Searching for the Right Color Palette: Source of Pigments of the Holocene Wadi Sura Paintings, Gilf Kebir, Western Desert (Egypt)

In this article, we discuss the geological, mineralogical, and geochemical characteristics of the proposed sources of pigments used in the Wadi Sura rock art, southwestern Egypt. Colors used in the paintings include white, yellow, and several reddish hues ranging from pale red to dark reddish brown, rare black, and greenish hues. The results of Raman spectroscopy and pXRF techniques on both raw coloring materials and archaeological pigments show that the ancient artists made extensive use of inorganic clay-based pigment (e.g., kaolinite) associated with anhydrite and gypsum. White raw coloring materials were recorded in the field as thin laminated beds and lenses within the Silurian sandstone bedrock and are also present in paleosol layers and reworked fragments mixed with ocher. Raw materials for red and yellow colors are represented by clay-based mixtures of aluminosilicate with iron oxide, hematite, goethite or magnetite, and gypsum. The amorphous carbon and romanechite, as well as goethite and magnetite, could have been the components of the dark brownish pigments widely used in the rock art of the study area. Surprisingly, lazurite was also recognized among the raw materials, although this blue pigment does not seem to have been used in the Wadi Sura rock art panels (however, bluish and greenish traces as violet reddish hues, along with bluish-greenish yellow colors, are reported in the paintings). Lazurite is not well known in the geology of Egypt and has been detected in this study for the first time. The results of our work indicate that access to the Silurian sandstones, mainly located on the northwestern slope of the plateau, may have been one of the factors for choosing this area of the Gilf Kebir for producing rock art images.