REMOVAL OF VARNISH AND OVERPAINT LAYERS FROM EASEL PAINTINGS USING PULSED Nd:YAG LASERS

With the aim of finding less invasive and selective cleaning strategies for paintings restoration, this thesis provides novel insights and successful applications on the use of pulsed Nd:YAG lasers to safely remove aged varnish coatings and overpaint layers. The laser-material interaction under different irradiation conditions of several painting materials, such as terpenoid-based varnishes and oil paint layers, was extensively characterized using different analytical techniques. Laser ablation tests carried out on a large number of naturally and artificially aged varnish samples using the fifth (213 nm) and fourth (266 nm) harmonics of a QSwitch (15 ns) Nd:YAG laser evidence the fundamental importance of following a wavelength-based approach for the selective removal of painting varnishes. The promising results achieved on samples irradiated at 213 nm envisage very good prospects for the transfer of this laser cleaning approach in the field. Similarly, Long Q-Switching Nd:YAG (1064 nm) laser with a pulse duration of 120 ns was successfully tested for dealing the conservation problems of two female portraits dated around 1930 and 1910, respectively. The latter painting was found on the backside of a signed artwork by Giacomo Balla, one of the founding members of the Futurist Painters. These artworks were almost completely disguised by thick layers of oil overpaintings, which did not have any artistic relevance.Thorough characterization of the original pigments, binders, overpaintings and deterioration mechanisms allowed performing the complete restoration of the painting from Balla's studio, which returned an unknown Pre-Futurist artwork, and to plan that of the other female portrait by anonymous. At the same time, a systematic laboratory experimentation on prepared samples simulating the uncovering problems encountered in the real case has been carried out. This improved the knowledge of the laser induced-effects and ablation processes on different modern pigments and allowed to exploit such features for the selective removal of the undesired layers. The results reported disclose a significant application perspective for Nd:YAG laser ablation in conservation of modern easel paintings.