The wall painting in Santa Maria Assunta Basilica crypt: new insight on non-invasive analytical techniques for the analyses of traditional pigments.

Abstract

Within the archaeological works in the summer of 2020, a series of wall paintings were uncovered in the Santa Maria Assunta Basilica in Torcello, including the crypt, where a blue backgrounded mural with multicolored figures on the apse and removed from the wall fragments that remained behind the altar were exposed. The preserved decoration shows 3 overlayed painting layers. A systematic cataloguing of the recovered fragments along with the use of non-invasive analytical techniques, hyperspectral imaging, Fiber Optic Reflectance Spectroscopy (FORS), Raman spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy enabled the characterization of the materials used for the creation of the painting layers. The hyperspectral imaging enabled the analysis of a higher number of fragments with minimum handling, and to reduce sampling as much as possible. The recording of the reflectance spectra by using FORS allowed the identification of certain pigments. Raman spectroscopy, as well as Fourier Transform Infrared (FTIR) spectroscopy techniques were used to identify the binders. All the information recovered from the techniques helped to identify the palette conformed mainly by earth pigments, its mineral composition, and the identification of the painting technique.