scotophor such as potassium chloride (KCl). KCl has the property that when a crystal is struck by an electron beam, that spot would change from translucent white to a dark magenta color. By backlighting such a CRT with a white or green circular fluorescent lamp, the resulting image would appear as black information against a green background or as magenta information against a white background. A benefit, aside from the semi-permanent storage of the displayed image, is that the brightness of the resultant display is only limited by the illumination source and optics. The image would be retained until erased by flooding the scotophor with a high-intensity infrared light or by electro-thermal heating. Using conventional deflection and raster formation circuitry, a bi-level image could be created on the membrane and retained even when power was removed from the CRT. By using an array of dots, say 8 × 8, a larger pixel could be formed to represent 64 gray levels. One such device, the D36 Image Display, was made by DICOMED Corporation and a technical paper was presented at the 1972 Electro-Optical Conference in Geneva, Switzerland. Patents 1962 Anderson References Pioneering Electronics (1964) The Skiatron, or Dark-Trace tube (1948) 4AP10 Skiatron data sheet IEEE transactions on Electron Devices Vol ED-14 No. 23 December 1967, "A simplified Direct-Viewing Bistable Storage Tube", R. H. Anderson Vacuum tubes Cathode ray tube Television technology