Compositional variability of pigments and related materials used in stone reliefs from the Tula Archaeological Zone, Mexico: Overcoming challenges of a highly restored site

Tula is a monumental complex arranged in terraces and platforms, where the stone architecture is decorated with anthropomorphic and zoomorphic carvings, and polychromed stone reliefs. As a first step for designing appropriate restoration and conservation strategies, the characterization of the color palette of the reliefs was performed. The simultaneous occurrence of salts, conservation materials and pollution represented a major challenge that required a combination of non-destructive in situ analyses and laboratory tests on a limited number of samples. The pigments identified include Maya blue, hematite, jarosite, black earth and calcite, while gypsum was present both as part of the pictorial technique and as an alteration product. Finally, environmental pollution together with water availability was found responsible for the salt damage of the painted surfaces. (C) 2020 Elsevier Masson SAS. All rights reserved.