From the Journal of Raman Spectroscopy, a report called "Field Raman analysis to diagnose the conservation state of excavated walls and wall paintings in the archaeological site of Pompeii."
Abstract:This work presents the results of field Raman analyses, assisted by a hand-held energy dispersive-X-ray fluorescence spectrometer, to experimentally determine the composition of compounds present in the walls and wall paintings of two Pompeian houses, one with many luxurious decorative elements (the House of Marcus Lucretius, Regio IX, Insula 3, House 5/24) and a more modest building (Regio IX, Insula 3, House 1–2). These houses were excavated 150 years ago, and the majority of the rooms have been exposed outdoors. The chemical attacks of the acid gases and the biological colonisation can be considered the most serious problems of the archaeological remains from Insula IX 3 of Pompeii. The walls and wall paintings exposed to the rain-wash are the worst preserved ones, probably due to a continuous cycle of SO2 attack to the original materials, involving loss of plaster. This severe decay was not observed in the rooms covered by roofs; in these last rooms, the most noticeable pathologies are the presence of high humidity in the walls and the elevated amount of efflorescences.
A PDF of the article can be downloaded from the Wiley Publications website.