Developing chemicals are specialized chemicals designed for the development of film and prints. They react with the light sensitive emulsion in film and enlarging paper to bring out the exposed image and fix it permanently while also desensitizing the emulsion to light. Learning how to use developing chemicals is an important step in the learning process of many photographers, except for those who begin in the field of digital photography, which does not have a use for them.
Different types of photography require specialized formulas, with different developing chemicals being used for black and white and color photography. Unique chemicals are also targeted for use on special types of film and paper. The cost of developing chemicals can get high, especially when specialized versions are used. Since the chemicals are also toxic, it is important to dispose of them safely.
The process for developing any type of film or print is more or less the same. It starts with exposure, the moment at which the photograph is taken or the negative is superimposed onto the enlarging paper. A light sensitive emulsion, usually containing silver, reacts to the light as the film or paper is exposed, creating a latent image, which developing brings out and fixes.
Developing must be accomplished in darkness, because the emulsion is still light sensitive. Most photographers use a darkroom for prints, with a low light level provided by nonreactive red lighting. Film must be handled in complete darkness. First, the film or print is dunked into a developer, which slowly brings out the latent image by chemically reacting with the emulsion.
Next, the film or print is dunked into a stop bath, which halts the actions of the developer. After the stop bath, a fixer which will make the image permanent is used. The formulations of all of these unique developing chemicals vary immensely, depending on what is being developed. Finally, the finished print or film strip is washed in water to remove traces of the developing chemicals, and the end product is hung to dry in a dust free environment.
Photographic supply companies carry an assortment of developing chemicals for varying uses. Many developing chemicals come in a powder form which must be mixed with water to form a solution. The use of gloves and eye protection is advised when working with developing chemicals, as prolonged exposure can be harmful.