AN UNUSUAL WHITE PIGMENT IN LA VERNA SANCTUARY FRESCOES: AN ANALYSIS WITH MICRO-RAMAN, FTIR, XRD AND UV-VIS-NIR FORS

The fresco cycle in the Corridoio delle Stimmate at the La Verna Sanctuary (Arezzo) was painted by Baccio Maria Bacci (Florence, 1888-1974) in two phases: in the 1930s and the 1950s-60s. In the second phase he depicted some new scenes and restored others from the first phase, which were heavily damaged during World War II. A recent discovery of a box containing his pictorial materials gave an opportunity to study the original materials used by the artist in the 1950s-60s. Among several powdered pigments only one white powder was found. It was initially assessed through bulk analysis using ultraviolet (UV), visible(Vis), and near infrared (NIR) Fibre Optic Reflectance Spectroscopy (FORS) and X-ray Diffraction (XRD). The obtained data showed that its main constituents were zinc white (ZnO) and lithopone (ZnS·BaSO4). Further microscopic analyses were conducted by using Scanning Electron Microscopy/Energy Dispersive X-ray analysis (SEM-EDX), Fourier Transform Infrared Spectroscopy (FTIR), and micro Raman techniques, but some of these results were not consistent with bulk analysis, highlighting the limitations sometimes encountered when using only bulk or micro analytical techniques.