Reperti di vetro e pasta vitrea

The glass material coming from the excavation in the area of the church of Sant’Andrea amounts to 187 fragments in total (163 from Sector C, 24 from Sector C1). These are prevalently pieces of body sherds, small in size, rarely recomposable: a common characteristic of the context of this settlement, due to the fact that the material is found in collapse layers, filling layers, floor levels and use layers and which were continuously trampled on. The finds, however, although small, in terms of preservation are in discrete condition; but only a part of them, about a quarter of the whole, show morphologic characteristics which permitted a chrono-typological determination, carried out on the basis of matching with published inventories. Apart from fragments of window glass, the diagnostic finds are attributable prevalently to domestic appurtenances, with a clear preponderance of open vessels, probably drinking vessels, even if for fragments with a simple rim rounded in the flame attributed to the typology of stemmed goblets it cannot be excluded that they belonged to other kinds of containers, such as glasses with a flat bottom or ringed bottom or bottles or lamps. The chronological span covered by collected material results as being very broad, extending approximately from the 6th to the 16th centuries; if the proposed identifications are correct the dating of the finds seems to indicate a significant incidence of the phenomenon of residuality, inferable from the relatively high presence of fragments assignable to the Late Antique/EarlyMedieval period compared with finds of a later age. This fact can probably be explained in that, in both the areas of excavation, the buidings of a more recent period were put up in areas previously occupied by structures dating from the Late Antique/Early Medieval epoch, destroyed and obliterated. As far as possible it was therefore attempted to distinguish two broad groupings on the basis of chronology, even if on the dating of some specimens there remains some doubt and uncertainty. In the group of finds from the Late Antique/Early Medieval epoch are to be found stemmed goblets, a flat based glass, triansate and hollow-stemmed lamps and probably also a glass paste bead. The group of finds dated to the Late Medieval/Renaissance age is composed of chalice glasses decorated with drops, bottles, a phial and numerous fragments of window glass. The archaeometric study focuses on a selection of glass fragments found in Sector C and dating back to the Middle Age-Renaissance period. In the context of technological evolution of glass, this is a crucial period since, starting from the 9th century AD, there is a radical change in the raw materials used for its production both in the East and in the West: natron, the flux typical of the Roman and Early Medieval period, is replaced by ashes of both continental (mainly used in northern Europe) and coastal (in the Middle East and in the Mediterranean area) plants, with consequent influence on the final chemical composition of the glass. The archaeometric analyses, carried out on the Loppio samples, are, therefore, aimed at determining the composition of the raw materials used for their production; classifying the samples on the basis of the compositional groups known in the literature for the period of interest; extending the archaeometric data base on Italian medieval glass and, last but not least, contributing to a better dating of the archaeological finds of this research. The selected archaeological finds are all ascribable to glassware (probably beakers) with a stratigraphic age between the 12th and 16th centuries AD. The chemical composition of the samples was obtained using the electronic microprobe. The results show that all the so far analysed glasses recovered from the sector C of Loppio can be classified as silica-soda-lime glasses, with SiO2, Na2O and CaO contents between 64.3 ÷ 71.5 wt.%, 12.0 ÷ 13.0 wt.%, 6.2 ÷ 8.9 wt.%, respectively. Except for sample 18833, glasses have mean potassium and magnesium contents higher than 2 wt.%, which suggests the use of soda-ash as flux and is consistent with the production technologies of glass of the period under consideration. Aiming at better characterising the production technologies used, the chemical data of the Loppio glasses were compared with those of glasses from the same period and different areas. In particular, considering the importance of the Venetian and Tuscan glass-working areas during the Middle Age and the Renaissance, we compared our data with those from Venetian and Tuscan glass samples, analysed so far, dating from the 11th to the 18th century. The chemical characteristics of the Loppio soda-ash glass is strictly similar to the high-Al Venetian glass of 11th- 14th century, falling in the same compositional range for all considered chemical elements. This suggests the use of poor-quality vitrifying raw materials, made up of quartz-feldspatic sands and probably Levantine ash as a flux, as typical of Venetian glass production of that time. A certain amount of manganese was also added to the batch, possibly with the aim of decolourating the glass, a process that, however, failed in the specific case, being all Loppio glasses still coloured in olive-green. The compositional affinity of these Loppio soda-ash glass with Venetian glass of 11th-14th century also makes it possible to restrict, on an archaeometric basis, the dating of the vitreous archaeological finds of sector C to the 14th century. Sample nr. 18833 is very different from all the other findings in Loppio. It shows higher silicon and lower potassium and magnesium contents (both lower than 1.5 oxide wt.%), which suggest the use of natron as a flux. This sample shows strong compositional affinities with glasses of the Levantine group II, which dates from the 8th to the 9th century. The finding at the archeological site of S. Andrea in Loppio of a glass with this particular composition represents a unicum in Italy, making this study a contribution of special relevance in the panorama of the archaeometric studies conducted so far on the Italian medieval glass.