Dry-Plate Collodion

Dry-plate collodion refers to a group of nineteenth-century negative processes in which a collodion-coated glass plate is sensitized, sealed with a preservative and dried, so that it can be exposed and developed days or weeks after preparation. The processes answered the main constraint of Frederick Scott Archer's wet collodion process of 1851, which required the plate to be coated, exposed and developed while still moist, and therefore a portable darkroom on location. Jean-Marie Taupenot's collodio-albumen plate of the mid-1850s, Richard Hill Norris's gelatine-protected plates, sold commercially in Birmingham from 1858, and Major Charles Russell's tannin process of the early 1860s became the best-known methods. In 1864 W. B. Bolton and B. J. Sayce published a collodion-bromide emulsion that sensitized the plate in a single coating, and ready-made plates based on it went on sale from 1867.

Preservatives such as albumen, tannin, gelatine, honey, malt, resin and dextrin protected the dried film and kept the silver salts responsive. The price was speed. Exposures typically ran two to three times those of wet plates, often several minutes in dull light, and development could take hours. Period manuals recommended the plates for landscape, architecture, copying and still life rather than portraiture or instantaneous views, and photographers valued them for travel and mountain work, where a small camera and a box of prepared plates replaced the dark tent and silver bath. The resulting negatives, usually printed as albumen silver prints, are very difficult to tell apart from wet collodion negatives once processed. The method survives in a small revival, taught alongside wet collodion in historical-process workshops.

In most histories, "dry plate" designates the gelatin dry plate, proposed by Richard Leach Maddox in 1871 and commercially established by about 1878, whose far greater sensitivity displaced both collodion methods by the 1880s. Collodion plates nonetheless persisted in commercial and reproduction work into the early twentieth century because of their sharpness and low halation.