DAGUERRE OTYPE PROCESS, the name given to the original photographic process, as introduced by its inventor, M. Daguerre, in 1839. Notwithstanding that it has now become so unpopular, on account of the very circumstance which gives such perfection to the result—viz., the polish of the plate—it is a process which yields to none in point of microscopic perfection of detail and perfect gradation of shade. The pictures it yields are positive or direct, as given in the camera, though they also appear as negative when viewed at c2rtain angles, and are the result of the successive action of the vapors of iodine, bromine, and mercury upon a highly polished surface of chemically pure sil ver. The manipulations involved in conducting the process are-1. Cleaning and pol ishing the plate; 2. Rendering the plate sensitive; 8. Exposing it in the camera; 4. Developing the latent image; 5. Fixing the picture.
A copper plate of moderate thickness is coated with silver by the electrotype or other suitable method, and then polished to the utmost possible extent, so as to obtain, though by mechanical means, a chemically pure surface; 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 beautiful succession of prismatic colors which begin to appear with the first contact of the vapor. The length of exposure in the camera which follows is deter
ndned by the amount of light at the time of operating, and the relation between the diameter and focal length of the lens employed. The development of the latent image, which is the next operation, is effected by exposing the plate in a suitable box to the vapor of mercury, which attaches itself to the various parts of the picture in proportion to the more or less intense action of the light. Those portions of iodide and bromide of silver unacted on by light, are next removed by immersing the plate in a solution of hyposulphite of soda; and the picture is subsequently fixed and intensified by pouring over its surface a solution of hyposulphite of gold, and applying heat; by which means it is coated with a thin film of metallic gold,•and thereby rendered so permanent that it cannot be rubbed out by ordinary means, but requires a chemical solvent for its removal. It may be mentioned, in conclusion, that though M. Daguerre published, in 1839, the first p•actleab!e process for taking pictures by the agency of light, his experiments would seem to have been suggested by the researches of M. Niepce, who, in 1820. obtained impressions on silver ptates rendered sensitive by exposure to the vapors of sulphur and phosphorus.