μXRF and μXANES to unequivocally disclose the nature of the black phases and Hg-Cl and Hg-S-Cl species on blackened Roman cinnabar fresco pa

The blackening of red cinnabar pigment is a major problem of conservation for the artworks containing it. To explain the black color, different hypotheses have been proposed, but none of them has been fully confirmed. This proposal aims to identify the newly formed black phases, comparing the results in model fresco paintings subjected to accelerated weathering experiments and the ones in blackened cinnabar fresco painting samples from the Archaeological Park of Pompeii. The possible presence of additional Hg-Cl and Hg-S-Cl species, not easily detectable by conventional laboratory techniques, will be also confirmed. The resulting information will allow refining the understanding of the chemical reactivity leading to the darkening of cinnabar, contributing to develop appropriate conservation protocols to preserve this precious pigment. To achieve these objectives, a combination of µXRF, Cl and S K-edge µXANES and Hg L3 edge µXANES in HERFD mode is crucial.