A daguerreotype portrait of a woman reading a book, taken by an unknown French photographer in about 1850. In 1839, the Daguerreotype, invented by Louis Jacques Mande Daguerre [1787-1851], became the first photographic process to be announced to the public. A highly-polished silver surface on a copper plate was sensitised to light by exposing it to iodine fumes. After exposing the plate in a camera it was developed with mercury vapour. Daguerreotypes are unique images which may appear as a positive or negative depending on how light hits the surface.
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