Micromechanical properties of banded alterations of archaeological glass fragments

Resistance to plastic deformation on surfaces of excavated glass fragments of late Byzantinic provenance and from early modern manufacturing was studied using Vickers indentation. Each glass surface consisted of a silica-rich alteration layer of consecutive multiple bands, as a result of a dissolution-reprecipitation mechanism of corrosion under long-time acidic conditions. A sharp drop in decrease of hardness and Young's modulus (> 90%) was evident at the pristine glass/alteration layer interface. Stiffness and indent sizes across the alteration bands revealed a corresponding pattern of increasing hardness and Young's modulus towards the outer parts, which indicated clogging of the porous corrosion products. Micromechanical properties of the banded alteration obeyed Gibson-Ashby equation for porous materials of complex microstructure.