Collodion process

The collodion wet plate is a 1850/1851 developed by Frederick Scott Archer and Gustave Le Gray photographic plate that creates as Ambrotype or through a negative process, a photographic image.

The corresponding method is called wet collodion process and requires timely for making the photograph processing, so had about a mobile travel photographer in the early days of photography always lead a darkroom tent with it.

The size of the negative was not yet standardized during the initial period; Mid-19th century formats were used to 40 × 50 cm, such as Frith's photographs from Egypt from the years 1856-1860. Later, however, internationally standardized recording formats were out.

Method

To produce a collodion wet plate you clean the glass plates very carefully and pour over them with a solution of cellulose nitrate and iodine and bromine salts in ethanol and ether. The coating dries to a gelatinous mass and is immediately placed in the dark in a solution of silver nitrate. Here, the iodine salts transform into silver iodide and silver bromide, and these remain dispersed in collodion.

The prepared plate is taken out of the silver bath and brought still damp from an attached silver solution in a light- tight fitting box ( cassette ) into the camera, here exposed to the action of light and then doused in the dark with a solution of ferrous sulfate. This suggests from the hang to plate silver nitrate solution immediately metallic silver as a dark powder down, and this depends on the exposed areas of the plate, the stronger the more intense the light worked. The picture is further enhanced by this evocation by still caused by pouring a mixture of ferrous sulfate and lemon acid silver solution a second precipitation of silver particles that are deposited on the erstniedergeschlagenen, so that the image is sufficiently opaque now in the densest points to help to prevent the passage of light during the copying process.

The negative is then fixed, that is, the silver iodide or silver bromide contained is dissolved by a solution of sodium thiosulfate, and finally washed with alcohol and covered varnish. In the glass negative thus obtained, the bright parts of the original image appear dark and the dark parts of the original light ( in phantom ). Against a dark background, it appears as a positive image by the black background is visible in the transparent places, and against this the gray silver powder, which is located on the dense bodies of the negative, as will appear white ( Ambrotype ).

This positive effect came out best when the recording was a bit underexposed. So you made ​​positive by the collodion was applied to dark leather or black oilcloth ( Pannotypen ) on black painted sheet iron ( ferro- types) as a support material.

History and Development

A further development of the collodion wet plate is the collodion dry plate (1855, JMTaupenot, (1824 - 1856) ) and later the gelatin method that works with the gelatin dry plate and 1871 by Richard Leach Maddox (1816 - 1902) was developed. This photograph very simplistic method solved the collodion from around 1880 and is still in use until the black and white process.

Other important improvements were the optical sensitization of the recording material in 1873 by Hermann Wilhelm Vogel and replacing the glass plate by celluloid as the substrate ( sheet film, in 1869 by the brothers Hyatt).

Today, the technology of photography using collodion wet plate is only very rarely used. Ready -prepared plates are not available and must still be made even by each photographer just before recording and developed immediately.