Preliminary non-invasive study of Carolingian pigments in the churches of St. John at Müstair and St. Benedict at Malles

The monastery church of Müstair (Val Müstair, Switzerland) and the church of St. Benedict in Malles (Obervinschgau, Italy) contain painting cycles dating to the late eighth/early ninth century which are considered among the best preserved in Europe. Located inside a region of strategic importance at least since Roman times, during the medieval era both areas formed part of the diocese of Chur and were politically and culturally closely linked; the present border, in fact, developed in the course of the early modern period. The two painting cycles have been studied with a non-invasive approach using spectral multiband imaging, UV-visible diffuse reflectance spectrophotometry with fiber optics (FORS) and X-ray fluorescence spectrometry (XRF). The combined application of these techniques gave important insights into the painting techniques used in the two cycles. Clear similarities in the palette of pigments appeared; the colour palette included mainly materials typically used in medieval mural paintings, such as red and yellow ochres, carbon black, Bianco di San Giovanni and green earth, but lead pigments, such as red lead and massicot, which are less suited for use on plaster surfaces, were used as well. Of particular interest is the use of Egyptian blue and ultramarine blue that makes these paintings among the first in which the precious lapis lazuli pigment had been used in Europe. The occurrence of Egyptian blue and ultramarine blue puts the paintings closer to the ancient Roman than to the Romanesque tradition. A surprising result was the identification of As, which might indicate the use of orpiment for the creation of the wall paintings.