Optical and spectroscopic tools for evaluating Er:YAG laser removal of shellac varnish

Publication Type:

Journal Article

Authors:

Jana Striova; Barbara Salvadori; Raffaella Fontana; Antonio Sansonetti; Marco Barucci; Enrico Pampaloni; Eleonora Marconi; Luca Pezzati; Maria Perla Colombini;

Source:

Studies in Conservation, Volume 60, Number S1, p.S91-S96 (2015)

Abstract:

We report on tests to remove naturally and artificially aged shellac varnish by laser and traditional chemical cleaning from the substrates of mural paintings. Optical tools were used for the evaluation of cleaning processes, in particular laser microprofilometry to assess the changes in the surface morphology and time-domain confocal optical coherence tomography (OCT) to evaluate varnish thickness. The cleaning assessment was integrated with molecular characterization provided by portable Fourier transform infrared spectroscopy operating in reflectance mode, and colorimetric measurements. This complete analytical approach led to optimized laser-based cleaning tests at 1.9 and 2.6 J/cm2 in the presence of isopropanol, which ensured controllable and safe partial removal of shellac varnish without alteration to the substrate morphology.