Cathedral glass is the name given commercially to monochromatic sheet glass, which is thin by comparison with slab glass, may be coloured and is textured on one side.
The name draws from the fact that windows of stained glass were a feature of medieval European cathedrals from the 10th century onwards.
The term cathedral glass is sometimes applied erroneously to the windows of cathedrals as an alternative to the term stained glass. Stained glass is the material and the art form of making coloured windows of elaborate or pictorial design.
Most early stained glass was made by mouth-blowing long cylinders of molten glass, which were partly cooled, had the ends removed, were cut open, reheated and flattened.
A second technique that was employed was to pour the molten glass onto a metal table top. The upper surface was smooth and glossy but the lower surface produced an irregular knobbly patterning caused by the way in which the glass reacted with the cold metal surface. The knobbles have the appearance of having been hammered flat.
In the modern glass manufacturing and trading process, it is glass that has the characteristics of the latter that is referred to as cathedral glass.
Modern cathedral glass may superficially resemble table-poured glass but close examination may show a regularity in the texture and a dullness of surface that indicate it has been moulded. It is usually machine made, much of it being manufactured in China.
In England and Germany some cathedral glass is still manufactured by more traditional table-poured means by companies which specialise in the production of glass for restoration purposes and which also make cylinder glass.
Cathedral glass comes in a very wide variety of colours and surface textures including hammered, rippled, seedy, and marine textures.
Cathedral glass was also used extensively throughout the 20th century in non-pictorial windows in churches where it was an inexpensive alternative to stained glass, yet created a pleasant ambiance because of the filtered light and colour.
The major modern use for cathedral glass is in the glazing of bathroom and toilet windows and panels in front doors in order to let in light but reduce visibility.
Much of the more brightly-coloured cathedral glass is sold in small sheets measuring 12x12 inches to hobbyists and commercial manufacturers of small lead light and stained glass objects, such as table lamps.
It is also used for the creation of modern stained glass windows in which the texture of the glass is treated, with the colour, as a significant design element.