X-ray photoelectron spectroscopy and scanning Auger microscopy studies of bronzes from the collections of the Vatican Museums

X-ray photoelectron spectroscopy (XPS) and scanning Auger microscopy (SAM) have been used to study two ancient objects of the Vatican Museums: a Roman bronze, found in seawater, and an Etruscan bronze, found in soil. The main purpose of this work is to evaluate the degree to which XPS and SAM are capable of revealing the effects of different burial sites on the surface microchemistry of these bronzes. We find that seawater causes the build-up of copper sulfides and lead carbonates/oxides on the bare surface of the Roman object, whereas the original patina is rich in copper chlorides, although sulfides are still detected. Moreover, fair evidence is given that during its use this bronze had been subjected to deliberate smearing with oil or pitch for conservation purposes. By way of contrast, soil made the surface of the Etruscan bronze rich in a mixture of copper chlorides and oxides. Tin, entirely present as an SnO2-like phase, is more abundant, as is metallic copper, in the Etruscan bronze than in the Roman one. These results compare favorably with findings of other authors on 'modern' Cu,Sn. In this same object, SAM highlights lateral chemical heterogeneities with a spatial resolution similar to 2,000 Angstrom. Our results are related to other studies conducted on bronze objects analyzed with bulk-sensitive methods, as well as to the reports of historical sources. (C) 1999 Elsevier Science Ltd. All rights reserved.