With the incorporation of Syria-Palestine in 60-80 BCE and Egypt in 30 BCE into the Roman Empire, the Roman glass industry grew to unprecedented levels. Products of this expanding industry include a group of polychrome mosaic bowls and other open vessels, produced by slumping techniques in the preceding Hellenistic Period. Production of these strongly coloured vessels, associated with elite contexts, declined dramatically in the first millennium CE, as the spread of glass-blowing made inexpensive transparent glass accessible to a much larger market. This class of objects has been found at archaeological sites across the Mediterranean and Europe; most notably in the Aegean and Italy, but also in Crete, North Africa, Britain, Switzerland, and Spain. However, less is known about where the glass used in their manufacture was produced. This study aims to provide a clearer picture of their provenance, movement and the technologies employed to colour and opacify the glass using compositional and structural analysis. 38 cast mosaic vessel fragments from the Victoria & Albert Museum have been analysed for 58 major, minor, and trace elements using LA-ICP-MS in the Wolfson Archaeological Science Laboratories at the UCL Institute of Archaeology. Non-invasive Raman Spectroscopy was carried out on the objects in the Conservation Science Laboratory at the Victoria & Albert Museum to identify opacifiers. Opacification was generally due to compounds of antimony and metallic copper but in several cases high concentrations of tin are present. Principal component and hierarchical cluster analyses were used to treat the chemical data, and three main compositional groups were identified based on the minor and trace elements (especially Ti, Zr, Al, Th, and La) commonly associated with the glass-making sand. Two groups comprise glass thought to have originated in Egypt and one in Syria-Palestine. Some objects previously thought to have been made in Egypt on the basis of find location and/or typology appear to have been made from Levantine glass, and comparison with well-provenanced mosaic glass excavated in Egypt suggests that these vessels were instead manufactured in Italy or the Levant.