IRIDESCENT GLASS (from Lat. iris. Gk. Ipts, iris, rainbow). Glass containing a display of changing colors on the surface somewhat sim ilar to the delicate hues of soap-bubbles. It is produced by rendering the surface of the glass imperceptibly uneven. either by artificial means or by the natural process of incrustation and decay. One form of treatment consists in ap plying to the surface of the glass to he treated a strong solution of hydrochloric acid under pressure in a closed vessel. Another method in use in many factories is to apply the fumes from chloride of tin or other chlorides volatilized in a reheating furnace. Glass which has for many years been submitted to the slowly disintegrat ing influences of natural causes, such as damp. successive heat and cold. light and darkness, will in many instances display an iridescent play of colors. The cause is due to a process of decom position in the texture of the glass, resulting in the formation of minute scales. The action of water on glass has a tendency to extract the potash and soda which enter into its composition, together with a portion of the silica, the decom position taking place with greater ease in pro portion as the glass is richer in these alkalies, and more minutely divided, and the temperature of the water higher. The moisture in the
atmosphere produces a similar alteration in the lapse of time. It separates the potash and soda, leaving the greater part of the silica with the lime on the surface of the glass. It is this decomposition which causes the prismatic colors. If subjected to heat, numerous fine scales will peel off and leave the surface dull, opaque. and wrinkled. Many attempts have been made to imitate by artificial means the singular display of changing hues, and varied success has attended the efforts. In Venice the workers succeeded in giving the surface of their glassware a peculiar kind of metallic iridescence, and a similar result was reached by certain Hungarian glass-workers. The beautiful Farrile Glass made by Tiffany of New York has a most striking iridescent play of color.. Sce GLAss.