A daguerreotype portrait of a young woman, taken at the studio of Rufus Anson, Broadway, New York in about 1860. This is one of a pair of portraits showing the same woman at different ages. In 1839, the Daguerreotype, invented by Louis Jacques Mande Daguerre [1787-1851], became the first photographic process to be announced to the public. Daguerreotypes are unique images which may appear positive or negative, depending on how light hits the surface. 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.
© Royal Photographic Society/National Museum of Science & Media/Science & Society Picture Library