Daguerreotype

The daguerreotype is an early photographic process, and the first practical, commercially viable photographic technique, in which a direct positive image is formed on a sheet of copper plated with a thin layer of silver, polished to a mirror finish and sensitized with iodine fumes before exposure in a camera, then developed over heated mercury vapor and fixed with a salt solution. Announced publicly in Paris in 1839 by Louis Daguerre, after whom it is named, the process produced a single, unique, highly detailed image directly on the metal plate itself, with no negative and therefore no ability to make copies, and the finished plate had to be viewed at an angle to see the image clearly rather than lit flatly. The daguerreotype dominated photographic portraiture through the 1840s and into the 1850s before being displaced by processes that used a negative to produce multiple paper prints, but its extraordinarily fine resolution has never been fully matched by later nineteenth century processes.