Mainly red and a hidden blue - Laboratory and MSI investigations on the Carolingian wall paintings in the Chapel of the Holy Cross of Mustair (Switzerland)

The Carolingian wall paintings on the upper floor in the Chapel of the Holy Cross were conserved from 2008 till 2016. In support of these measures and the investigations on the construction history, the interior decoration, renders, whitewashes and painting materials were analysed. Towards the end of the conservation work and in view of the future public display of the wall paintings to a larger public, the question was risen whether it would be possible to make the depictions more clearly visible by special photographic techniques, and if these photographic techniques could also help to transfer the laboratory results of a few individual samples to the surface area. This led to the investigation of selected areas of the wall paintings using multispectral imaging (MSI). In this paper, we report on the results of the laboratory analysis and of the scientific photography. It shows how the two methods have supplemented and supported each other during the investigation of the Chapel of the Holy Cross, how these results complemented the observations relevant to restoration and conservation, and how these observations enabled the interpretation of the scientific photography and laboratory results. Hence, we give an example that describes the potential of result-oriented interdisciplinary exchange. (C) 2019 Elsevier Masson SAS. All rights reserved.