A combined use of FORS, XRF and Raman spectroscopy in the study of mural paintings in the Aosta Valley (Italy)

Mural paintings which decorate the external façade and the internal apsidal wall of a chapel dedicated to St. Maxime and located at Challand St. Victor in the Aosta Valley (Italy) have been analysed with a combined approach involving high-resolution fibre-optic reflectance spectroscopy (FORS), X-ray fluorescence (XRF) spectrometry and Raman spectroscopy. The paintings are attributed to Giacomino from Ivrea, a painter active around the midfifteenth century. In order to characterise the palette used by the painter and to yield information useful to restorers, the cited techniques were used either in situ with portable instruments and in laboratory, working on micro samples withdrawn from paintings. The global analytical approach, though not entirely non-invasive, can indeed be considered non-destructive as multiple analyses, including SEM-EDX, could be carried out on the micro samples, exploiting the features of each technique. On the basis of the information obtained, the palette was found to be composed of typical fresco pigments such as calcite, azurite, malachite, vermilion, red and yellow ochres. A particular situation was noted for black pigments since the presence of graphite, rather than wood or lamp carbon, was found, possibly related to the presence of graphite deposits in the Aosta Valley. Furthermore, the presence of smalt superimposed to azurite in areas showing evidence of repainting was detected, suggesting that paintings were subjected to retouching at a relatively early stage after the original execution. Finally, the presence of tin foils, used to decorate haloes of Evangelists, was ascertained.