Glasses on the seabed: surface study of chemical corrosion in sunken Roman glasses

The current work aims to describe surface weathering of ancient glasses in marine environment. All data are collected using different techniques: optical microscopy, RGA, surface techniques (XPS, SEM and SIMS). Three types of glass weathering have been observed: white glass, glossy glass and glass showing growth rings. A compact structure characterizes white glasses, while a porous structure with flaked layers is typical of glossy glasses. White glasses show different abundance of characteristic elements or molecules (Mg(II), Sb(V), Ti(IV) and micro-crystalline silica). Glossy glasses, instead, are characterized by peeling layers of nearly pure silica glass, with small differences in composition owing to ionic mobility phenomena. Data suggest a time relation between white and glossy glasses. Visible growth rings characterize the third class of glass. They are made of titanium and antimony compounds centers surrounded by many rings with the same composition. Their temporal evolution has been explained according to the theory of ‘Liesegang rings’. Hypotheses on antimony and titanium origins are reported.