumato today associated with his technique is derived: a vaporous effect, "without lines or contours, like smoke". These effects were achieved thanks to the genius and skill of Leonardo da Vinci, but also to technical innovations in a period of artistic effervescence. At the time, many artists were looking for new techniques to improve the visual and conservation properties of their works. The technique of glazing emerged from this research: the superimposition of these thin, translucent layers of paint creates effects of...