A few micrograms of pictorial material, taken in 2007 from the preparatory layer of the Mona Lisa, have yielded valuable information about the processes used by Leonardo da Vinci.
The diffraction pattern recorded on the ID22 high-angle resolution line at the European Synchrotron Research Facility (Grenoble) and analyzed at the IRCP revealed the presence of nanoparticles of an unexpectedly rare compound, plumbonacrite Pb5(CO3)3(OH)2O. Simultaneous analysis of the white lead pigment present, infrared spectroscopy and study of the Italian master’s writings showed that Leonardo had dissolved a significant quantity of lead oxide PbO, a compound he frequently mentioned, in the oil to make the paint more viscous, probably to compensate for the roughness of the wood panel on which he later painted the Mona Lisa. Nevertheless, this basic additive altered the composition of the lead white by attacking its acid component PbCO3, resulting in the neoformation of plumbonacrite. This original process, which seems to have been rediscovered only a century later by Rembrandt, confirms if proof were needed that Leonardo knew how to put his scientific talents at the service of his art.
This work, carried out by researchers at C2RMF and IRCP, has been published here.