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Window of opportunity The National Glass Centre in Sunderland has become a new source of hand-made coloured glass

technical & practice

Many new buildings now include commissions for works of art. Glass, particularly, offers the chance to integrate art with the fabric of the building, as part of the same expression.

In the recent past, the supply of coloured window glass has been a little erratic. Some poor-quality coloured sheet glass has been imported from Poland and some better hand-made glass from France. But fine English hand- made glass has been out of production. Now, a new company, Sunderland Glassworks, has revived the production of fine hand-made flat glass.

The National Glass Centre, opened in June 1998, contains a museum, a factory, some small studios, a shop which sells the products of studio glassmakers from all over the country, and the public can watch glass- making in progress. With all these facilities, the centre has greatly raised the profile of studio glass.

The Sunderland area has long been a centre for glass-making. A long-established firm there, Hartley Wood, used to be the monopoly supplier of hand-made flat glass. Hartley Wood was to have moved into the National Glass Centre but, six months before it was due to move, its owner, a Hong Kong businessman, closed it down. Other established firms - such as Caithness and Dartington - were unwilling to move or expand into the Centre. So Mike Willshare, a Sunderland businessman with a background in the glass industry, set up Sunderland Glassworks Ltd to make glass in the National Glass Centre.

Glass-making

Glass requires a manufacturing temperature of about 1350degreesC (higher than most pottery-making) and about 1200degreesC for working it. So it can really only be produced by a workshop which is large enough to run kilns day and night with a group of people producing vessels on a continuous basis. It is hard work; the furnace is so hot that the tools have to be constantly cooled with water.

There are basically two ways of forming glass: flat glass and blown vessels. Flat glass for windows is now mostly made by the float process (aj 6.6.96 p47). Blown-vessel making is a craft method, used in Sunderland. The way of working, established in antiquity, is essentially unchanged. From a pot of molten glass in a kiln, a lump of hot glass is withdrawn on the end of a blowing iron - a long steel tube. Blowing through this tube forms a bubble of glass, ready to become a bottle or vase.

There are many techniques for its detailed glass-forming. In particular, the clear glass bubble can be dipped in molten coloured glass (called flashing) or rolled in powdered coloured glass in a tray. The coloured glass tends to be very strongly coloured so it is advantageous to use it fairly thin. This is easily done by blowing the clear glass bubble larger after coating it with coloured glass.

Sunderland Glassworks also makes glass vessels - bowls and vases - as giftware, along with decorative glass paperweights. Flat glass is derived from the same process of blowing vessels, so they all depend on the company being able to maintain a substantial group of skilled glass blowers serviced by fair-sized kilns.

To make a sheet of flat glass by this method, a very large bubble is blown from a lump of glass, a 'gather', of about 8kg. This requires a very strong, highly skilled glass blower. The bubble is blown and rolled in a trough until it is about 300mm in diameter and about 600mm long. Then the ends are cut off. It is split down one side and flattened out in a special kiln. The result is a sheet about 900 x 600mm.

Many colours are available. The glass is streaky, of varied hue, with perhaps a few bubbles in it. When used in a window it glows with a jewel- like radiance worlds away from ordinary coloured sheet glass.

Sunderland Glassworks is now in full production of flat coloured glass, having only got the process running reliably just before Easter. The entire range of glass, in about 150 colours, is stocked and distributed by a T&W Ide subsidiary, James Hetley, in London. Each piece is individually priced; it is of the order of £115/m2.

Making windows

There are two main forms of coloured glass windows: leaded lights and resin-bedded. Leaded lights are still produced in the traditional way by firms such as The Art of Glass in Birmingham, which makes both traditional and secular windows as well as restoring old windows. On a full-sized design, the pieces of glass are cut to shape freehand and assembled in position. H-section lead 'cames' fill the gaps and hold it all together. New windows cost around £1000/m2 in hand-made glass, down to half that in machine-made glass. In fact glass from many sources is often mixed in a single design.

There is only one actual stain, a yellow, so 'stained glass' is strictly a misnomer. Detail is painted on in enamel colours and fired. The trade association is the Society of Master Glass Painters, which has about 40 associate members producing new designs. It also accredits about 30 studios for conservation work. (Perspectives magazine did a survey of stained glass makers in September 1995, p 60-63.)

The second way of making coloured windows is resin-bedding. On a sheet of toughened or laminated glass, pieces of coloured glass are assembled on clear resin. This method does away with the lead cames. And the base sheet of glass can be assembled into a double-glazed unit, making the coloured sheet suitable for glazing into a window in the normal way. The smooth surface on both sides of the double-glazed unit eases any cleaning problem.

Such windows can be very large if required. The relative ease of making and fitting them has made them very popular. They can incorporate many elements, such as rods of glass and etched and sandblasted pieces, and can be either fitted to the shell of the building in the normal way or used as internal screens. The opportunities for the glass artist have never been wider. They are there for architects to make use of.

John Rawson is an architect and writer

Sunderland Glass Works, tel 0191 515 5511, fax 0191 515 552.

National Glass Centre, tel 0191 515 5555, fax 0191 515 5566.

James Hetley Ltd, tel 0171 780 2345, fax 0171 790 2682.

The Art of Glass Ltd, tel 01564 703992, fax 01564 700057.

Society of Master Glass Painters:

http://www.bsmgp.org.uk

e-mail: sec@bsmgp.org.uk

Contemporary Stained Glass: A Guide to the Potential of Modern Stained Glass in Architecture. Andrew Moor. Mitchell Beazley. 1989, reprinted 1998. £16.99.

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