Stones from medieval glassmaking: a suitable waste product for reconstructing an early stage of the melting process in the Mt. Lecco glass factory.

The Mt Lecco glass factory was one of the most important production centres in Liguria (Italy) during the 14th and 15th centuries. Archaeological evidence indicates that the whole production cycle took place here. During the glassworking process, production defects such as ‘stones’ were identified and discarded. Stones are partially melted, glass-coated relics of raw materials or fragments of crucible. The study of the microtexture of stones together with microprobe analyses of phases provides a key for understanding the glassmaking procedure carried out in the Mt Lecco glass factory. The melting rate can be inferred from the compositional variability of glass, which suggests fractional melting of the batch. Glass composition indicates that the Mt Lecco production was a mixed-alkali one, probably made of quartz-bearing material as vitrifying agents, plant ashes as fluxing agents and dolomitic limestones as stabilizing agents.