Weathering of a Roman glass. A new hypothesis for pit formation on glass surfaces

This paper reports on a study of glass samples found in Baia, Italy. Based on their place of discovery the studied samples should be dated back to the Roman period. The pieces are crusted and pitted On the basis of the observation a new hypothesis is proposed for the pitting of glasses. Visual and microscopical observations indicate that the weathering of the studied glass has led to a multilayer surface structure. Weathering was ascribed to the occurrence of hydrolysis and condensation reactions which would have led to layers of gel-like structure and high silica content. Ageing of the reaction layer would have led to formation of poles. The need to relieve stresses could make pore formation preferential at the glass reaction layer interface. As a result the surface would appear pitted and bubbles should be present in the detached layer when it is sheared off The proposed mechanism also gives a simple explanation of earlier findings.