Analyses of the brown stain on the Parthenon Centaur head

Marbles of Greek origin have been reported to form a brown stain layer, also known as patina or film. Early investigations discovered that this layer is formed by the two calcium oxalate minerals whewellite and weddellite. The origin of this oxalate film is, however, not clear, while one of the hypotheses is that it is a result of bacteria, fungi, or lichen growing on the surface of the marble. The present study characterizes the brown stain from one of the Parthenon marbles in Danish custody using LC-MS-based proteomics aiming to shed light on the possible biological origin of the staining layer. The marbles curated in Copenhagen are particularly interesting because the pieces have been kept indoors since before the onset of the industrial revolution, therefore they have experienced air pollution to a much lesser degree than the marbles still residing at the Acropolis.