Nd:YAG vs Er:YAG : a comparative study of laser varnish removal on easel paintings (Conference Presentation)

The cleaning of paintings is carried out when an artwork legibility is jeopardized. This can be due to inevitable deposits on their surface or by a modification of the varnish optical properties as a result of ageing. For the most delicate restoration cases, laser processing was widely studied as an alternative to traditional techniques of painting cleaning. It encompasses two distinct approaches: the first one involves photo-thermal disaggregation of the unwanted material with an Er:YAG laser (2.94 μm) and eventually its chemical or mechanical removal while the second one involves ultraviolet laser ablation, generally with an excimer (193, 248 or 309 nm) or a high order harmonic Nd:YAG laser (213 or 266 nm). This study proposes a comparison of these two laserbased technique for removal of an urea-aldehyde resin, Laropal A81, widely used as a binder or varnish since the 90’s, but whose interaction with a pulsed laser was never studied. For this purpose, an Er:YAG laser (El.En LightBrush2 2.94 μm 500 mJ) and a 4th harmonic Nd:YAG laser (Quantel CFR 266 nm 50 mJ) were used. The cleaning procedure was monitored in both cases by optical microscopy, spectral domain-optical coherence tomography and UV-induced fluorescence. Results showed that both sources can give satisfying results when operated in optimal conditions.