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Glass making underwent three revolutions between 1550 and 1750. David Crossley, the Editor of Post-Medieval Archaeology charts the changes

In the two centuries after 1550, methods of manufacture in the English glass industry changed dramatically. There were three ma­ jor developments: the improve­ ment of quality associated with the French immigrant glass-makers who arrived after 1567; the change to coal as a fuel in the second decade of the 17th century; and the development of the cone-shaped furnace superstructure in the years around 1700. Over the last 20 years archaeological research has thrown new light on all three of these changes.

The traditional medieval glass was produced in two different furnaces. There was a main furnace for melting the glass, and a subsidiary furnace for annealing, a finishing process involving heating and cooling to allow internal stresses to be relieved. The characteristics of these traditional furnaces were illustrated by the excavations carried out as long ago as 1966 at Bagots Park, Staffordshire on a furnace of c.1530 (published PostMedieval Archaeology, 1967) and those at Knightons, Surrey in use up to 1550 (Eric Wood, in Surrey AC, 1982). In both, glass had been melted in furnaces of rectangular plan, but there were also subsidiary furnaces, for annealing. Only in the final phase at Knightons had there been any attempt to integrate the melting and annealing furnace structures.

Immigrant glassmakers from Lorraine and Normandy came to the Weald in the decade after 1567. This was the year when a patent of monopoly was awarded to the Antwerp glass merchant Jean Carre in an attempt to reduce the volume of imports into England. Instead of glass being imported, glass-makers were brought in. The Frenchmen used different designs of furnaces which were capable of making a glass which surpassed the traditional English product in appearance and durability.

Winbolt and Kenyon, in their pioneer fieldwork in the Weald (The Glass Industry of the Weald, 1967) realised that the French glassmakers used furnaces of a different kind, in which preparation, melting and annealing appeared to have been carried out in one complex structure: the subsidiary heating took place in the wings of the main furnace. No excavations have been carried out at Wealden sites, and it was not until the excavation of the late-16th-century furnaces at Hutton and Rosedale, North Yorkshire in 1968-71 {Post-Medieval Archaeology, 1972) that winged examples were fully examined. But, this work showed the dangers of using too simple a model of change: at Rosedale, there was a classic Lorraine-plan furnace, with triangular wings set at each corner; however, one wing had been demolished during the life of the furnace, and at some stage two separate annealing furnaces had been constructed nearby. Further, at Hutton, of the three phases of the furnace, the first two were plain rectangular structures, while the third had two rather than four wings. In addition, these excavations showed the difficulty of determining whether eroded wingstructures had contained their own fire-chambers, or had relied on heat from the main furnace fires.

Even more striking was the contrast between the glass produced by the two Yorkshire furnaces.

The glass making furnace at Rosedale. Note the two wings where the annealing of the glass was originally carried out.


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