Roman and late-Roman glass from north-eastern Italy: comparing raw materials and production technologies of vessels and mosaic tesserae

Abstract The present research focuses on the archaeometric study of glasses circulating in north-eastern Italy between Roman times and Late Antiquity with the aim of clarifying raw materials and production technologies. Unlike the approach generally used in the study of glass, which focuses on one of the two classes of materials, vessels and vitreous mosaic tesserae are here addressed in parallel, in order to have a wider picture on the circulation of glass and glass-technologies in the area. The glass vessels here examined come from the most important north-Adriatic harbours of the considered time span: Classe (Ravenna) and Aquileia (Udine). The assemblage of Classe, mainly composed of working wastes and drinking vessels dated to the 5th-8th century, was excavated in the productive area of the harbour of Classe and is thought to derive from a glass workshop. The assemblage excavated in the domus of Tito Macro in Aquileia comprises mainly tableware dated to the 1st-8th century, and some working indicators including chunks. The opportunity of analysing vessels and glassworking wastes excavated in the two cities allows speculating on the composition of locally-worked glass, the location of supply of raw materials and trade routes. The glass tesserae here investigated come from three sites: the disrupted decoration of the Roman buildings excavated under the church of Santa Maria Maggiore in Trento (Italy) and dated to the 2nd-4th century; the disrupted decoration of the Roman villa of Torre di Pordenone dated to the 2nd-5th century AD; and the in-situ mosaic of the Domus delle Bestie Ferite in Aquileia, dated to the second half of the 4th century. The tesserae show a wide chromatic range, comparable in the three sites, that allows direct comparisons. Chemical, textural and mineralogical analyses were conducted by means of an articulated set of analytical methods aimed to obtain the highest standards of precision and accuracy. The analytical methods employed are OM, SEM-EDS, XRF, EMPA, MC-ICP-MS, XRPD, FORS, EPR, and Micro Raman Spectroscopy. The two sites of Classe and Aquileia are characterized by the presence of glass compositions referable to the late Antiquity, with a high degree of comparability in terms of chemical composition and isotopic signatures, which allow hypothesizing that the two cities had similar trade routes from similar supply areas located along the eastern Mediterranean shores. The examination of the mosaic tesserae highlighted a compositional uniformity in the sites of Pordenone and Trento, in which base glass, colouring agents and opacifiers are characteristic of the Roman time; differently, the mosaic of Aquileia shows a greater variety of chemical compositions and colouring/opacifying techniques, partly referable to the Late Antiquity, which indicates a prompt reception of technological innovations