Study of sea water influence on chemical and physical degradation of Roman glass

From ancient times to today glasses, generally based on siliceous oxides cooled to a hard condition to avoid crystallization, have been extensively used, for their chemical-physical durability. Indeed, glass is one of the materials most frequently discovered during archaeological excavations. The degradation induces the loss of brightness and transparency, and the formation of pits, crystals and patinas. Sometimes peeling layers may appear, too. All these phenomena alter irreversibly the aesthetic appearance of the glassworks. The research in this field, initially focused on the knowledge of history, composition and technology of the manufacture of works of art is trying now to rationalize the problems connected with degradation processes through, both, very sensitive characterization techniques and model experiments simulating degradation phenomena. In this work we deepen the analyses of glass degradation regarding samples coming from the Roman ship Iulia Felix found on the seabed of Grado lagoon (Italy) and dated to the II century A.D. Their surfaces have been investigated through XPS (X-Ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry) to understand water effects on glass degradation and interesting considerations on the mobility of the present ionic species are proposed. We also report the results of micro-XRF and synchrotron-XRD analyses that will allow us to single out the various crystallization species present resulting from the degradation phenomena of these glasses.