Collodion wet plate

Collodion glass negative. Valladolid around 1865. J. Laurent, photographer.

Scanned glass negative from the "Library of Congress Prints and Photographs Division Washington", title: "Red Cloud and Indians", created 1865–1880

The collodion wet plate is a photographic plate developed by Frederick Scott Archer and Gustave Le Gray in 1850/1851 that produces a photograph as an ambrotype or a negative process . The associated process is known as the wet collodion process or collodion wet plate process and requires prompt processing for the production of the photograph, for example a mobile travel photographer in the early days of photography always had to carry a darkroom tent with him.

The size of the negative was not standardized in the early days; In the middle of the 19th century , formats up to 40 cm × 50 cm were used, for example Francis Frith's photographs from Egypt from the years between 1856 and 1860. However, internationally standardized recording formats emerged later.

Procedure

To make a wet collodion plate, the glass plates are cleaned very carefully and a solution of collodion wool and iodine and bromine salts in ethanol and ether is poured over them . The coating dries to a gelatinous mass and is immediately placed in a solution of silver nitrate in the dark . Here the iodine salts are converted into silver iodide and silver bromide , and these remain finely distributed in the collodion layer.

The plate prepared in this way is taken out of the silver bath and brought into the camera while still damp from the silver solution attached in a light-tight box ( cassette ) , exposed to the light here and then poured with an iron sulfate solution in the darkroom . This immediately precipitates metallic silver as a dark powder from the silver nitrate solution hanging on the plate , and the more intense the light, the more this is attached to the exposed areas of the plate. After this evocation, the image is intensified by pouring on a mixture of iron sulfate and citric acid silver solution to induce a second deposit of silver particles, which are attached to the first deposited so that the image is now sufficiently opaque in the densest areas around the To prevent the passage of light during the copying process.

The negative is now fixed, that is, the still contained silver iodide silver bromide is dissolved out by a solution of sodium thiosulfate , finally washed and coated with alcohol varnish. In the glass negative thus obtained, the light parts of the original appear dark and the dark parts of the original appear light (in transparency). Against a dark background, it appears as a positive image, in that the black background becomes visible in the transparent areas and against this the gray silver powder, which lies on the dense areas of the negative, appears white ( ambrotype ).

This positive effect emerged most beautifully when the picture was slightly underexposed. So one made positives by applying the collodion on dark leather or black wax canvas ( pannotypes ) on black lacquered iron sheet ( ferrotypes ) as a carrier material.

Nikolaus Kuss II (1854–1940) from Mariazell pours iodized collodion onto a pure glass plate.

Further development

A further development of the collodion wet plate is the collodion dry plate (1855, J. M. Taupenot (1824-1856)) and later the gelatin process , which works with the gelatin dry plate and was developed in 1871 by Richard Leach Maddox (1816-1902). This process, which greatly simplifies photography, replaced the collodion process around 1880 and is the black and white process still used today.

Further important improvements were the optical sensitization of the recording material from 1873 by Hermann Wilhelm Vogel and the replacement of the glass plate with celluloid as a layer carrier ( sheet film , from 1869 by the Hyatt brothers).

Today the technique of photography using a collodion wet plate is only used very rarely. Ready-made plates are not available and still have to be made and developed by every photographer immediately before taking the picture. However, there are still a few photographers, for example in Germany, who have specialized in the collodion wet plate process and continue to take photos. A recording session lasts between one and two hours.