Wet plate

The collodion process is an early photographic process.

Collodion process, mostly synonymous with the "collodion wet plate process", requires the photographic material to be coated, sensitized, exposed and developed within the span of about fifteen minutes, necessitating a portable darkroom for use in the field. Collodion is normally used in its wet form, but can also be used in humid ("preserved") or dry form, at the cost of greatly increased exposure time. The latter made the dry form unsuitable for the usual portraiture work of most professional photographers of the 19th century. The use of the dry form was therefore mostly confined to landscape photography and other special applications where minutes-long exposure times were tolerable.

The collodion process is said to have been invented in 1851, almost simultaneously, by Frederick Scott Archer and Gustave Le Gray. During the subsequent decades, many photographers and experimenters refined or varied the process. By the end of the 1850s it had almost entirely replaced the first practical photographic process, the daguerreotype.

During the 1880s the collodion process, was largely replaced by gelatin dry plates—glass plates with a photographic emulsion of silver halides suspended in gelatin. The dry gelatin emulsion was not only more convenient but could be made much more sensitive, greatly reducing exposure times.

One collodion process, the tintype, was in limited use for casual portraiture by some itinerant and amusement park photographers as late as the 1930s, and the wet plate collodion process was still in use in the printing industry in the 1960s for line and tone work (mostly printed material involving black type against a white background) as for large work it was much cheaper than gelatin film.

The wet plate collodion process has undergone a revival as an historical technique over the past few decades. There are several practising ambrotypists and tintypists who regularly set up and do images at Civil War re-enactments. Fine art photographers use the process and its handcrafted individuality for gallery showings and personal work. There are several ISTmakers of reproduction equipment exist. The process is taught in workshops around the world and several workbooks and manuals are in print. Many artists work with collodion around the globe, including Kurt Grüng, Sally Mann, and Ben Cauchi.

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