Combination of Optical Coherence Tomography and SANS for the study of cultural heritage

The beamtime requested is aimed at deepening the knowledge of an open challenge in painting conservation, named blanching. When stored in a high-humidity environment or exposed to water, paintings coated with a transparent varnish layer undergo whitening. We observed that this damage is reversible if the water contact is limited in time. We aim to investigate the nano-structural changes happening in the polymeric varnish layer during water uptake for both short (reversible blanching) and long (irreversible blanching) water contact. We are developing a unique non-invasive capability to simultaneously monitor structural changes at both nano and micro scales by combining SANS and a bespoke Optical Coherence Tomography (OCT). SANS will provide time-resolved spectra on the growth of the nanopores, and OCT will map out the depth profiles of samples, allowing for swelling monitoring. The combined approach will show the correlation between pore changes and film growth, pointing out the time scale at which the two processes take place, clarifying how irreversible damage becomes visible. We build on preliminary work, where we have demonstrated that blanching is observable in SANS, quantifying the water uptake and the pore growth during D2O infiltration, showing structural changes that continue over weeks. In this proposal, we aim, through a series of OCT-SANS measurements, focusing on reversible and irreversible processes, to provide a comprehensive view of varnish blanching.