Daguerreotypes

The daguerreotype is an early type of photograph, but, unlike modern photographs, it has no negative. more...

Instead, it is an image exposed directly onto a mirror-polished surface of silver, which has first been exposed to iodine vapour, and also in the later use of the process, bromine vapour, housed in a velvet-lined folding case. While the daguerreotype was not the first photographic process to be developed, images of earlier processes required hours of exposure. The daguerreotype photographic process was one of the first to permanently record and affix an image with exposure time compatible with portrait photography, and became the first commercially used photographic process.

The daguerreotype is named after one of its inventors, French artist and chemist Louis J.M. Daguerre, who announced its perfection in 1839 after years of research and collaboration with Joseph Nicephore Niepce (the French Academy of Sciences announced the process on January 9 of that year).

Daguerre's French patent was acquired by the French Government. On August 19, 1839 the French Government announced the invention a gift "Free to the World." Nearly simultaneously in England Miles Berry, acting on Daguerre's behalf, had obtained a patent for the daguerreotype process on August 14, 1839.

The daguerreotype was a positive-only process allowing no reproduction of the picture. The pre-exposure preparation of the plate resulted in the formation of photo-sensitive silver halide; and exposure to light formed a latent image. The development of the visible image was then effected by placing the exposed plate over a slightly heated (about 75°C) cup of mercury. The vapour of mercury condensed on those places where the light had acted in an almost exact ratio to the intensity of its action. This produced a picture in an amalgam, the vapour of which attached itself to the altered silver iodide. Proof that such was the case was subsequently afforded by the fact that the mercurial image could be removed by heat. The developing box was so constructed that it was possible to examine the picture through a yellow glass window whilst the image was being brought out. The next operation was to fix the picture by dipping it in a solution of hyposulphite of soda. The image produced by this method is so delicate that it will not bear the slightest handling, and has to be protected from being accidentally touched. Additional experimentation found that treating the plate with heated gold chloride would tone and strengthen the image, though it was still quite delicate and required a well sealed case to protect against touch as well as oxidation of the finely polished silver, which formed the blacks in the image.

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