COLORED GLASS is made ordinarily like any others, by the addition of dyes (generally metal oxides) to the molten charge. The same metal produces several colors at different temperatures. Iron gives all the rainbow hues in the order of their position in the spectrum, but its common est effects are green and orange. Manganese, so staple a decolorizer as to have earned the name `glass-makers' soap,' produces in excess pink or amethyst. The manganese in old window-glass frequently is betrayed by the analysis of long sunlight in the purple tints that appear. Too high a temperature turns it brown, then yellow, and finally green. Copper makes the reds of cheap glass, and when heated further turns purple, blue, and green. Cobalt gives rich blue or black. Gold, in the form of 'purple of Cassius,' and in a simple solution, creates the finest rubies, violets, and amber, one part of the precious metal coloring a thousand parts of glass. The exquisite objects of amber glass which shade into red are colored from a gold solution in the cru cible, and after being fashioned into the desired shape are held in the `glory-hole' a few minutes. The second heat transforms the amber to red and the unheated portion remains an' amber tint.
Silver gives a beautiful yellow, and uranium, green or yellow. Carbon, in powdered coal, is used for cheap black and amber bottles. Opa lescent ware, in which modern fancy glass excels, gets its color from cryolite, arsenic, or tin.
Mosaic window-glass is cast like rough plate glass from small ladles, and the desired tints are carefully selected, to be patched together in harmonious designs by leaden joints. See WIN DOW.
Painted glass is colored by enamels fused to the surface. Stained glass is produced by soluble metal oxides applied with a brush and fastened in the stainer's kiln. 'Flashed glass,' or double glass, is made by coating the embryonic bulb of transparent glass with a dip of colored glass and blowing both as one into a sheet of window-glass, a lantern-globe, or whatever shape is desired. Opaline glass for art windows is made by pouring colored glass of one or more kinds upon white opaque glass and then pressing the whole with a heavy iron roller. This causes the different glasses to intermingle, affording great varieties of color effect. See STAINED GLASS.