© Royal Photographic Society/National Media Museum/Science & Society Picture Library
A daguerreotype photograph of a posed tableau of a woman bringing food to a wounded soldier, taken by an unknown photographer. Dated October 20 1842. 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.