190,218. British Thomson - Houston Co., Ltd., (General Electric Co.). Sept. 12, 1921. Gilding and silvering. -A metallic film is de posited on the inner surface of a bulb for use as a photo-electric discharge device, by securing a bead of gold or silver on a filament 6 of refractory material such as tungsten, molybdenum or tantalum, and heating the filament by passage of current to volatilize the metal of the head, the condensation of which on the bulb may be assisted by cooling the bulb, for instance, by immersion in water; the pressure in the bulb is maintained at 5 microns during the process. Moisture is removed by heating the bulb to 360‹ C. and exhausting through a tube 9. A nickel shield 7 of conical or other shape prevents deposition of the metal on a part 12 of the bulb, and a shield 8 prevents deposition on the side tube 2.