Photography

The next three years were required to perfect the process of heliography, as it was called, and in 1826 an etched metal plate was sent to M. Lemaitre, of Paris, to be printed. In order that the pictures should be more distinct, they were exposed to the vapors of iodine. The highlights of the plates consisted of hard ened bitumen; the shadows, of the bare metal; thus the contrasts were very poor, which led to the use of tin instead of copper. Lemaitre suggested silvering copper plates. These two facts are of importance in the subsequent history.

Daguerreotype.

In 1826, Daguerre, a painter who had ex perimented with silver salts, heard of Niepce's work and ap proached the latter as to the formation of a partnership. This was consummated in 1829. The work which Daguerre had done with Niepce had drawn their attention to the light-sensitiveness of silver iodide, and Daguerre discovered accidentally that the effect produced by exposing an iodized silver plate in a camera would result in an image if the plate were fumed with mercury vapor. The inventions of Niepce and of Daguerre were pub lished to the world simultaneously by the French Home Minister in a bill presented to the House of Deputies proposing a national reward to the inventors. A full description of their methods was presented on August 19, 1839, at a meeting of the Academy of Arts and Sciences.

The introduction of the Daguerreotype process was attended by complete success. The process required much care and skill. A silvered copper plate was buffed and burnished to a high de gree of polish. It was then iodized by careful fuming with iodine, and later (1840) resensitized with bromine, and then given an ex posure the duration of which was of vital importance. At first, exposures of minutes in bright sunlight were necessary, but later exposures were secured in a few seconds under favorable con ditions. The development was effected by placing the exposed plate over a cup of mercury heated to about 75° C. The image was then fixed with a solution of thiosulphate of soda and toned by treatment with gold chloride. The results obtained were ex cellent when all the operations had been carried out correctly, and the process flourished, especially for portraiture, until it was super seded by the wet collodion process in 1851.

Calotype.

A preliminary notice of Daguerre's success was made by Arago to the Academie des Sciences in Paris on Jan. 7, 1839. This caused Fox Talbot, an Englishman, to write to Arago claiming priority in regard to the obtaining of a picture in the camera, and having rendered it permanent. Talbot began his ex periments in 1834, using the camera obscura with silver chloride and common salt or potassium iodide as fixing agents. A com munication was made to the Royal Society of London on Jan. 30, 1839. But not until a month later did he disclose his work ing method, which then involved silver iodide with excess of the nitrate, and fixation with sodium thiosulphate. The solvent action of this for silver salts had been discovered by Sir J. W. F. Herschel in 1819. Talbot's process was called "Calotype," and the light image was developed with gallic acid, the action of which had been discovered independently by the Rev. J. B. Reade, but had not been published by him.

The developed image on a sheet of Calotype paper was the exact reverse, as far as light and shade were concerned, of the original image. Such a picture was termed by Sir J. Herschel in 1841 a "negative." Since paper is a semi-transparent substance whose transparency could be increased by waxing or oiling on the side opposite to the image, Talbot was able to obtain true copies or positives of any negative by simple contact printing upon another piece of sensitized paper. Talbot's process should be considered as the first stage in the real line of photographic development, the notable inventions of Daguerre and Niepce being merely bypaths whose chief importance was the mental stimulus they gave to photographic evolution. The disadvantages of Calotype were the somewhat long time required for printing and the structure of the paper.

Herschel suggested the use of glass plates and the deposition of silver chloride thereon. In 1848 Niepce de Saint-Victor, the nephew of Nicephore Niepce, suggested albumen as the vehicle for the sensitive silver iodide. This process, called "Niepceotype," held its own until 1851, when Scott Archer, an English architect, published his wet collodion process, which is still in use in photo mechanical establishments.