WATER RINSE BATH
To slow down the action of development, you must
immerse the film in a water rinse bath. A plain water
rinse bath is commonly used between development and
fixation to slow down the development by removing all
the developer that is clinging to the film (or paper)
surface. A rinse bath does not completely stop
development but retards it. A rinse bath has little affect
on the developer that is actually in the swollen emulsion.
Rinsing is accomplished by quickly immersing the
film in plain, clean water. A water rinse bath should be
changed often to ensure it does not become loaded with
developer. It is better to use running water.
The rinse bath, then, serves two purposes: first, it
slows down development and second, it reduces the
work that has to be done by the acid in the fixer. Rinsing,
therefore, protects or prolongs the useful life of the fixer.
Following rinsing in plain water, the material (that
is still light sensitive) must be treated in an acid fixing
bath to stop the development.
ACID STOP BATH
Although a plain water rinse bath is commonly used
between development and fixation, a better procedure is
to use an acid stop bath. The function of a stop bath is
not only to remove the developer that is clinging to the
surface of the material but to also neutralize the
developer in the swollen emulsion to stop development
completely.
The acid stop bath stops the action of the developer
because developing agents cannot work in an acid
solution. An acid stop bath also helps protect or prolong
the life of the fixer by neutralizing developer carry-over.
An acid stop bath should meet the following
requirements:
lThe pH must be low enough to neutralize the
action of the developer carried over.
The acidity should be limited so the small amount
carried over into the fixing bath does not increase the
free-acid content of the fixing bath and cause
sulfurization.
It must not contain enough acid to produce blister
formations in an emulsion.
You should use only a weak acid stop bath between
development and fixation. Strong acid and the acid in
the fixing bath have a tendency to form carbon dioxide
gas bubbles in the emulsion. When the film is taken from
the developer and placed directly into a strong acid or
fixing bath, these bubbles may break and cause small,
round holes in the emulsion. These bubbles are
sometimes mistaken for pinholes like those caused by
dust particles settling on the emulsion before camera
exposure.
When you are using an acid stop bath, remember
that some of the stop bath is carried into the fixer when
materials pass through it. Therefore, you cannot use a
strong acid (such as sulfuric acid) because it can cause
precipitation of sulphur in the fixer. Acetic acid is the
type of acid used for stop baths. In its pure form as
glacial acetic acid (99.5 percent), it freezes at a
temperature of about 61F. Its freezing tendency gives
it the name "glacial." For use as a stop bath, 99.5 percent
glacial acetic acid is diluted with water to make a 28
percent working solution. Approximately 1/2 ounce of
28 percent acetic (not glacial) acid is added to 32 ounces
of water. The process of determining the concentration
of a liquid is discussed in chapter 8.
FIXING
When a light-sensitive material is removed from the
developing solution, the emulsion contains a large
amount of silver salts (halides) that has not been affected
(developed) by the developing agents. This silver salt is
still sensitive to light, and if it remains in the emulsion,
light ultimately darkens and discolors the salt which
obscures the image. Obviously, when this action occurs,
the negative (or print) is useless.
The fixing bath is used to prevent this discoloration
and to make the developed image permanent. It
accomplishes this by removing the undeveloped silver
halides by making them water soluble. Therefore, to
make an image permanent, you must "fix" the
light-sensitive material by removing all of the
unaffected silver salt from the emulsion.
The fixing bath contains five basic ingredients: the
fixing agent, preservative, neutralizer or acidifier,
hardening agent, and an antisludge agent.
Fixing Agent
All fixing baths must contain a silver halide (salt)
solvent. This solvent is known as a fixer or fixing agent.
The two most commonly used in photography are
sodium and ammonium thiosulfate, commonly termed
hypo (taken from their other chemical name
hyposulfite). Ammonium thiosulfate is used in rapid
fixers that are stronger and require less fixing time.
10-5

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