Reflections on glazing

by Dearbhail Keating

We travelled from Tewkesbury to Redditch to spend the day with Ben Sinclair of Norgrove Studios Ltd. Ben runs Norgrove Studios specialising in leaded stained and decorative glass design and conservation using traditional techniques. Ben has spent many years working with glass and as a result is extremely knowledgeable about the different types of glass and very experienced in identification.

The day began with analysing samples of slab, crown and cylinder glazing. These all have their own unique characteristics and place in history. The Scholars quickly appreciated how types of glass have changed over time and how identifying the glass in buildings is a useful tool in dating. Determining the type of glass is also crucial information to know before embarking on any conservation work; to replace glass insensitively can have a very detrimental effect on the aesthetic of a building.

Example of slab glass

Example of slab glass

Slab glass is one of the earliest forms of glass formed by pouring molten glass on a flat surface within a mould and is rather thick and distorted in appearance. Crown glass is formed by mouth blowing a sphere of glass, the end is then cut off and the glass spun into a disc in this curvilinear form gives it much of its character making it relatively easy to identify. Crown glass can be spun into very thin layers making it very light; it was therefore particularly popular in the first half of the 19th century when the window tax was in existence as the tax was calculated by the weight of the glass.

Example of crown glass

Example of crown glass

Cylinder glass is also formed by mouth blowing, this time in a cylinder. The ends are then cut off and the glass is fired again before it is flattened into a sheet. The glass is asymmetrical and has a beautiful varied texture by which it can be identified. By the early-20th century more uniform glass was being made, first drawn sheet glass which was formed between rollers directly from the furnace.

Examples of cylinder glass

Examples of cylinder glass

Float glass followed in the 1950s and it’s this glass that we recognise today. Following the briefing we were tasked with identifying a number of samples of glass. In the studio we observed the pain-staking task of piecing back together an intricate stained glass window. The window had been damaged due to vandalism so replacement of some glazing was necessary. To enable the repairs the entire window was removed from the church in one piece and brought to the studio allowing it to be laid out on the workbench and fully assessed. The extent of the damage meant the window could not be repaired in situ. As much of the existing glazing as possible was retained and repaired. Broken pieces of glass that could be salvaged were pieced back together by introducing an additional piece of lead. After tutorials from the experts, the Scholars had a go at glass cutting (with various degrees of success)!

Stained glass repair

Stained glass repair

We were also lucky to accompany Ben to English Antique Glass nearby glass blowing workshop where the process of making cylinder glass as well as blown glass light fittings was observed. This opportunity really gave us an appreciation of the time taken to produce traditional blown glass and to understand the whole process of glassmaking, from a bag of sand through to a sheet of glass. Thank you to all at Norgrove Studios Ltd for a great day!

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