Estudio analítico-estructural de un espejo romano del siglo III perteneciente al conjunto arqueológico de Baelo Claudia (Bolonia, España)

Résumé

This paper describes the process of characterization of a third century Roman mirror belonging to the funds of the Baelo Claudia archaeological site (Bolonia, Spain) using optical microscopy and scanning electron microscopy (SEM) combined with chemical analisis using X-ray spectroscopy (EDX) and X-ray difraction (XRD). The study was based on a cross section of a portion of the sample. The matrix presents a fairly uniform grain size, with small withe globular inclusions of lead, surrounded by a relatively continuous coating but with a very variable tichkness. The average composition of the matrix is a bronze with about 10 % by weigth of Sn and 5-6 % Pb. The contaminants are C, O, and Cl. The presence of a certain amount of Pb is charcteristic of Roman bronzes (Ingo et al., 2004), while the Cl may be associated with the marine environment in the archaeological site, is a selective corrosión process or dealloying, with almost total loss of tin in some areas. On surface, there are two different layers formed by the less noble metals with the elements of the environment. The inner layer, thinner, has higher contents in C, O and Cl, about 10 % Cu, 25 % Sn and 37 % Pb, while the outer layer, thichker, has a hig content Pb 69 % and almost no Sn. It has been determinated that the cause of alteration of the matrix after a long period of exposuto to the marine environment in a archaeological site,