Basic Photography Course

certain purposes, one agent may be preferred over
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

developing agents.

PRESERVATIVE

All developing agents in an alkaline state are

affected by oxygen. When the developing agent
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.

The preservative is a chemical with a great

attraction for free oxygen and combines with it when
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

and produces stains before the metallic silver image is
developed completely. By adding enough preservative,
you may remove practically all of the free oxygen from
the solution, the developing agent works as intended,

and no stains are produced. Sodium sulfite is the
preservative most commonly used in developing
solutions.

ACCELERATOR

All developing agents (not developing solutions)

are either neutral or slightly acid. Most 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.

The accelerator serves two functions. First, it speeds

up the swelling of the gelatin in the emulsion. This

swelling permits the solution to penetrate the entire
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
solution.

Because the accelerator is a determining factor in

the activity of a developing solution, it affects the degree

of graininess produced in the negative. This graininess
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
potassium carbonate.

Without an accelerator, there is little or no action.

With some accelerators there is too much action. By the

addition of a bromide restrainer, you may slow down the
action of the developing solution to a controllable
degree.

RESTRAINER

Without a restrainer most developing solutions act

too rapidly and develop unexposed silver halides near
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

agent during development. However, its action is not
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.

TYPES OF BLACK-AND-WHITE

DEVELOPERS

As stated previously, when a photographic emulsion

is exposed to light, there is an invisible change produced
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.

At the beginning of development, there is little

difference in density between the highlight and shadow
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
developing action.

10-2

contents

Basic Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> certain purposes, one agent may be preferred over 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 developing agents. PRESERVATIVE All developing agents in an alkaline state are affected by oxygen. When the developing agent 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. The preservative is a chemical with a great attraction for free oxygen and combines with it when 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 and produces stains before the metallic silver image is developed completely. By adding enough preservative, you may remove practically all of the free oxygen from the solution, the developing agent works as intended, and no stains are produced. Sodium sulfite is the preservative most commonly used in developing solutions. ACCELERATOR All developing agents (not developing solutions) are either neutral or slightly acid. Most 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. The accelerator serves two functions. First, it speeds up the swelling of the gelatin in the emulsion. This swelling permits the solution to penetrate the entire 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 solution. Because the accelerator is a determining factor in the activity of a developing solution, it affects the degree of graininess produced in the negative. This graininess 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 potassium carbonate. Without an accelerator, there is little or no action. With some accelerators there is too much action. By the addition of a bromide restrainer, you may slow down the action of the developing solution to a controllable degree. RESTRAINER Without a restrainer most developing solutions act too rapidly and develop unexposed silver halides near 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 agent during development. However, its action is not 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. TYPES OF BLACK-AND-WHITE DEVELOPERS As stated previously, when a photographic emulsion is exposed to light, there is an invisible change produced 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. At the beginning of development, there is little difference in density between the highlight and shadow 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 developing action. 10-2 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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