Laser diagnostics of painted artworks: Laser-induced breakdown spectroscopy in pigment identification

Laser-induced breakdown spectroscopy (LIES) was employed for the in situ analysis of pigments used in painting. LIES spectra were collected from a wide variety of pigments in powder form and in oil color test samples, Appropriate emission lines for the identification of the metallic elements in the pigments examined are proposed, Under optimal experimental parameters, the technique is minimally destructive; two pulses from a laser beam focused on the sample surface result in the formation of a small crater with typical diameter around 40 mu m and depth of no more than 10 mu m, Furthermore, recording LIBS spectra from successive laser pulses on the same spot of a model oil painting resulted in information regarding the pigment composition of several paint layers, showing the capability of the technique in performing depth profile analysis. Finally, a test case is presented in which an 18th century oil painting, subjected to partial restoration, was examined by LIBS, and the different pigments used in the original and in the restored part of the work were clearly identified. The results of our studies demonstrate the applicability of LIBS in the rapid, in situ, and practically nondestructive determination of pigments in painted artworks.