The archaeological remains of the English medieval glass industry in Staffordshire

• Results show the development of the Staffordshire glass industry overtime. • SEM-EDS characterisation of glass and crucibles from dated sites. • Comprehensive comparison of the Staffordshire and Weald industries. • Significant contamination from recycling in early window glass. • Higher sodium glass and sandstone grogged crucibles from the late 16th century. Staffordshire in the Midlands of England was home to an important medieval and post-medieval glass industry, including making glass for York Minster. The area had ample wood fuel for the furnaces and sources of the plant ashes required to make the glass. Far less is known about the Staffordshire industry however, compared to the competing Wealden glass industry in the South. There have been few excavations, but many more furnace sites have been located by geophysical survey and field walking, and surface finds of crucible and glass were recovered. This study reports on these surface finds, which reveal how glassmaking in Staffordshire changed over time and differs from practice in the Weald. The results indicate that the Staffordshire region was slightly dominant over the 13th to 15th centuries and the glass made can be differentiated from Wealden glass by the manganese content and the ratio of calcium to potassium oxides. There is considerable recycling of imported European window glass cullet resulting in contamination, particularly with lead and iron, and much more variation in the glass composition than observed in Wealden glass. The fortunes of the industry in Staffordshire decline later in the 16th century, in favour of the Wealden industry, at which time the type of glass produced in each region and the crucible technology also diverge. The later Staffordshire glass routinely contains more sodium than the contemporary Weald glass. This sodium-rich formulation survives the transition to coal-fired furnaces and may be the forerunner of later mixed alkali glass compositions.