Developing chemicals are specialized chemicals used in the film and print development process. They react with the light-sensitive emulsion in film and enlarging paper to bring out and fix the exposed image while also desensitizing the emulsion to light. Learning how to use developing chemicals is an important part of many photographers’ learning process, with the exception of those who start out in the field of digital photography, which does not require them.
Different types of photography necessitate specialized formulas, with black and white and color photography requiring different developing chemicals. Chemicals designed specifically for use on specific types of film and paper are also available. Chemical development can be expensive, especially when specialized versions are used. Because the chemicals are also toxic, it is critical to properly dispose of them.
The procedure for developing any type of film or print is nearly identical. It all starts with exposure, which occurs when the photograph or negative is superimposed onto the enlarging paper. As the film or paper is exposed to light, a light sensitive emulsion, usually containing silver, reacts to the light, creating a latent image that developing brings out and fixes.
Because the emulsion is still light sensitive, developing must be done in the dark. For prints, most photographers use a darkroom with nonreactive red lighting to provide a low light level. In order to work with film, it must be done in complete darkness. The film or print is first immersed in a developer, which chemically reacts with the emulsion to slowly reveal the latent image.
The film or print is then immersed in a stop bath, which stops the developer’s actions. After the stop bath, a fixer is applied to the image to make it permanent. Depending on what is being developed, the formulations of all of these unique developing chemicals vary greatly. Finally, the finished print or film strip is washed in water to remove any remaining developing chemicals before being hung to dry in a dust-free environment.
Photographic supply houses stock a variety of developing chemicals for various applications. Many developing chemicals are sold as a powder that must be mixed with water to create a solution. When working with developing chemicals, gloves and eye protection are recommended because prolonged exposure can be harmful.