What does the Mona Lisa really look like? Analysis of works of art down to the nanometer scale

The material analysis of works of art aims to better understand the techniques of the ancient cultures and to preserve the cultural heritage for future generations. The analysis brings to light new and unique information for authentification, for conservation and to better understand the history of artistic techniques. Until now, the methods were intensively developed and adapted to the specific, precious character of the works of art.
Works of art are examined from the macro, to the micro, down to the nano scale, thanks to transmission electron microscopy (TEM), atomic force microscopy (AFM), ion beam techniques, or synchrotron radiation spectometries.
The laboratory of the C2RMF inside the Louvre analyzed Leonardo's famous painting to provide the best conditions for its installation in the new glass case and with the aim to understand in depth the master's secret know-how. Thirty-nine specialists undertook a comprehensive and pluridisciplinary study following a materials approach using non-invasive techniques.
The panel on which Mona Lisa is painted is a single plank of poplar wood, typical of Italian production from the second half of the 13th C. The careful examination reveals a transversal cut, close to the trunk's core. The split in the panel was evident long ago and the present study proves its complete stability over time, as the split is probably contemporaneous of Leonardo himself.
The aim of the scientific examination was to look at the work in a new way, helped by the chemical analyses. The painting was realized through the superposition of several layers of hybrid materials, mixture of pigments and binding agents. Photographs in grazing light, with IR, UV flourescence, X-ray put together, permit a careful reading of the image and evidence the process of creation.
Leonardo's palette was evidenced by the analysis of the paint layer undertaken by XRF, Raman spectrometry and spectrophotometry. An optical characterization of the transition (sfumato) reveals that it produced an optical effect similar to that created by the glazes in the Renaissance Flemish paintings. Finally, the relationship between colors could not depend solely on their juxtaposition, but also on a specific connection between two colors, such as those of the flesh tints and hair, with subtleties of transistion (sfumato) that were intended by the artist.