Glass offers more than meets the eye, says David Winpenny
A large sigh of relief was heard over York last week when the Minster’s great east window, in storage for repairs, was saved from a fire that broke out directly above it. The loss of this major work of art would have been appalling – yet it is made of something so fragile that we must be immensely grateful that it has lasted for almost exactly 600 years; the glazing was completed in 1408.
Glass is a very special material. It is made of very basic resources – quartz sand, soda and lime at its most basic – which are heated. It was discovered, according to the Roman historian Pliny, by Phoenician merchants around 5000 BC. We have ancient Egyptian glass, and Roman glass frequently turns up in excavations all over Britain – there are some good examples in the museum at Aldborough near Boroughbridge.
Given that it is both brittle and very long-lasting, we should take more notice of it. The ability to make glass in different ways over the centuries has a remarkable influence on architecture. From its earliest days as a building material, glass was expensive. This had two effects. The first was that glass was bought only by the very wealthy (which could include the Church); the second was that early glass windows were very small. Some of the world’s earliest stained glass is in the church at Jarrow on Tyneside; the windows in the Anglo-Saxon building that it glazed are tiny – perhaps 18 inches high by 10 wide.
It is hard to know how larger openings, like the round-headed ones in the Norman parts of Ripon cathedral, were covered – if at all. Sometimes small pieces of horn would be placed in a window frame – but a place the size of the cathedral would need the sacrifice of an awful lot of cows or stags. It is more likely that the openings were not covered – which is why they are all at a high level in the building.
Between the 11th and 13th centuries glass-masters in Germany and Venice developed techniques for making comparatively large pieces of glass. In one they blew a sphere of molten glass then spun it into a disc, a yard or more wide, from which panes could be cut. Making this ‘crown glass’ left behind the central ‘bulls-eye’ where the glass was attached to the blowing rod; the bulls-eyes were popular in the 20th-century for imparting an ‘olde-worlde’ flavour to a building. There are several modern copies on the window of Tom Crudd’s Bar in the Unicorn Hotel.
Another technique was to make ‘muff glass’ – a cylinder up to 10 feet long was blown, then split and flattened. Both crown glass and muff glass left tell-tale streaks and sometimes air bubbles in the glass; if you look closely at old glass it is usually possible to see them, and sometimes you can work out which technique was used. The streaks in crown glass curve (the more pronounced the curve, the nearer to the centre of the disc was the origin of the piece of glass), while in muff glass they are straighter.
Neither crown nor muff glass could be made in very large pieces, so the panes had to be leaded together, whether for stained or for clear glass – and the larger the window, the more you proclaimed your wealth – the rich Bess of Hardwick showed off at Hardwick Hall in Derbyshire with a house that was ‘more glass than wall’, for example. By the 18th-century wooden frames had replaced the leading, but the panes were still small, hence the typical multi-paned Georgian sash windows.
Plate glass had already been invented by the French in 1688 but it was mainly used for mirrors rather than windows. Only in the middle of the 19th century did glass manufacture stop being a craft and move to being an industrial process. Steel pioneer Henry Bessemer invented rolled glass – passing a continuous ribbon of glass between rollers to produce larger sheets – but it was still not cheap, as the resultant glass needed special polishing. Similar polishing was needed for another technique, casting large sheets on an iron surface. This is probably how much of the glass in Ripon’s 19th-century shop windows was cast – including the curved panes on some premises.
It was as late as 1960 that float glass was made in commercial quantities, by producing a continuous ribbon of glass floating on molten tin. This transformed architecture – huge plates of glass replaced walls, and shops boasted ever-larger windows – the results are all around us, including in the new development west of the Market Square.
But there is a danger. Float glass is so perfect it can rob buildings of their character. If you replace earlier glass with it you lose the unexpected reflections and quirks that provide interest. One piece of glass is not like another, so if a window needs reglazing – especially within a Conservation Area like the centre of Ripon, consideration should be given to replacing like with like. Earlier types of glass are still made and are easily available. Clearly, we should see our way to using them where appropriate.
• Have you completed the ‘Horns’ Christmas Quiz? Today (8 January) is the closing date, so make sure they are with the Gazette by 5.00 pm. The answers and the name of the winner will be in next week’s Gazette.
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