From micro- to nano-arrangement: alteration products in archaeological glass from marine and land-based environments

The alteration of archaeological glass in natural environments is a very complex process affected by many factors, including glass characteristics and external conditions, such as climate, temperature, time, pH, and composition of aqueous solution (Newton and Davison 1996). The present study was carried out on the alteration products of glasses from various archaeological sites, both marine and land-based, in order to understand the relationships between optical features and micro/nano-structural arrangements, and the possible role played by chemicophysical conditions on the morphology and composition of the alteration products. The materials analysed here are glass fragments originating from the cargo of the Roman ship Iulia Felix, discovered at a depth of about 15 m off Grado, in the northernmost part of the Adriatic Sea (Italy). These fragments, exposed to the marine environment for about 1,800 years, were buried in carbonatic sand and subsequently cemented by calcite. All the samples show an exceptional degree of alteration and represent an elective case for the study of alteration processes in glasses, because the geochemical parameters of the conservation environment are known. The results are subsequently compared with those from alteration products of buried Roman and Medieval glass found in sites in the Italian area, e.g., Vicenza, Grado, and Pozzuoli. Some samples show signs of decay due to their prolonged contact with soil and groundwater