Dry Collodion Plates

The wet collodion process could be operated well in a studio but for outdoor work the requirement to sensitise, expose and develop the plate whilst still moist necessitated chemicals, water and a portable darkroom, in the form of a tent, be added to the travelling photographer's equipment. This led to the search for a dry collodion plate that remained sensitive for at least a few days prior to exposure and did not need to be developed immediately.

If an ordinary wet-plate was allowed to dry the excess silver nitrate from the dipping bath would crystallise on the surface of the plate and decompose the silver iodide, producing clear spots on the negative; if the plate was washed to remove the free silver nitrate it lost its sensitivity.

There were many different dry plate processes, as most required that the plate be made by the photographer success depended on the process producing consistent and repeatable results; in this respect the amount of washing given to the plate to remove the free silver nitrate was particularly important. At first all of the dry collodion processes were slower than wet-plates but later the speed was improved. All were replaced by the gelatine dry-plate.

One of the earliest suggestions for extending the working time of wet-plates was by M.A. Girod in 1853, this was to enclose the collodion film by placing a sheet of glass over the face of the sensitised wet-plate, the plates were separated prior to development.¹

Collodion with Preservatives

There was no agreed theory on how to achieve a dry plate but most processes attempted to maintain the pores in the collodion (by filling with another substance) so that subsequently the developer would be able to penetrate and, secondly, to give a varnish to the plate that locked-in the moisture. Collodion, when dried and again wetted, tended to separate from the glass so a substratum of gelatine, india-rubber or albumen was often used to fix the collodion to the glass. With most processes the free silver nitrate, present after the plate was dipped, was largely removed by washing before the plate was dried, it would then be returned as part of the developing procedure.

Resin/Varnish

The Abbé Desprats proposed adding resin to the collodion, the plate was washed on its removal from the dipping bath. Prior to development the plate was dipped in a silver nitrate bath. The plates remained sensitive for many days and required around three times the exposure of a wet-plate. Dubosq proposed a similar process but used amber varnish rather than resin.²

Dextrine

Proposed by Dupuis. The plate was washed after removal from the silver nitrate bath and coated with dextrine.³

Magnesium nitrate

Proposed by Spiller and Crookes in 1854. After sensitising, a deliquescent substance such as magnesium nitrate or zinc nitrate was spread over the plate which was not washed.⁴

Honey

Proposed independently by Maxwell Lyte and George Shadbolt in 1854. In the Maxwell Lyte process the sensitised plate was coated with a honey and glycerine mixture, the plates retained their sensitivity for a few hours, exposure times were around three times that of a wet-plate. The Shadbolt process used honey and alcohol, the plates retained their sensitivity for longer but were less sensitive. Hardwich notes that results from the honey process varied depending on the amount of washing given to the plate prior to applying the honey. If much free silver nitrate remained, the sensitivity was increased but the plate did not keep for very long (a component of honey reduces the silver nitrate to the metallic state).⁵

Collodio-albumen

Developed by Taupenot in 1855. After sensitising a collodion plate with silver nitrate it was washed and coated twice with iodised albumen and dried. It was dipped again in sliver nitrate a few hours before use (this second dipping acted on the albumen layer). This was a popular process that produced fine, detailed images but was very slow. The sensitive plates could be kept for a few weeks before exposure. Development could take up to twelve hours.⁶

Oxymel

Introduced by J.D. Llewelyn in 1856. A wet collodion plate was prepared in the normal way, after removal from the sliver nitrate bath it was washed, placed in a bath of honey and acetic acid and then dried. The prepared plates could be kept for several days before being used and required around six times the exposure of a wet-plate. The developer used was pyrogallic acid with citric acid. This was a modification of the honey process with the important difference that the free silver nitrate was fully removed prior to coating with preservative, as a result the plate was slower but could be kept for longer, the results were also more consistent.⁷

Collodion silver bromide

Developed by Richard Hill Norris in 1856. A conventional wet-plate was fully washed and coated with gum arabic, gelatine or similar, they could then be kept for several months before use. When introduced the speed was about half that of a wet-plate, later this was increased to be roughly equal. The plates were sold by the Birmingham Dry Collodion Plate and Film Co. and were the first dry collodion plates to be commercially produced, they proved popular and were widely sold. In his patent Hill Norris suggested that the film could be stripped from the glass plate and mounted on a gelatine sheet.⁸

Fothergill's process

Introduced in 1858 and similar to the collodio-albumen process. A wet collodion plate was prepared in the normal way, after removal from the dipping bath it was placed in a bath of water and then coated with an albumen solution containing ammonium chloride and again washed. The prepared plates would keep for a considerable time. Exposure times were around five times that of a wet-plate.⁹

Tannin

Proposed by Major C. Russell in 1861. The collodion plate was washed and coated with a tannin solution. The developer was a pyrogallic acid, silver nitrate solution containing acetic acid. Russell's improvements to this process resulted (1862) in the introduction of an alkaline pyro-ammonia developer (for which bromo-iodised collodion was needed). The plates were as quick as wet-plates. At around the same time Thomas M. Leahy of Dublin used ammonia to bring out a weak image on a tannin plate which could then be intensified. In America ammonia fumes had already been used prior to development.¹⁰

Gum and Gallic acid

Introduced by Russell Manners Gordon in 1868 and improved the following year by using an iron developer.¹¹

Albumen-beer

Proposed by Abney in 1874. This was a complicated process involving two coatings of preservative.¹²

Others

From the mid 1850s to the late 1870s most magazines and periodicals would have contained an article on a dry plate process; sometimes new, sometimes having a different preservative and often simply a different way of working an existing process. Of note were: R.F. Barnes (of Barnes & Judge, photographers of 64A New Bond St.) an albumen coating and several preservatives; Robiquet, yellow amber; Charles Clifford, beer with unwashed plates; Herman Krone; Keene, gum arabic and tannin as preservative with a bromo-iodised collodion; Bartholomew, gelatine coating followed by a solution of carbonate of soda; Bartholomew, morphine in either the collodion or the dipping bath. Baratti, coffee process.¹³

Collodion Emulsion

Collodion silver iodide and silver chloride emulsions were suggested by Gaudin in 1853 and 1861. In 1860 Harry Bellini announced a coating for plates consisting of shellac, gum sandarac in alcohol and ether with silver iodide, silver bromide, lactate of silver and iron iodide, there being no separate dipping bath. However in a subsequent note in the Phot. News it seems that the process was less than successful. In 1861 Henry Dixon described mixing the silver nitrate with the collodion prior to coating the plate.¹⁴

In 1864 Sayce and Bolton described a collodion silver bromide emulsion. Crystallised silver nitrate to which a little water was added to produce a 'pulp' was mixed with bromised collodion. The emulsion could then be used wet or coated with tannin as a preservative and dried. Development involved solutions of pyrogallic acid, carbonate of soda and bromide of potassium, all prepared separately. Silver nitrate could be used as an intensifier. The plates were sold by the Liverpool Dry Plate and Photographic Printing Co.¹⁵

In 1874 W.B. Bolton described an improved process where the emulsion was washed, previously the coated plate was washed to remove the excess silver nitrate. An ordinary bromide emulsion was coated on a plate, when dry it was cut into small squares and placed in a jar where it was washed and then dried. Before use it was dissolved in alcohol and ether. A preservative (tannin or soap) was added to the emulsion. In 1875 Beechey described an emulsion containing pyrogallic acid as a preservative.¹⁶

The Liverpool Dry Plate and Photographic Printing Co. advertised (1869) a dozen whole-plates at 14/-.¹⁷

References & Notes