The oldest remaining manufactured glass comes from Egypt and dates from around 2000BC. Glass is formed when silicates - sand - and alkali are fused at high temperatures. The Romans made many objects from glass but the skill seems to have been neglected in Europe until about the tenth century when stained glass began to be used in church windows.

Irish early Christian churches did not have glass in the window openings. Probably they were closed by timber shutters. Irish Romanesque buildings were glazed. From then until the late Stuart periods, glass was manufactured locally in small pieces. Different metallic oxides added to the mixture gave colours to the glass. Diamond, square or round shapes were the most common form. To make a large window the pieces of glass were fitted together in narrow lead channels which were tied back by wires to iron bracing bars set across the window opening at an even spacing. The channels for the lead surrounds and the holes for the iron bars can often be seen in the window openings of ruined medieval churches in Ireland today and, since the technique has never changed, finished windows of this type of construction appear in many Gothic Revival buildings throughout the country. In domestic and public buildings, fixed lights of clear glass were common, often with hinged timber casements opening at the lower level.

In the Georgian period, technical developments made it possible to produce larger pieces of clear glass, known as Crown glass, which could be fitted directly into timber framed sash windows that gave good light to a room. The method of manufacture left the surface with a slightly curved profile that catches reflections and gives great vitality to this type of glass. From about 1830 Sheet glass, which is floated on a table, made it possible to glaze a window opening with a single piece of glass.

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