English inventor of the first practical photographic process by which more than one copy of a picture could be made.

Archer, a butcher's son, began his professional career as an apprentice silversmith in London, then turned to portrait sculpture. To assist him in this work, he began experimenting with the calotype photographic process of William Henry Fox Talbot (Talbot, William Henry Fox). In 1851 he described his wet collodion process, by which finely detailed glass negatives were produced; from these, paper positives could be printed. The plates had to be developed before the sensitized collodion dried after exposure, so that a darkroom tent and portable laboratory were needed for outdoor photography; but the new process produced such good results that it dominated photography for a generation. A lawsuit by Talbot claiming that the wet collodion was merely a variant of his own process was dismissed.

Archer also invented the ambrotype, a cheap form of portraiture, in collaboration with another photographer, but, having devoted all his funds to research, he died in poverty.