Developing

There were several different methods for developing negatives:

Inspection

This was the earliest and was still in use well into the 20th century. The negative was placed in a dish with the developing solution, the photographer judged when development was complete by holding the plate to a safelight. To compensate for wrong exposure or lack of contrast it was normal, at the time, for the constituents of the developer to be altered during development based on how the image was appearing.

Factorial

Introduced in 1893 by Alfred Watkins. It was found by Watkins that the time of initial appearance of the image indicated the speed at which the developer was working and that the complete development time was a simple multiple of the appearance time. The multiple differed for each developer and was known as the Watkins Factor. The type of plate and the temperature affected the appearance time but not the Factor. The photographer could alter the Factor depending on the degree of contrast required.

Stand

Very weak developer was used together with a prolonged development time of several hours. With shortened times this method merged into the Time method. A tank was generally used.

Time

Also called Time & Temperature. In the early 1900s development of plates and especially roll-films started to be standardised based on the type of developer, temperature and the type of plate. The popularity of roll-film, which was difficult to process by inspection, and smaller negative sizes were major factors in this change. The change meant that development could take place in light-tight tanks rather than a dish. With development (and enlarging) now able to take place in daylight, away from the darkroom, this branch of photography was opened up to the beginner and part-time photographer.

Thermo

In the early years of Time development the factors affecting development time (temperature, type of developer and plate type) were understood but not well formulated. Around 1908 Watkins, with his skill of systematising, published tables of plate types classified into their development speeds. A table was then used to give the dilution strength of developer to be used based on plate type and developer. This combination gave a solution that required a fixed time (6 ½ m for dish, 24 m for tank) at 60°F to produce a correctly developed plate. For other temperatures the Watkins Time Thermometer or tables supplied with the Watkins Time Developer could be used. The plate classification can be found on the Watkins speed list, plates were grouped into: VVQ, VQ, Q, MQ, MS, S, VS for very very quick, very quick, quick, medium quick, medium slow, slow, very slow. The standard Time Thermometer was calibrated for developers having a Temperature Coefficient of 1.9, for other developers the photographer would need to construct his own scale, a template was provided to do this. Watkins published and patented details on how to construct a calculator with settings for Temperature Coefficient and temperature but this does not seem to have been made commercially. Thermo became obsolete as better information was published by plate manufacturers. The Temperature Coefficient is the rate at which the development time changes with varying temperature, its value is expressed for a 10°C temperature change.

Daylight developing tanks, both plate and roll-film, for the Time method appeared in the early 1900s. They were preceded by what might be described as miniature darkrooms that could be operated in daylight, these took the form of an enclosed tray or developing area, a safelight window to inspect the plate and a spout to pour out the liquid.

Self-Developing Plates

With this type of plate the developing agent was coated on the back of the plate when manufactured. The plate then need only be placed in water, possibly with a little ammonia, to develop. With some proposals two parts of the developer were coated on the plate in different locations which would then mix together when placed in water.

An early proposal was by Leo Baekeland in 1888.¹ Other proposals were from F. Bayer and Co. (1901) and T. Bolas (1906).²

Developers

Developers can be classified into two groups:

• Physical, where the image is built up from metallic silver deposited as a result of the reduction of soluble silver salt in the developer or in the combination of the developer and solutions on the plate.
• Chemical, where the developer reduces individual silver halide grains held within the emulsion.

In earlier years the more commonly used terms were acid (physical) and alkaline (chemical).

Acid (physical)

This type of development was used in the calotype and other similar processes and also in the early years of the wet-plate process.

For use with wet-plates, the developer comprised a developing agent (e.g. pyrogallol) which reduced the silver halide and an acid restrainer (e.g. acetic acid). It is the acid restrainer that gives the name to this type of developer, without a restrainer silver would be deposited rapidly and uniformly over the whole plate producing fog.¹

Alkaline (chemical)

Pyro-ammonia developer was proposed in 1862 by Major C. Russell for use with bromo-iodised collodion dry plates (tannin process) and fully described the following year. At around the same time Thomas M. Leahy of Dublin used ammonia and also soda 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 to increase sensitivity. Alkaline developer was used more or less exclusively with gelatine dry plates.²

Wardley had used a developer of pyrogallol without citric or acetic acid or silver nitrate. The plates were then intensified with the normal developer comprising pyrogallol, acetic acid and silver nitrate.³

The developer solution comprised:

• Developing Agent - which reduced the silver halide grains to metallic silver.
• Alkali - which acted as an accelerator to the developing agent. Common substances were ammonia, sodium carbonate (soda ash), sodium hydrate (caustic soda, sodium hydroxide), potassium carbonate, potassium hydrate (caustic potash).
• Preservative - to prevent oxidation and discolouration of the developer. Sodium sulphite was commonly used.
• Restrainer - to protect the unexposed grains from the developing agent. Potassium bromide was commonly used.

Developing Agents and Solutions

Gallic acid

Used in the calotype and other processes. Silver nitrate and acetic acid usually formed part of the developing process.

Ferrous sulphate (proto-sulphate of iron)

Introduced by Robert Hunt in 1844 for use with paper processes. It was later the commonly used developer for wet-plates (especially positive collodion images) where it was used with acetic or nitric acid.⁴

Pyrogallic acid (pyrogallol, pyro)

First published details were by Frederick Scott Archer in 1850. Used with paper negatives and with wet-plates. It was the commonly used developer for dry collodion plates.⁵

Pyro-ammonia

First of the alkaline developers, introduced by Russell in 1862, later widely used with gelatine emulsions. Used less after 1900.

Pyro-soda

Introduced by Herbert B. Berkeley around 1882.

Hydroquinone (quinol)

Introduced by Abney in 1880.⁶

Pyrocatechin (catechol)

Introduced by Eder and Tóth in 1880.⁷

Ferrous Oxalate

Suggested by Carey Lea in 1877 and introduced by Eder in 1880.⁸

Hydroxylamine

Introduced in 1884 by Egli and Arnold Spiller.⁹

Phenylhydrazine

Introduced in 1885 by Jacobsen.¹⁰

Paraphenylenediamine

Introduced by Andresen of Agfa in 1888.¹¹

Eikonogen

Introduced by Andresen of Agfa in 1889.¹²

Paraminophenol

Introduced by Andresen of Agfa in 1891. Sold under the names of Rodinal by Agfa and as Azol.¹³

Paraminocresol

¹⁴

Metol

Introduced by Bogisch in 1891, sold by Hauff.¹⁵

Glycin

Introduced by Bogisch in 1891, sold by Hauff.¹⁶

Amidol

Introduced by Bogisch in 1891, sold by Hauff.¹⁷

Ortol

Introduced by Hauff in 1897.¹⁸

Hydramine, (hydroquinone and paraphenylenediamine)

Introduced by Lumière and Seyewitz in 1899.¹⁹

Adurol

Introduced by Lüppo-Cramer in 1899. Produced by Schering and Hauff.²⁰

Diogen

Introduced by Agfa around 1898.²¹

Kachin

Introduced in 1899.²²

Metol Hydroquinone (metol-quinol, M.Q.)

Introduced by Lumière and Seyewitz in 1903.²³

Chloranol

Introduced by Lumière and Seyewitz in 1913.²⁴

Phenidone

Introduced by Ilford in 1940, usually mixed with Metol.²⁵