DAGUERREOTYPE (dzi-g6e6-tip) PRO CESS (Fr. daguerreotype, from Dagucrre + Gk. Tiiiros, typos, impression). The original photo graphic process, as introduced by its inventor, Daguerre, in 1S39. The pictures are positive or direct, though they appear as negative when viewed at certain angles, and are the result of the successive action of the vapors of iodine, bro mine. and mercury upon a highly polished sur face of chemically pure silver. The r:anipula tions involved in conducting the process are: ( I ) Cleaning and polishing the plate; (2) ren dering the plate sensitive; (3) exposing it in the camera : (4) developing the latent image; (5) fixing the picture.
A copper plate of moderate thickness is first coated with silver by electro-plating and polished as as possible; it is then exposed first to the vapor of iodine, and then to the vapor of bromine for a length of time, ascertained in practice by watching the succession of prismatic colors which begin to appear with the first con tact of the vapor. The plate is then exposed in a camera. and the development of the latent im age, which is the next operation. is effected by
subjecting the plate to the action of the vapor of mercury, which attaches itself to the various parts of the picture in proportion as it has been acted on by the Those portions of iodide and bromide of silver unaffected by light are next removed by immersing the plate in a solu tion of hyposulphite of soda; and the picture is subsequently fixed and intensified by pouring over its surface a solution of hyposulphite of soda and chloride of gold, and applying heat; by which means it is coated with a thin film of metallic gold, and thereby rendered so perimt nent that it requires a chemical solvent for its removal. It may be mentioned in conclusion that though Daguerre published in 1839 the first imacticable process for taking pictures by the agency of light, his experiments would seem to have been suggested by the researches of Niepee, who, about 1820, obtained impressions on silver plates rendered sensitive by being coat ed with asphaltum saturated with oil of laven der. See PHOTOGRAPHY.