Medieval glassworks 890m SSE of White Farm.
Reasons for Designation
Glass has been produced in England since the Roman period, although field evidence is scarce until the late medieval period. Wood was the main manufacturing fuel up to the early 17th century, so the industry was located in woodland areas, particularly the Weald. From about 1610, production shifted to the coalfields. Glass production requires three major components: silica, alkali and lime, together with colouring material for certain products and decolourisers for clear glass. Lead was also used in the production of certain types of glass during the Roman period and after the 17th century. The manufacturing process involves three stages, fritting, melting and annealing. Fritting was a common practice before the 19th century involving heating the main glass constituents to produce an unmolten material for grinding, melting and annealing. Melting involved the remelting of previously formed glass, and the production of new glass from raw materials. Until the late 19th century, glass was normally melted in pre-fired crucibles of refractory clay, on stone benches called sieges, within the melting furnace. Use of coal as the preferred fuel and automatic bottle-making machinery in the 1880s led to changes to the melting furnaces and the use of larger furnaces, hitherto conical structures over circular furnaces. Regenerative furnaces were developed in the 1860s, and tank furnaces for bulk melting quickly followed. Flat-glass production methods were made obsolete by the Pilkington float-glass system of 1959. The third process is annealing. Because the rapid cooling of molten glass can give rise to internal stresses, glass was treated in furnaces designed to heat the glass to a point where deformation begins, then cooled gradually. In the 19th century conveyors were introduced to take glass through a hot zone into cool air. Features on glass manufacturing sites include various types of furnaces, producer-gas plants for the making of gas from coke at 19th century glassworks, bottle-making machinery, blowing irons or pipes for blowing glass, glass residues and various buildings used as stores or warehouses. A total of 135 glass production sites (representing about 25% of the estimated national archaeological resource for the industry) have been identified as being of national importance. This selection, compiled and assessed though a comprehensive national survey of the glass industry, is designed to represent the industry's chronological depth, technological breadth and regional diversity, and to include all the better preserved glass sites, together with rare individual component features.
The medieval glassworks 890m SSE of White Farm is a good survival of this rare monument class with structural and archaeological remains and deposits which will provide information on the construction and practice of glass working during the medieval period.
This record was the subject of a minor enhancement on 3 July 2015. The record has been generated from an "old county number" (OCN) scheduling record. These are monuments that were not reviewed under the Monuments Protection Programme and are some of our oldest designation records.
The monument includes the remains of a medieval glassworks within Bishop’s Wood. The glasswork site includes the remains of a rectangular glasshouse and is built from sandstone and glacial erratic boulders on a raised plinth. It includes the remains of a furnace with a central flue and 4 internal crucibles and an adjacent working area. The monument was excavated in 1931-32 and restoration was carried out in 1933 when a wooden shed was erected over it (which no longer remains). The glassworks were in use from 1580 when Bishop Overton brought glass workers with him from Hampshire until 1615 when legislation was passed which prohibited the use of wood in the manufacture of glass.