LESSON 3
would be totally exhausted and of no more use. Exhaustion can be defined as
being a point below which results are of unacceptable quality.
d. As a developer solution becomes exhausted, we must analyze what
happens to each component of the developer.
In a previous lesson, you
learned the parts of a developer and their function. You recall:
(1) Solvent or water is used to dissolve the chemicals.
(2) Reducing agents are used to change the exposed silver halides to
black metallic silver.
(3) Preservatives are used to prolong the life of the reducing agent.
(4) Accelerators speed up the action of the reducing agent.
(5) Restrainers slow the action of the reducing agent.
(6) Special additive ingredients are used when processing at higher
than normal temperatures, to minimize aerial fog, and to act as a wetting
agent.
(a) When a developer has been in continuous use for a period of
time and has reached the point of exhaustion, the most noticeable change is
that it has lost efficiency. First, the quantity of the solution is less,
due partly to evaporation, but chiefly to carryout. Second, the accelerator
or alkali, developing agent (reducing agent), and preservative are reduced
in strength and volume. Also the exhausted solution contains an increased
amount of bromide, waste products such as gelatin, sensitizing dyes,
antihalation dyes, free silver, etc. Still another thing to consider is the
presence of foreign matter, dust, dirt, etc., which could be removed by
filtration.
(b) The increased formation of bromide in an exhausted developer
solution is of great concern.
The emulsion coating on sensitized film
material contains bromide which is released into the developer during
processing.
This
action
eventually results
in
excessive bromide
concentration, called bromide buildup, which increases restraining action.
Since the excess bromide slows down the action of the developer at an ever
increasing rate, the first consideration in designing a developer
replenisher is to control the bromide buildup.
Your attention must be
turned to replacing these consumed components, i.e., the accelerator,
developing agents, and the preservative.
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