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By the 1850's both the Daguerre and Talbot processes were replaced by the wet plate process resulting from discoveries by Frederick Scott Archer in 1851. With this process, negatives were produced on glass plates and required shorter exposures than previous methods. The negatives could be placed against a black background to produce a direct positive photograph (collodion positives or ambrotypes) or used to make albumen prints. Albumen paper, introduced by Blanquart-Evrard in 1850, was made by coating paper with albumen from egg whites containing salt sensitized with silver salts. The collodion wet plates had to be exposed and developed while the plates were wet, before the surface hardened. This greatly restricted the mobility of the photographer, requiring considerable supportive supplies and equipment to be carried along with the camera. Literally, a mobile darkroom was essential. |
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