Microbiologically influenced corrosion of archaeological artefacts: characterisation of iron(II) sulfides by Raman spectroscopy

Abstract Archaeological objects are exposed to the action of micro‐organisms when they lay in a biologically active environment. The presence of iron sulfides in the corrosion system testifies in most cases that the degradation was influenced by sulfate‐reducing bacteria. Iron sulfides and other iron/sulfur‐containing compounds were detected by micro‐Raman spectroscopy in rust layers of archaeological ferrous objects and in wet wooden fragments contaminated by iron, extracted from ancient wrecks. Although mackinawite (FeS) is very reactive towards oxygen, this phase was observed in each sample. Its crystallisation levels and oxidation states could be differentiated. Greigite (Fe 3 S 4 ) was also identified by means of X‐ray diffraction, used when possible as a complementary analytical tool. Known as the result of the oxidation of mackinawite, greigite was likely to form during the experiments carried out without any protection against air. It was then possible to describe the formation and oxidation processes of iron sulfides in archaeological iron artefacts or in organic materials contaminated by iron. Copyright © 2010 John Wiley & Sons, Ltd.