Bronze roman mirrors: the secret of brightness

• DOI: 10.1007/s00339-006-3535-y
• Publication Date: 2006-03-20T16:36:38Z
• Authors: G.M. Ingo; P. Plescia; E. Angelini; C. Riccucci; T. de Caro
• Keywords: 0103 physical sciences; 01 natural sciences; corrosion; artefacts; silver

The surface microchemical structure of high tin leaded bronze Roman mirrors has been studied by means of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and optical microscopy (OM) techniques. The results allowed understanding of the origin of their high chemical stability and silvery-lustrous appearance. Indeed, some areas of the selected Roman mirrors are still characterised by a highly reflective and silver coloured surface even though they have been buried in the soil for about 2000 years. The micro-chemical results obtained from these areas have revealed that the mirror surface was tin enriched via inverse-segregation phenomenon by tailoring the cooling parameters. Furthermore, the presence of tin could be likely enhanced via cycles of oxidation and selective copper corrosion processes, thus resulting in a tin surface enrichment as a semi-transparent amorphous-like tin oxide (SnO(2)) film, as well as a copper depletion at the outer surfaces.