What is "collodion process"

Collodion \Col*lo"di*on\, n. [Gr. ? like glue; ko`lla glue + ? form. Cf. Colloid.] (Chem.) A solution of pyroxylin (soluble gun cotton) in ether containing a varying proportion of alcohol. It is strongly adhesive, and is used by surgeons as a coating for wounds; but its chief application is as a vehicle for the sensitive film in photography.

Collodion process (Photog.), a process in which a film of sensitized collodion is used in preparing the plate for taking a picture.

Styptic collodion, collodion containing an astringent, as tannin.

The collodion process is an early photographic process, said to have been invented, almost simultaneously, by Frederick Scott Archer and Gustave Le Gray in about 1851. During the subsequent decades of its popularity, 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.

"Collodion process" is usually taken to be synonymous with the "collodion wet plate process", an intricate process which required 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. Although collodion was normally used in this wet form, the material could also be used in humid ("preserved") or dry form, but at the cost of greatly increased exposure time, making these forms unsuitable for the usual work of most professional photographers—portraiture. Their use was therefore confined to landscape photography and other special applications where minutes-long exposure times were tolerable.

During the 1880s the collodion process, in turn, 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 still 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.