Pot-metal glass

Refers to a type of glass characterized by being one deep color throughout its thickness. The process by which it is made is ancient, and requires the combination of silica, potash, and lime, with metal oxides added to the molten glass for color. The name refers to the metal oxides and the custom of melting the compound in a clay pot in the furnace. This type of glass was generally used in making stained-glass windows, with the typical effect of relatively little light penetrating the deep, saturated colors of the glass. A technique was later developed to create "flashed glass," which layers color over clear or white glass and allows more light to pass through the window.