Glass consumption in post-Medieval Flanders: the validation of a new spectroscopic tool

Archaeometry research on historic glass primarily relies on understanding their chemical composition. Our research group has extensively used UV-Vis-NIR absorption spectroscopy in situ for this purpose over the past decades. Recent research targeted naturally coloured or decoloured window glass with a post-medieval signature from the Low Countries. We successfully distinguished two subgroups of High Lime- Low Alkali (HLLA or Ca-rich) glass associated with two distinct timeframes: the late 15th to mid-16th centuries and the latter half of the 16th to 17th centuries, respectively. This classification is based on selected optical metrics reflecting variations in ionic and atomic iron contents. The introduction of this innovative tool allows us to address a gap in literature concerning glass composition and consumption in the southern Low Countries spanning the 15th to 17th centuries. Given that recording a single measurement takes less than a minute, the tool facilitates the rapid screening of large collections of glass fragments. We present further validation of the technique by studying archaeological glass fragments from various excavation sites situated in Bree, Mechelen and Ronse. The research findings have confirmed the efficacy of the technique, as glass from different periods between the 15th and 17th centuries exhibited distinctive optical properties. Furthermore, the determined values of the associated optical metrics corresponded with those of previously researched sites, and additionally, they allowed us to fine-tune the mapping between glass purity, production technique and shape. This first-line approach might be beneficial for glass researchers seeking to analyse post-medieval naturally coloured glass using non-destructive methods.