When Red Turns Black: Influence of the 79 AD Volcanic Eruption and Burial Environment on the Blackening/Darkening of Pompeian Cinnabar.

Bruno De Nigris,Juan Manuel Madariaga,Silvia Pérez-Diez,Alberta Martellone,Africa Pitarch Martí,Massimo Osanna,Anastasia Giakoumaki,Silvia Fdez-Ortiz De Vallejuelo,Maite Maguregui,Nagore Prieto-Taboada

doi:10.1021/acs.analchem.1c02420

Abstract

It is widely known that the vivid hue of red cinnabar can darken or turn black. Many authors have studied this transformation, but only a few in the context of the archeological site of Pompeii. In this work, the co-occurrence of different degradation patterns associated with Pompeian cinnabar-containing fresco paintings (alone or in combination with red/yellow ocher pigments) exposed to different types of environments (pre- and post-79 AD atmosphere) is reported. Results obtained from the in situ and laboratory multianalytical methodology revealed the existence of diverse transformation products in the Pompeian cinnabar, consistent with the impact of the environment. The effect of hydrogen sulfide and sulfur dioxide emitted during the 79 AD eruption on the cinnabar transformation was also evaluated by comparing the experimental evidence found on paintings exposed and not exposed to the post-79 AD atmosphere. Our results highlight that not all the darkened areas on the Pompeian cinnabar paintings are related to the transformation of the pigment itself, as clear evidence of darkening associated with the presence of manganese and iron oxide formation (rock varnish) on fragments buried before the 79 AD eruption has also been found.

Highlights

It is widely known that the vivid hue of red cinnabar can darken or turn black
This work shows how the state of conservation of the Pompeian cinnabar pigment varies depending on its protection against the pre- and post-79 AD atmospheres
Gypsum has been systematically identified in the blackened areas of the pigment exposed to the pre- and post-79 AD atmospheres (e.g., House of the Golden Cupids)

Summary

Introduction

It is widely known that the vivid hue of red cinnabar can darken or turn black. Many authors have studied this transformation, but only a few in the context of the archeological site of Pompeii. Some of the pigments applied on the walls of Pompeii experienced transformations due to the eruption, such as the blackening process of hematite (α-Fe2O3)[1] and the dehydration of yellow ocher (goethite, α-FeOOH) into hematite.[2,3] A recent study has shown that another reason for the degradation of the mural paintings of Pompeii is the crystallization of salts coming from the pyroclastic materials ejected in the 79 AD eruption.[4] In addition, since the first archeological excavations in the 18th century, the archeological park has suffered a continuous decay, due to its exposure to the modern atmosphere and the (former) application of restoration products that are no longer used.[5]. The study of ancient sources[6,7] and archeological records demonstrates that red cinnabar (α-HgS) has been used as a pigment since antiquity This precious pigment, employed in the mural paintings of the archeological site of Pompeii, suffers from blackening. The altered cinnabar/ vermilion shows brownish to grayish hues.[11,12]

Objectives

Results

Conclusion