Combined use of XPS and SEM plus EDS for the study of surface microchemical structure of archaeological bronze Roman mirrors

By means of the combined use of XPS and scanning electron microscopy + energy dispersive spectrometry (SEM + EDS) the study of the surface microchemical structure of two archaeological Roman mirrors is carried out in order to obtain useful information to identify the ancient production technology, the degradation state and, further, for understanding the origin of their high chemical stability and appearance. Indeed, one of the selected archaeological bronze mirrors is characterized by a reflecting surface and the other one by a black and uncorroded surface. The results show that via XPS and SEM + EDS, it is possible to obtain detailed elemental composition depth profiles and microstructural information for the outermost layers of these ancient bronze works of art. The results provide good insight into the nature of the external layers showing the presence of different copper-tin phases and lead selective corrosion and depletion phenomena leading to the formation of complex microchemical structures and, further, show the presence of different chemical states of tin as a function of the mirror appearance. Finally, the results indicate that the combined use of XPS and SEM + EDS has significant potential in tailoring the restoration and conservation methodologies of these high-tin bronze archaeological artefacts. Copyright (C) 2004 John Wiley Sons, Ltd.