From Micro- to Nano-Arrangement: Alteration Products in Archaeological Glass from Marine and Land-Based Environments.

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/nanostructural arrangements and the possible role played by chemico-physical conditions on the morphology and composition of the alteration products. The materials here analysed are glass fragments coming 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 1800 years, 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. Results are subsequently compared with those from alteration products of buried Roman and Medieval glass from the Italian area, e.g., Vicenza, Grado, and Pozzuoli. The analytical techniques employed in this study are a) scanning electron microscopy for microtextural morphologic inspection of alteration layers; b) electron microprobe for chemical analyses of both pristine and altered portions; c) transmission electron microscopy to define nanostructural details of the alteration crusts.