Glass artefacts from Jesus College, Cambridgeshire

grozed quarry
Grozed glass piece

Nothing indicated wealth and comfort in medieval England more than beautifully glazed windows. Continuing work on the finds coming out of excavations at Jesus College, Cambridge, has identified moderate amounts of post-medieval glass, most commonly pieces from discarded bottles. Amongst the earliest pieces of glass, however, are two fragments of attractive medieval window .

Likely to date to the 13th century, the first fragment is decorated with a red/brown painted border, while the second has been grozed, or ‘nibbled’ along its outer edges, creating a characteristic diamond shape. Grozing irons were used for this cutting process on medieval window glass until the diamond cutter was introduced in the 15th century.

painted window glass
Painted glass fragment

The two fragments are both of a type of glass sometimes referred to as ‘forest glass’ because the small glasshouses that produced it were usually situated in woodland; woods were an ideal location for glass manufacture as large quantities of wood were required as fuel to fire the furnaces, and wood ash was needed as a flux in glass production. Although both fragments now appear opaque due to weathering, they would originally have been translucent.

While the Jesus College glass may have been produced in the 13th century, it is possible that it was recycled in windows of a later date.  It is not uncommon to find early glass re-used in later buildings for political and ideological reasons, or to assert the antiquity of a building. Following the Dissolution of the monasteries in the 16th century, glass may have been resold or appropriated. Second-hand glass from wealthy religious establishments may have been a good buy for secular homes owned by those with money and influence.

Ruth Beveridge

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