Organic substances at metal surfaces: archaeological evidence and the Elder Pliny's account

This paper discusses the implications of X-ray photoelectron spectroscopy (XPS) and scanning Auger microscopy (SAM) results that revealed the presence of sizable amounts of carbon-bearing species at the joint of a Roman lead pipe (fistula) and at the surface of a Roman bronze statue. The detailed description in Pliny's Naturalis Historia on the use of oil, pitch and bitumen in metallurgical contexts offers convincing grounds for an interpretation that the experimental findings arise from deliberate addition of these substances to lead and bronze. The surface of ancient metals is in itself a source of archaeological evidence, and XPS/SAM techniques are ideally suited to bringing them to light.