Surface and interface microchemistry of archaeological objects studied with x ray photoemission spectroscopy and scanning Auger microscopy

We report x ray photoemission spectroscopy (XPS) and scanning Auger microscopy (SAM) studies of a Roman lead pipe 'fistula' and a Roman bronze sample. SAM analysis shows that the lead is much more oxidized in the original patina than in the naked surface of the fistula. Comparisons performed between large-area XPS measurements and microscopic SAM measurements indicate that there is a huge lateral chemical inhomogeneity in the surface composition of the bronze. Auger point spectra and elemental Auger imaging reveal, with a sub-micron spatial resolution, that tin is exclusively associated with oxygen in both materials, and the lateral distribution of these two elements is complementary to that of chlorine.