Iron speciation in ancient Attic pottery pigments: a non-destructive SR-XAS investigation

The present work reports a detailed investigation on the speciation of iron in thepigments of decorated pottery fragments of cultural heritage relevance. Thefragments come from the Gioiosa Guardia archaeological site in the area of the‘Strait of Messina’ (Sicily, Southern Italy), and date back to VI–V century BC.The purpose of this study is to characterize the main pigmenting agentsresponsible for the dark-red coloration of the specimens using non-destructiveanalytical techniques such as synchrotron radiation X-ray absorption spectroscopy(SR-XAS), a well established technique for cultural heritage andenvironmental subjects. Absorption spectra were collected at the Fe K-edge onthe Italian beamline for absorption and diffraction (BM8-GILDA) at theEuropean Synchrotron Radiation Facility in Grenoble (France). In order todetermine the speciation of Fe in the samples, principal component analysis andleast-squares fitting procedures were applied to the near-edge part of theabsorption spectra (XANES). Details on the local structure around the Fe siteswere obtained by analyzing the extended part of the spectra (EXAFS).Furthermore, an accurate determination of the average Fe oxidation state wascarried out through analysis of the pre-edge peaks of the absorption spectra.Samples resulted composed of an admixture of Fe2O3 (hematite or maghemite)and magnetite (Fe3O4), occurring in different relative abundance in the darkandlight-colored areas of the specimens. The results obtained are complementaryto information previously obtained by means of instrumental neutronactivation analysis, Fourier transform infrared absorbance and time-of-flightneutron diffraction.