Chemical and isotopic provenance study of Final Bronze Age glass artefacts from Central Italy

Glass is an amorphous solid found in nature, that Man has been manufacturing since ancient times mixing multiple components: a vitrifying agent, a stabilizer, a fluxing agent and a (de)colorant. Different elements come primarily from different components, therefore combining chemical and isotopic data, and comparing them with existing databases, it is possible to reconstruct the origin of the raw materials, and thus the provenance of the glass artifacts. This study focused on the chemical (major, minor and trace elements) and isotopic (Sr, Nd, Pb) characterization of five vitreous samples dated to the Final Bronze Age – Early Iron Age (1126 a.C. – 897 a.C.) from the archaeological site of Paduli, lago di Piediluco (Rieti). The five samples were selected as the most representative among all glass samples found in the site during previous sampling campaigns. One of the samples (blue vessel’s fragment with white decorations) has chemical (i.e., Al2O3, Zr, Ti, REE) and isotopic (Sr and Nd) characteristics that point to a Levantine origin. Sr isotope ratios, as well as CaO, Sr, U, and Ba contents, indicate the use of aragonitic shells of marine organisms as stabilizer. Pb, probably used to favour glass matrix fluidity, has an isotopic fingerprint comparable to that of the Taurus ores (Turkey), known to be exploited in eastern Mediterranean glass production. The white decorations are obtained by the neocrystallization of Ca antimoniates, made with Sb of possible Caucasian origin. The other four samples (two annular beads, one turquoise and one blue, a blue bichrome horned-impressed eye bead and a blue cylindrical bead with white decorations) are classifiable as mixed alkali glasses and present a composition that is typical of European vitreous materials. Chemical and isotopic fingerprint of these beads link them to Frattesina, a well-known glass production centre active during the Bronze Age. The differences among the samples derive from: i) the possible use of different types of stabilizers (CaO), recognizable through the absolute concentrations of Sr, Ba and U, as well as through the Sr-isotopic composition ; ii) the use of sands (as a vitrifying agent source) with variable Nd isotopic composition, probably purified beforehand, and linked to Po River and Adige River; iii) the addition of colourants with different composition and origin. Pb isotopic ratios, characteristic of the source of colorant, suggest the use of metals coming from Trentino-Alto Adige ores for all samples except for the cylindrical bead, that seems to be linked to Austrian ores. Its white decorations are obtained through crystals of wollastonite. Glass samples found in Paduli archaeological site seem therefore to originate from a well-known glassmaking centres active during the Late Bronze Age (Frattesina and production centres in the Levant), suggesting that the site was an important trade centre between North Italy and the Eastern Mediterranean.