thiosulfate. It removes this compound from the
emulsion and refills the space it occupied with
nonexhausted fixing solution. Therefore, the function of
the fixing agent is to convert the silver salts remaining
in the emulsion after development to soluble compounds
and to remove these soluble compounds by constantly
diluting and replacing them in the emulsion. The number
of substances capable of functioning as fixing agents is
small because a good fixer must meet the following
film. It also prevents decomposition of the fixer.
Oxidized developer in a fixing bath produces stains.
in the fixer to prevent sulfurization. The preservative
prevents the acid from decomposing hypo into free
sulfur, prevents discoloration of the solution because of
oxidation, and aids in preventing stains.
remain, the developer continues its activity. Even when
the emulsion is thoroughly rinsed in a water bath before
being placed in the fixer, some developer activity
remains. This causes uneven stains in the gelatin of the
emulsion and makes the negative unusable. To stop
development and prevent stains, you must add an acid
neutralizer to the fixer. The most frequently used
neutralizer is acetic acid.
undesirable effects may result when processing is
continued without hardening the emulsion. A hardening
the fixing bath. The most common hardening agent is
potassium alum. The hardening and toughening of the
gelatin by the alum stops the tendency of the emulsion
to swell but leaves it expanded and rigid enough for the
also be high enough to prevent sulfurization. The
reduced acidity of the bath is gradually neutralized by
the alkali of the developer carried into the fixer by the
sludge of aluminum sulfite forms that can make the fixer
to the fixer. This agent is capable of absorbing a large
quantity of the developer before sludge occurs, thus
lengthening the useful life of the fixer.
coarse-grained ones. Thin emulsions require less time
to fix than thick emulsions.
concentration of about 75 percent gives the fastest rate
of fixation. However, because of the tendency of hypo
to bleach out the image, most fixers for negatives have
interpret this to mean that you can raise the temperature
of the fixer above the temperature called for by the
particular process being used.) The temperature of the
fixer is not as critical as the temperature of the developer.
However, you should keep all processing solution
temperatures constant to avoid an increase of graininess.
reduces fixation time.
removed by the fixer, and hence the faster the rate of
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