Wet-collodion

Group portrait of Inuit girls and women, 1854. The photographer, Capt. Inglefield, saw the collodion process at the Great Exhibition of 1851, and had a copy of Archer's 1852 Manual of the Collodion Photographic Process. Print from a wet-plate collodion negative in the collection of the National Maritime Museum. image by Captain Edward Augustus Inglefield (Image rights)

Wet-plate camera by J.J. Pyne of Manchester, with brass lens made by Charles Louis Chevalier image by Roman Art (Image rights)

The Wet-Collodion (or wet-plate collodion) process is an early negative-positive photographic process. It was invented in 1850, and published in 1851 by Frederick Scott Archer, although a Frenchman, Gustave Le Gray may have discovered the process at around the same time.

The process uses potassium iodide dissolved with collodion - a solution of gun-cotton in ether. Gun-cotton is made by treating cotton wool (almost pure cellulose) with nitric acid, producing nitro-cellulose. Nitro-cellulose was later used as a flexible base material for film; in the wet collodion process however, it does the same job that gelatine does in modern film; it contains the light-sensitive material, in a layer permeable to chemical solutions.

The potassium iodide/collodion solution is spread onto glass plates, after which the ether evaporates. Before the ether completely evaporates, the plates are sensitized in a bath of silver nitrate solution. The plate had to be loaded into a dark slide and exposed while still wet, so the plate preparation had to be done immediately before use (once dry, the collodion would not be permeable to the developing solution). This meant that outside the studio, photographers had to carry a small tent with a supply of plates, sensitization bath and bottles of the solutions.

The collodion process was used in other forms beside the glass negative plate:

• Ambrotypes are direct positive images made by the wet collodion method on glass plates, using the reflective property of the developed silver image.
• Ferrotypes (also called tintypes or melanotypes) are direct positive images made in the same way, but on black enamelled iron plates, which were cheaper, lighter and more robust than glass plates.

Some of the silver nitrate solution would drain from the plate in the camera: Edward Estabrooke (1903) in a manual for the ferrotype process, recommended treating new wooden plate holders by immersing them in boiling oil, or soaking it with melted paraffin wax, to protect the wood from the solution, and applying shellac varnish, weekly if the holders are used continuously.

However, the process was popular, in part because the plates were considerably more sensitive than other existing media, allowing shorter exposure times, which in particular made portrait photography more convenient.

Links

• Wet Plate Collodion Forum
• Collodion Process on Wikipedia
• Getting Started in Wetplate Collodion Photography by Joseph Smigiel on Unblinking Eye.
• Lewis Carroll's wet-collodion outfit and a portable sensitizing tank for collodion plates in the catalogue of an exhibition Cameras: the Technology of Photographic Imaging at Museum of the History of Science, Oxford 20 May - 13 September 1997.
• Wet-plate equipment on Early Photography:
  • Horne & Thornthwaite sliding-box camera, 1857
  • Dallmeyer stereo wet-plate camera, 1863
  • Dallmeyer bellows camera for wet and dry plates, 1882
  • G.J. Bourdin Dubroni No. 1, c.1867; wet plates were developed, fixed and washed in this camera!
  • Dark tent for wet plate development.