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Stained Glass

Glass is made from pure silica sand, combined with lime and soda. The purer the sand the clearer the glass. Glass with impurities such as iron or magnesium will discolour or become opaque. Glass is brittle with a low tensile strength, so it cannot be used in construction. Its earliest use was confined to decorative mosaics, but in the Middle Ages glass was used in the windows of the major churches.

By the C17, glass was blown into cylindrical shapes and then flattened out and cut into shapes to be set within a lead framework which was the inserted into a metal or wooden frame. CrownGlossary Term glass was blown and spun in large circular discs up to 5ft in size with an untainted brilliant surface but with distortions in the glass. Sheet glass appeared in 1838. Thinner than plateGlossary Term glass and considerably cheaper it could be produced to large dimensions.

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Manchester, Daily Express Building, Great Ancoats Street

From the 1880s to 1950 industrial processes were applied to large-scale plateGlossary Term glass manufacture. To a limited extent this made it possible for plateGlossary Term glass panels to be used to clad steel frame buildings.

In 1959 Pilkington Glass pioneered float glass, produced by floating the molten glass across liquid tin. This combined the lack of distortion of plateGlossary Term glass with the high finish of sheet glass. Its perfect smooth surface made it possible to create glass curtain walls, attached to but separate from the framework of modern buildings. Glass window mullions and clear adhesives gave the appearance of transparency. Since the 1980s glass panels have been entirely separated from any framework to create true curtain walls secured by cables.

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British Museum

Glass has also provided the means to roof buildings and not only protecting the interior from the weather but also lighting it. A notable recent example is the roof of the Great Court at the British Museum.