ColorAcademy 2005

Glass

Glass is a manufactured thermoplastic consisting commonly of silicates of calcium and sodium, composed of silica, lime and potash or soda. Traces of metal oxides are used to colour the glass or to modify unwanted coloration. Opacity, transparency or translucency (opalescence) are determined by the relative proportions of the raw ingredients, which form glass after three or four hours smelting at a temperature in excess of 1,500 degrees Celsius.

To stain glass, metal oxides are either added to molten glass during smelting, to obtain so-called pot-metal glass, or suspended in a gum solution and painted on to the glass before refiring, which fuses a coated stain to its surface.

By 1100 the master glaziers of France were the leading exponents of the art and windows at Le Mans, Bourges and Chartres testify to the great Gothic age of stained glass in Europe.

Glass is coloured in its manufacture by the addition of a wide variety of mineral compounds, each of which fuses with the raw materials of the glass to yield a characteristic colour. Oxides of cadmium, selenium or iron produce red glass, and those of cerium, titanium or vanadium give various yellows; oxides of nickel, chromium or tellurium give greens, and copper oxide gives either green or blue glass.
Cobalt oxide is the blue colouring agent of the famous Venetian sìmutanè and Bristol Blue glassware of the seventeenth and eighteenth centuries. Manganese slicates give purple or brown glass, and may be used to deepen many of the above colourations.

Stained Glass Windows can be used to create beautiful effects as in this image here, photographed in the National Cathederal, Washington DC.

Stannic (tin) additives give translucent white or opaline glass.
Vireous enamel consists of glass powder compounded so as to be able to fuse permanently to a metal surface, as that of copper, gold, silver, steel or aluminium, at a temperature of about 650 degrees Celsius. It is inlaid either into chiselled cavities, known as champleve work, or between soldered partitions, known as cloisonne work.
In De la Loi du constrast simultane des couleurs (1839), Michel-Eugène Chevreul , in admiring the beauty of colour in stained glass windows, observed how outlines contributed 'to render the impression of colours stronger and more agreeable'. In the conventional type of stained glass window, the strips of leading between each glass fragment, in addition to locking the window panes together physically, ensure minimum 'colour spreading' of the enclosed colours. In stained glass, it is often the blue that appears to spread its colour most. In a style of painting called Cloisonism, from its resemblance to partitioned enamelwork, a group of French painters influenced by Paul Gauguin (1848-1903) composed pictures in which areas of saturated colour were bounded by dark outlines. Black outlines were a characteristic of the work of Fernand Lèger (1881-1955) and in his later years, he extended his painting style into the medium of stained glass, including designs for windows at the Church of Sacré-Coeur at Audincourt in France (1951-52). George Rouault (1871-1958), a French artist who had been apprenticed to a stained glass painter, similarly produced designs later in life, as for the Church of Nôtre-Dame de Toute Grace (1945).