The results of a programme of compositional analysis on a series of emerald green glass vessels of known form and date suggest that emerald green vessels have distinct characteristics that set them apart from most contemporary glasses. These specific compositional peculiarities presented here will be evaluated in the context of the varieties of vessel forms produced in the colour. In the light of our findings we will suggest a number of ways forward in the understanding of the structure of the early Roman glass industry. •1stC emerald green glass differs compositionally suggesting it was coloured at source.•It is not used for certain common forms raising questions of secondary supply systems.•Some forms have higher Pb, suggesting links to early Pb-Sb colourless glass production.•The alkali is ambiguous; low-K soda ash(es) or ash+natron (linked to colour formation).•The trace element fingerprint is complex, but an Egyptian provenance is proposed.