Non-invasive study of Early Medieval wall paintings in the churches of St. Stephan in Chur and St. Martin in Disentis (Switzerland)

The Early Medieval wall paintings preserved in historical sites of the ancient Raetia Curiensis region (today’s Swiss Canton of Grisons and parts of Northern Italy and Austria) provide a rare testimony of the art of this period. This contribution presents the results of the non-invasive scientific campaigns carried out in the churches of St. Stephan in Chur and St. Martin in Disentis/Mustér (Canton of Grisons, Switzerland). In the church of St. Stephan, the investigations were performed in-situ on the surviving wall paintings of the crypt and on several painted plaster fragments (crypt and upper church), while in Disentis a selection of painted stucco fragments was studied. All the painted surfaces were firstly examined with technical photography in visible, infrared, and ultraviolet ranges, followed by portable spectroscopic point analyses (i.e. HH-XRF, FORS, and FTIR). The findings revealed the composition of most pigments such as iron-based pigments (yellow and red ochres, green earth) and lead-based pigments (i.e., lead white and red lead). In addition, for the St. Stephan’s site, the Visible Induced IR Luminescence (VIL) images combined with point analyses, allowed for the identification of Egyptian blue (EB). Furthermore, the presence of zinc in the wall paintings of the crypt of St. Stephan and the absence of this element in those referable to the upper church, suggested differences in the procurement of copper for the manufacture of EB. The presence of arsenic and lead in iron-bearing pigments detected in the wall paintings of the crypt and their negligible amount in those of the upper church, suggested that these pigments come from a different sourcing area. In the church of St. Martin, the use of different pigments for the execution of the incarnate of the figures, the extraordinary state of conservation of minium, and the absence of green and blue pigments are remarkable features of the stucco decoration paintings.