Evidence of glass-working, consisting of glass-coated burnt clay and waste glass, has been recorded in several areas of the town. Glass-working areas have been identified at different dates. Pre-Flavian glass debris at Watling House, Watling Street (GM213) suggested that early workshops existed nearby.
At Regis House (KWS94), on the waterfront, a 1st-century warehouse bay was used as a glass workshop. The workshop included a short succession of small furnaces and considerable quantities of waste and broken products. Late 1st-century glass-working debris was also found at Old Bailey (OBA88). At the Inmost Ward, Tower of London and St Dunstans Hill (GM163) two dumps of glass-working debris of late 2nd or 3rd-century date were recorded while a 3rd-century dump was found beyond the city wall at Norton Folgate (NRT85).
Most evidence is centred in the northern part of the town in the 2nd century. At Copthall Avenue (KEY83), in the upper Walbrook, a substantial quantity of residual furnace-lining was found in late 1st to early 2nd-century levels and at Moorgate (MGT87), part of a glass-working kiln or tank furnace was found, dated to AD140-160. Recent finds at Northgate House, Moorgate (MRG95) have revealed further tank furnaces of different construction, blowing waste and waste vessels (cullet) collected for recycling, dating to the early 2nd century. To the east of the amphitheatre at Guildhall Yard (GYE92) very extensive dumps of early 2nd-century cullet were found with evidence of glassblowing waste but no workshop. The size of these dumps signifies a deliberate attempt to gather together discarded vessels in order to provide the raw material for glass-working. It is, therefore, an early example of glass recycling.
Unique among the London assemblages the waste found at Basinghall Street (BAZ05) comes from all stages of the glass-working process. The material seems to be a failed tank of glass, perhaps rubbish thrown out when a workshop was abandoned and the workers stopped production.
The glass-working waste found on these sites does not make it possible to say with any certainty what vessels were being made. It is likely that a range of utilitarian household vessels were being made for the local market. These would have been dishes, bowls and necked jugs or flasks made of the standard naturally-coloured glass. However, there is some indication that at some stages a wide range of better quality vessels were being made in colourless glass.
The evidence for glass-working has shown that the manufacturing processes were located on the periphery of the town or on low quality land alongside other crafts and industries. Furthermore, it would appear that there was only one glass workshop active at any one time. Whether these were permanent establishments or temporary, perhaps seasonal, sites is still open to debate.