water-glass painting

water-glass painting (also called mineral painting and stereochromy).
A method of mural painting, intended to prove resistant to the effects of damp and pollution, invented c.1825. It is essentially a variation of fresco; after the paint has been applied to the plaster, it is carefully sprayed with a solution of water-glass (potassium silicate or sodium silicate), which provides a protective film when it dries. As water-glass is strongly alkaline it can be used only with certain pigments. In the 1860s Maclise and other artists used the technique in murals in the Houses of Parliament, because it was thought that they would be proof against the damp and dirty atmosphere of London, but they deteriorated within ten years. Later the method was improved as Keim's process (developed by professor Adolf Keim of Munich in the 1880s), but because of its complexity and limitations it never became popular.