An archaeometric approach about the study of medieval glass from Siponto (Foggia, Italy)

Medieval glasses, including feet and rims of chalices, fragments of lamps and globular bottles, coming from the archaeological site of Siponto (Foggia, Italy), were analyzed by Inductively Coupled Plasma Emission Spectroscopy and Graphite Furnace Atomic Absorption Spectroscopy for investigating and defining glass production technology in Apulia (Italy) in the Middle Ages, because of the poor understanding currently achieved on either compositional and technological features of medieval glass items. The examined finds, whether colourless or coloured blue, yellow-green, yellow, pink and red, revealed a typical silica-soda-lime-composition. The chemical analysis and the statistical treatment of data allowed to trace former, flux, modifier and, where it is present, the element responsible for colour, clarifying production technology issues. It has been possible to identify, moreover, objects obtained by recycling of cullets or finished items.Finally, this work evaluates the effectiveness of the statistical multivariate treatment by Principal Component Analysis (PCA), Clustering Analysis (CA) and Factor Analysis (FA) on compositional data to obtain technological information in opposition to the conventional binary oxides diagram, which represent the most common, widely assessed, archaeometrical practice to obtain technological information from compositional data.