X-RAY PHOTOEMISSION SPECTROSCOPY AND SCANNING AUGER MICROSCOPY STUDIES OF A ROMAN LEAD PIPE FISTULA

We report scanning Auger microscopy (SAM) and x-ray photoemission spec troscopy (XPS) analysis of a Roman lead pipe ''fistula'', the main emp hasis being placed on the comparison between the surface and interface chemical composition of the joint and of the rest of the pipe. We fin d that the ''tertiarium,'' a Pb-Sn alloy that the Romans used for sold ering the joint, has a beneficial effect in limiting the formation of white lead, 2PbCO(3).Pb(OH)(2). Comparison measurements performed in t he alloy and the pure separate metals show that tin markedly limits th e ambient surface oxdation of lead. Conversely, tin is much more oxidi zed in the alloy than when analysed alone. Auger point spectra indicat e that carbon is the main surface contaminant of the patina of the fis tula, and Auger imaging is used to pinpoint, with a spatial resolution of similar to 0.5 mu m, the distribution of this element at the inter face of a lead/tertiarium solder, performed according to the procedure s described by Plinius. The diagnostic capability of Auger transitions of lead and tin for distinguishing between different phases is discus sed on the basis of their chemical shifts and surface sensitivities.