Origins of early Imperial Roman fused mosaic glass

The Roman glass revolution, typically characterised by the adoption of the blowpipe, was preceded by a significant expansion in the production of glass bowls made by slumping in the Hellenistic period. Mosaic vessels, made of brightly coloured glass in complex patterns represent the most sophisticated expression of this technique. One hundred and one polychrome glass objects dating to the first centuries BCE and CE and including 65 mosaic glass bowls were analysed for 58 elements using Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS). Multivariate statistical analysis of the compositions of 443 individual coloured glasses identified three groups. Groups 1a and 1b are closely related and are relatively rich in TiO 2 , ZrO 2 , HfO 2 , Nb 2 O 3 , and ThO 2 , attributable to origins in Egypt, while Group 2 is rich in Al 2 O 3 and REE and consistent with an origin on the Levantine coast. Mosaic plaques and vessels found in Egypt were made almost exclusively of Egyptian glass. Vessels acquired elsewhere, probably Italy, were either made of only Egyptian glass, of only Levantine glass, or combined glass from both regions in a single object. Given the low abundance of Levantine glass in the Egyptian objects, and the scarcity of mosaic glass excavated in the Levant, the vessels containing glass from both sources and those made in only Levantine glass are likely to have been made in a third region. Thus the compositional data support the view that early Roman slumped mosaic bowls were predominately manufactured outside the eastern Mediterranean, probably in Italy. • Minimally invasive trace element analysis of a large corpus of Roman mosaic glass. • A new glass group has been identified, produced using a vegetal ash component. • The mosaic glass was likely made in Italy due to composition of the base glass.