Analysis of Late Antique and Medieval Glass from Koper (Capodistria, Si): Insight into Glass Consumption and Produc-Tion at the Turn of First Millennium CE

A series (n=22) of glasses from the site Kapucinski vrt (garden of the Capuchin monastery, 5th-17th c. CE) in Koper (Capodistria), a port town in northern Adriatic, was measured by a combined PIXE and PIGE method. Koper has been continuously populated since late Roman period with a rich medieval history, thus offering an opportunity to study Early Medieval glass. Stemmed goblet fragments, in the original publication dated between the 6th-9th c. CE, and several other vessel types (beakers, flasks or bottles, lamps) were selected for analysis. The measurements were expected to show the trends in glass production and consumption from Late Antiquity until the Middle Ages, notably the transition between the natron to plant ash glass and supply of fresh glass. Among the set of 22 glass vessel fragments both natron and plant ash glass were identified. For finer classification we relied on a newly developed method of Euclidean distances with respect to major concentrations. Natron glass was of the types of Foy 2.1 (9 examples), Magby (2 examples) and Levantine I (Apollonia; 2 examples). Two glasses remain undetermined but testify Egyptian origin. Most natron glasses show signs of recycling. Among the three unrecycled glasses (about 20% of the whole set) there are the two examples of Levantine glass and a Magby glass lamp; this may indicate a modest supply of fresh glass during the period. Plant ash glass may be attributed to the Early or High Middle Ages, exploiting purified alkalis of the Levantine coasts (known as alume catino in later Venetian glassmaking), while the admixture of impurities in the siliceous sands suggest circulation and consumption of glass that was produced and traded in the eastern Mediterranean since the 10th centuries onwards.