A multitechnique study of archeological bronzes

We used XPS, X-AES, synchrotron radiation-induced total electron yield X-ray absorption spectroscopy (XAS), synchrotron radiation-induced photoelectron microscopy (PEM), and electron-probe microanalysis (EPMA) techniques to explore the elemental and microchemical properties of two tin-bronzes (denoted A and B) found at a necropolis located in Fossa (Abruzzo, Italy), and dating from the late ninth century B.C. EPMA shows that the bulk elemental composition of the two bronzes is very much alike as far as the leading metals are concerned, whereas the main differences are limited to the composition of trace elements (A is notably richer in Pb and much poorer in Co). PEM highlights lateral chemical inhomogeneities with a spatial resolution in the submicron range. X-AES Cu L 3 MM spectra show that the content of metallic copper is more abundant in the surface region of A than in B. XPS finds that the amount of carbon-bearing species is about 40% more abundant in the former sample. A significant enrichment of metallic copper at the surface of the same bronze is confirmed by XAS Cu L 2,3 edge experiments. We interpret the 'high' carbon content found at the surface of bronze A as arising from intentional rubbing with organic substances, e.g. oil. The fact that the same bronze features a higher 'metallization' of surface copper suggests that such a procedure proved successful in minimizing the oxidation induced by the surroundings. We discuss the diagnostic potential of our multitechnique approach as a means for studying the surface chemistry of ancient metalwork.