another. The temperature of the solution affects the
activity of some agents much more than others.
Hydroquinone, Metol, paraphenylenediamine, and
phenidone are some of the more commonly used
combines with the oxygen in the air, the efficiency of
the developing agent is reduced. When elements
combine with free oxygen from the air or water,
oxidation occurs. Therefore, a preservative is added to
developing solutions to prevent excessive oxidation.
The preservative prolongs the useful life of the
developing solution and prevents stains caused by the
formation of colored oxidation products.
mixed into a solution. A large amount of free oxygen is
in the water used for solutions. When the free oxygen is
left in the water, it oxidizes most of the developing agent
developed completely. By adding enough preservative,
you may remove practically all of the free oxygen from
the solution, the developing agent works as intended,
preservative most commonly used in developing
agents must be in an alkaline state to be effective
reducing agents, thus solutions require an alkali to
activate the developing agent. A developing solution
contains an accelerator so the solution becomes alkaline.
emulsion more quickly. The effect of this action is
physical. The second action is completely chemical. As
the silver halide salts in the latent image are reduced by
the developing agent, the halide elements freed from the
silver are absorbed by the accelerator and combined into
neutral salts. This prevents harmful effects in the
is dependent upon the clumping action of the silver
grains during the development process. The more active
the developer, the higher the pH, and the greater the
clumping action. Therefore, the milder or less alkaline
developers yield finer grain. Common accelerators used
in developing solutions are sodium carbonate and
action of the developing solution to a controllable
the surface of the emulsion. This causes chemical fog,
developing streaks, and an image with low contrast.
During development, some restrainer is released from
the silver and has a restraining action on the reducing
enough to prevent fog. When a restrainer is added,
development time is prolonged and fog is minimized.
Contrast is increased because the activity of the
developing agent is cut down in unexposed areas.
However, too much restrainer greatly retards the amount
of development. The chemical most commonly used as
a restrainer is potassium bromide.
in the minute crystals of silver halides that results in a
latent image. To make the image visible, you must treat
the exposed emulsion in a solution known as a
developer. This solution converts the halides affected by
light to black metallic silver. These black metallic silver
particles form the visible image on the negative.
areas of the film. However, during normal development,
this difference increases because the highlight densities
continue to increase after the shadow areas are
completely developed. Development should stop when
the contrast between the shadows and highlights reaches
a desired difference. The activity of the developer, and
to some extent the type of film, primarily determines this
Basic Photography Course