Surface and interface analysis of a Roman lead pipe “fistula”: microchemistry of the soldering at the join, as seen by scanning Auger microscopy and X-ray photoelectron spectroscopy

Abstract

Scanning Auger microscopy (SAM) and X-ray photoelectron spectroscopy (XPS) are used to study the surface and interface chemical composition of a Roman lead pipe (fistula). Experimental evidence is provided that the Romans used tin for soldering the join, and the chemical nature of the single elements, e.g. whether in metallic or combined form, is identified. SAM discloses the segregation of the chemical elements with a sub-micron spatial resolution, and large deviations in the quantitative results are found relative to the large-area averaged XPS results. Elemental depth profiles are obtained from all over the body of the pipe: we find that the lead is less oxidized at the join, and this region contains many more hydrocarbon species, which we interpret as deriving from the use of oil for anti-oxidizing purposes. Our experimental findings are consistent with Plinius' report on the lead-tin soldering techniques used in the Roman world.