Blackening of red cinnabar and malachite in historical Roman wall paintings: speciation of Hg and Cu by means of FY-TEY XAS mapping

The present study aims at ascertaining the valence state speciation of the transition elements (Hg and Cu) in the blackening processes of cinnabar (α-HgS) and malachite (Cu2(OH)2CO3) in order to better understand not only the main suspect but also the mechanism and the intermediate products involved in this darkening. The case studies are provided by an Ostia Antica (one of the most significant archaeological sites in Italy) painted fragment, characterized by the presence of cinnabar, and two mock-ups purposely realized to simulate the original surfaces of the mural paintings in the Roman Catacombs of St Mark, Marcellian and Damasus (Rome, Italy). An accurate X-ray Absorption Spectroscopy (XAS) investigation using FY and TEY mapping could allow to clarify the active mechanisms, ascertaining the effective metal speciation, thus providing a clue in the understanding of the darkening process.