3-37. DRYING AIDS
a. Prevention of Emulsion Swelling. The speed with which x-ray film dries is
dependent upon the quantity of water that must be evaporated from the emulsion. This
speed is proportional to the combined thickness of the emulsions. It is, therefore,
necessary to prevent excessive emulsion swelling. The use of a good fixing bath will
keep swelling to a minimum by shrinking and hardening the emulsion. The emulsion
should be hardened before excessive swelling can occur. Hardening of a swollen
emulsion raises its melting point but does not necessarily reduce its thickness.
Consequently, developing and fixing solutions should be within the optimum
temperature range. These precautions should especially be observed when processing
is done in hot, humid climates where drying always tends to be prolonged. Washing of
the film should be adequate but not excessively long. When processing temperatures
are above 75F, special treatment keeps the emulsion hard, provided that short washing
times are used.
b. Wetting Agent. A wetting agent is a detergent that reduces the surface
tension of water so that the water can drain more rapidly from the radiograph after
washing. This shortens the drying time and eliminates drying marks. There are a
number of wetting agents (labeled under various trade names), which are safe for
photographic purposes. A separate tank of dilute wetting agent is to be used as a final
rinse after washing is prepared by adding 2-1/2 ounces of the detergent to five gallons
of water. After washing, the radiograph is immersed in this solution for 30 seconds and
then drained. The radiograph may then be placed in the dryer. When 400 14 by 17-
inch films, or their equivalent, have passed through the solution, it should be replaced
with a fresh one.
c. Alcohol. The use of alcohol for drying is recommended only where some
emergency requires the use of a dried radiograph in a minimum of time after
processing. Any good grade denatured alcohol may be used for drying films, provided
that when diluted with water it does not turn milky. The alcohol concentration should be
no greater than 70 percent by volume if opalescence of the emulsion or deformation of
the base is to be avoided. After washing, the radiograph is thoroughly drained. Then,
the film is immersed in a tray of alcohol for two minutes at temperatures under 70F.
The tray should be rocked to assure uniform bathing of both film surfaces and to
prevent the film from sticking to the bottom of the tray. This operation causes the water
to diffuse from the pores of the emulsion, and the water is replaced by the alcohol. With
the bulk of the water removed, the film is immersed in a second and final tray of alcohol
to remove any residual water. The film is then drained. The alcohol will evaporate
rapidly to leave a dry emulsion.
d. Dryers. X-ray departments are usually provided with cabinet dryers equipped
with a fan and heating elements. The dryer should always be vented to the outside of
the processing room to prevent excessive humidity. Drawers are provided in which the
films are hung in their hangers. Ordinarily, radiographs should be dried with air
moderately warm. Heat should be used cautiously when drying films in hot, humid
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