The skiatron is a type of cathode ray tube (CRT) that replaces the conventional phosphor with some type of scotophor, typically potassium chloride. When hit by the electron beam from the back of the CRT, this normally white material turns a magenta color, producing a dark spot or line on the display. The pattern remains on the display until erased by heating the potassium chloride layer. Skiatrons were used as an early form of projection television display, particularly in radar stations during World War II. These tubes are also sometimes known as dark trace CRTs or dark trace tubes.