Practical application of visible-induced luminescence and use of parasitic IR reflectance as relative spatial reference in Egyptian artifacts

Abstract

Egyptian blue (CaCuSi4O10) is one of the most ancient artificial pigments, widely used in ancient times. Its peculiarity is an exceptional infrared emission upon visible excitation, allowing an easy and non-invasive diagnostic through the so-called visible-induced luminescence (VIL) technique. Usually, it requires total absence of infrared parasitic light, highlighting areas in which the pigment is present even in traces. In this report, we propose the introduction of a small portion of IR parasitic light as spatial reference for locating Egyptian blue on analyzed object. In VIL modality, the contemporary reflectance transformation imaging (RTI) and 3D photogrammetric model reconstruction were performed with the final 3D rebuilding of surface, morphology, and pigment distribution. We demonstrated the possibility to perform VIL and 3D photogrammetry without opening the conservation case that is extremely important by a conservation point of view, avoiding any microclimatic alteration, compatibly with the minimum invasiveness (absence of contact and displacement of the object).