As a Navy photographer, you must realize that composing and exposing a scene on film does not guarantee top-quality photography. The quality of the finished print depends on the quality of your darkroom work. A perfectly exposed film is useless if it is fogged, scratched, or under- or overdeveloped. Therefore, each step of film processing is important and you must master each step.

During the discussion of basic film processing concepts, both black-and-white and color film processing are covered. The mechanics of black and white and color processing are very similar. The primary differences between processing color film and processing black-and-white film are there are more steps in a color film process, and the time and temperature requirements are more critical.

DEVELOPERS AND DEVELOPMENT

The purpose of development is to convert those parts of the light-sensitive material (film or paper) that has been affected by light to black metallic silver. This produces a visible image from the invisible latent image. Development is usually carried out by bringing the exposed film into contact with a solution that contains a developing agent, but no silver salt. The silver that forms the developed image comes from a reduction of the individual silver halide grains in the film emulsion. This process is called chemical or direct development.

In another process that is seldom used, the developed image is derived from a soluble silver salt contained in the developing solution itself. This process is called physical development. The physical development process can be difficult to use because there is a tendency for silver to be deposited where it is not wanted.

The process of chemical development is most commonly used for film development. Chemical development is the process with which you should be concerned. In chemical development, the individual silver halide grains in the film emulsion are reduced to a black metallic silver. Each grain in the emulsion acts as a unit, in the sense that a grain is either developable as a whole or is not developable. When film development is performed properly, only exposed grains containing a latent image are reduced to black metallic silver. You may ask, Why doesn't the developer develop the unexposed grains as well as the exposed grains? Actually, the unexposed grains are develop able. When development is carried out over a long enough period of time, all grains are developed or reduced to black metallic silver. The density that results from the development of unexposed silver halides is called fog. Thus development is a rate phenomenon and the development of the exposed grains takes place at a faster rate than the unexposed grains.

The individual grains of silver halide in an emulsion are protected against the action of the developer by a chemical layer. When light strikes the emulsion, it breaks down the protective layer at one or more points on each individual light-struck grain. When the exposed film is placed into the developer, the grains are acted upon at these points by the developing agent, and each grain that received more than minimum exposure is quickly reduced to black metallic silver. The amount of blackening (density) over the film surface depends primarily upon the number of grains that have been affected by the developer. Density is also influenced because some grains may not develop to completion in the time the developer is allowed to act on the film.