CHAPTER 9
CHEMICAL MIXING
When light-sensitive emulsions are used, photog-
raphy is essentially a chemical process. You depend
upon the chemical process to produce visible and
permanent images. An important requirement for
optimum photographic processing is the careful and
correct preparation of photographic solutions. Improper
mixing of chemicals or contamination during mixing
can have far-reaching effects on operations, quality,
production, and mission accomplishment in the imaging
facilities of the Navy. It is often difficult to determine
the cause of poor quality when improper chemical
mixing is at fault, and the need for discarding incorrectly
prepared or contaminated solutions cuts down on
production and wastes money.
The main function of the darkroom portion of the
photographic process is to develop film and produce
prints, and this requires photographic chemistry. It may
be your job to ensure that all chemicals needed are
mixed and checked for quality. "This is a responsibility
that you cannot take lightly." A solution that is mixed
improperly may cause an entire mission to be lost. You
must use the utmost precautions when mixing, checking,
or analyzing the photographic solutions used in your lab.
PHOTOGRAPHIC CHEMICAL AND
SOLUTION STORAGE
When you receive chemicals in your imaging
facility, the cartons, packages, or containers should be
dated to show either the date received or the date
shipped. This helps provide proper stock rotation and
systematic control of chemical usage. Chemicals should
be issued from the storeroom on a first-in-first-out
(FIFO) basis.
Unmixed chemicals should be stored in their
original, unopened containers in a cool, dry,
well-ventilated storage area where the temperature is
maintained at or about 75F with a relative humidity of
about 40 percent.
Prepared solutions, like dry chemicals, also must be
protected from adverse conditions, especially oxidation
a n d c o n t a m i n a t i o n . W h e n t h e f o l l o w i n g
recommendations are adhered to, most "unused"
solutions stay in good condition for a reasonable period
of time:
Small amounts of replenisher and stock solutions
are best kept in stoppered or screw-cap bottles. Glass
bottles are best for developer and developer replenisher.
Screw caps must be free of corrosion, foreign particles,
cardboard inserts, and be airtight. Never interchange
bottle tops from one bottle to another. A cap-to-bottle
color or number code is suggested.
When large bottles are used to store solutions, the
air space in the bottle is increased each time the solution
is removed. Since this increases the chance for
oxidation, store solutions in small bottles instead. The
entire contents of a small bottle can then be used at one
time. However, a small air space should be left even in
small bottles. This allows for varying solution volume
due to temperature changes and keeps the cap from
loosening or the bottle from bursting.
When tanks are used for the storage of large
volumes of solutions, they should have floating lids to
protect the solutions from aerial oxidation Dust covers
also should be used to cover the top of the tank. The tank,
the lid, and the cap should be coded in such a way that
they are reassembled with the correct parts.
Always follow the storage and capacity
recommendations of the manufacturer. They are
packaged with the chemicals. Do not use chemicals that
have been in storage too long.
Before you use any solution, no matter how long
it has been mixed or in storage, check it for
discoloration. Each solution has its own "signature" or
characteristic appearance; and any change from normal
may be a sign that it will produce unsatisfactory results.
Check both sides and the bottom of the tank for
precipitates. If there are any, carefully stir the solution
to redissolve them. When you are unsure of the quality
of the solution, discard it.
Most photo-processing chemical formulations are
based on both their photographic qualities and their
chemical stability or keeping qualities, both on the shelf
before mixing and as prepared solutions. After
long-term storage, chemicals may lose some of their
chemical activity.
9-1

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