Ubiquitous presence of laminae in altered layers of glass artefacts

摘要

Whatever the chemical composition and the origin (natural or man-made) or the surrounding environment is, glass materials undergo alteration processes leading to the modification of their structure and chemical composition. Similar alteration patterns can be observed in different historical glass types, especially alteration layers characterized by a laminated structure. The study of medieval stained glass windows (14th century AD, from Northern France) and Roman glass blocks (2nd century AD, from a shipwreck in the Mediterranean Sea) with several centuries of exposure in atmospheric and marine conditions, respectively, show that laminated features, commonly described at micro-scale (e.g. lamination), can also be found at the nano-scale (laminae) using TEM analysis on FIB ultra-thin section. These features develop on different alteration layers - in the gel layer for medieval glass and in crystalline secondary phases (smectites) for Roman glass - showing that the formation mechanisms vary according to the exposure environment and the chemical composition of the glass.