Characterization of the alteration processes of historical glasses on the seabed

Glass objects are common in shipwrecks since they are associated with ordinary glassware or commercial products. The alteration pathologies of historical glasses from two wrecks from the Mediterranean Sea were analyzed to characterize their alteration mechanisms. The results of this research proved that the alteration layers presented a moderate content of Na2O, similar to the average salinity of the ocean, and a high content of Al2O3 due to an extremely basic environment during the corrosion process. The biofouling layer protected the glass surfaces. Dark deposits with a high content of MnO were observed in the most instable glass. •The alteration depended on the chemical composition of the glass and the time it was underwater.•The alteration pathologies depended on the relation of fluxes/stabilizers in the glass.•The friction of the sediment from the seabed formed long marks of aligned curvilinear pits.•The high content of Al2O3 and MgO in the alteration layers was related to advanced corrosion states.•Algae colonization protected the glass surface.