Glass that has been given translucent colour in any of various ways, used particularly for creating pictorial designs in church windows. Although the term ‘stained glass’ is hallowed by long usage, much window glass could more strictly be described as ‘coloured’ (when it is dyed in its substance) or ‘painted’ (when pigments are applied to its surface). Colour was usually created by adding various metallic oxides to glass at the molten stage (copper for red, for example, and cobalt for blue). Such glass that is dyed one colour throughout its thickness is known as pot glass or pot metal. Details—such as facial features—were added by black pigment, which was fixed to the surface by means of a light firing. True ‘staining’ was introduced in the 14th century and was achieved by applying silver salts to white glass and firing it in a kiln; this produced a yellow colour, and orange could be obtained by repeating the process.
In its most characteristic development and its highest achievements stained glass is essentially an art of Western Christendom, practised most splendidly in the west and north of Europe as an adjunct to Gothic architecture. Its early history is obscure, and the first surviving complete windows—in Augsburg Cathedral and datable c.1050–1150—show an art already nearly perfect in technique. Medieval windows are generally made up of hundreds of small pieces of glass of varied colours and shapes held together by strips of lead—somewhat like a jigsaw puzzle with dark outlines around the pieces. Windows of any size were made up of several panels so treated, and these were set in a framework of iron (‘armature’) that served not only as a support against wind pressure, but also to accentuate the main lines of the design of the window. The period from roughly 1150 to 1250 was the greatest age of stained glass: colours were strong and rich; designs were bold and fresh; and the feelings conveyed were lofty and awe-inspiring. From the 15th century, stained glass tended towards a greater pictorialism, imitating the effects of oil painting, and this trend reached its height in the 18th century, when some artists painted on glass more or less as they would on canvas. With the Gothic Revival in the 19th century there came a return to medieval principles, and William Morris and his associates (notably Burne-Jones) were among the foremost designers in this spirit. In the 20th century many noteworthy artists have designed stained-glass windows, in both figurative and abstract veins—among them Chagall, Matisse, and Piper.