Glass beads from Villanovian excavations in Bologna (Italy): an archaeometrical investigation

Excavations performed in the 1970s in the present-day trade fair zone of Bologna brought to light remains of civilisationsof the 8–7th century B.C. Archaeological studies identified a large number of objects which clearly indicated the existence of anextensive Villanovian village. Fifteen blue, turquoise, and dark green glass beads were selected and analysed in the present study.Chemical analyses of major and minor elements were obtained by EMPA, whereas trace elements were determined on selectedsamples by LA-ICP-MS. The occurrence of eventual opacifying agents dispersed in the matrix was attested by SEM observations.The chemical data allow identification of a group of four beads characterised by a mixed alkali composition, typical of FrattesinaFinal Bronze Age production. All the other samples have low levels of K2O (,2 wt%) and relatively high Na2O (.15 wt%). Among these last samples, which can be classified as natron-based glass, a number of blue beads show a high quantity of MgO (about 3 wt%), in combination with a low K2O amount. These low-K, high-Mg glasses also exhibit extremely high amounts of Al2O3, possibly due to the use of Co-bearing alum as colouring compound. Also the trace-element data confirm the division of the natron-based samples into two different sub-groups on the basis of the concentration of V, Cr, Ti and Zr. This suggests that the glass found at this site derivesfrom three different melts. Regarding the opacity of the samples, in most of the cases this effect is due to the dark colour of the glass (i.e., blue, dark green) which hinders the transmission of light. Crystalline particles of calcium antimonate were found only in the turquoise-colour samples.