Higlights:• Reflection FTIR spectroscopy and OCT, when used together, enhance insight into the details of cleaning of easel paintings • FTIR complements OCT structural images by providing crucial information on the chemical composition of superficial layers • OCT complements the FTIR spectral data with information on the thicknesses of layers, both removed and left • This integrated approach increases the safety of the cleaning treatment.
AbstractAlthough the solvent removal of unwanted layers (e.g. aged varnishes, overpaints, oxalate patinas, dirt from easel paintings is one of the most frequently performed restoration treatments it is questioned regarding its controllability and safety to the artwork. There is thus a need for developing suited diagnostic methodologies able to inform restorers on the chemical, optical and morphological effects of cleaning. To this aim, we have explored the possibility of complementary use of Optical Coherent Tomography (OCT) and reflection FTIR. On the one hand, the OCT technique provides cross-sectional images with varnish layers visible and thus permits for measurement of their thicknesses. Combining many cross-sections into 3D data provides insight into the varnish thickness distribution over a given area of the paintings. On the other hand, reflection FTIR allows for a chemical characterization of the surface compounds revealing the nature of the varnish and monitoring its removal. Artificially aged model samples and two historical paintings were investigated at different steps of solvent cleaning tests and the results of the two techniques compared highlighting the benefits of their combined exploitation.
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