A new methodology for incorporating weathering products into analyses of prehistoric pictorial matter: A case study at the Rocher Du Château schematic rock art site

Comparisons of prehistoric pictorial matter and colouring matter can provide information about the chronology of rock art and the provenience of the materials used. However, characterizing pictorial matter is difficult because samples generally contain fragments of substrate and overlying weathering products, as well as pictorial matter. Studies of pictorial matter have long taken account of the substrate, but attempts to isolate weathering products are much more recent. The current article describes a methodology for doing this and its application to the Rocher du Château schematic rock art site. This site in Savoie, France, is one of only a few such sites whose archaeological layers contain colouring matter (possibly dated to 4,600 – 4,000 BC) that is potentially the same as the rock art pictorial matter and close to a potential source of colouring matter. Our aim was to ascertain whether the archaeological colouring matter was related to the rock art pictorial matter and to identify its source. Results showed that the phosphorus in the Rocher du Château’s paintings came from runoff water and that the whewellite, weddellite and calcite in the surface crusts are linked to the presence of mosses/lichens. In addition, the pigment minerals in the pictorial matter samples were of hydrothermal origin, as were the minerals in the colouring matter from the archaeological layers. Although, we were unable to determine whether the colouring matter is identical to the pictorial matter used to make the paintings, our results highlight the need to consider weathering products when analyzing pictorial matter.