at a water temperature of about 70F. When the flow is eight times the tank's capacity
per hour, the washing time is 25 to 30 minutes. Shorter washing times than these
should not be used no matter how frequently the water in the tank is changed. If the
flow of water through the tank is very slow, the films should remain in the water even
longer than the above specified times. The washing time should be measured from the
immersion of the last film in the wash water, since washed and partly washed films
fixing bath chemicals rinsed into water from newly added films.
c. Washing in a Two-Compartment Tank. The total volume of water may be
divided into several small units, especially when flow is inadequate. In the two-stage
cascade system of washing, the flow of water is from right to left while the flow of films
in normal processing is from left to right. The film laden with fixing bath is placed in the
first compartment of the tank and is bathed with a very dilute solution of water and fixing
bath salts. After remaining in the first compartment approximately five minutes, the
radiograph is placed in the second compartment. Here it is bathed with uncontaminated
fresh water for an additional five minutes--giving a total of 10 minutes washing time. At
no time should a film fresh from the fixing solution be placed in the second
compartment.
3-34. TEMPERATURE OF WASH WATER
The temperature of the wash water is important. It should range between 68
and 70F, if possible. This range is about 40 percent more efficient than 40 would be,
for instance, and temperatures above 75F tend to soften the emulsion, leaving it open
to damage. In general, the temperature of the wash water should approximate that of
the other processing solutions.
3-35. USING SEAWATER FOR WASHING
Film may be washed in seawater, but they should receive an additional final
washing in fresh water for at least five minutes. Otherwise, the film may attract excess
moisture and the image may fade rapidly. Seawater does remove the chemicals more
rapidly than fresh water and washing time may be cut in half. Washing in seawater or
other salt water may be done at lower temperatures, even at 50F or lower. When
processing solutions have been mixed with seawater, it is advisable to wipe the
surfaces of the radiograph with a soft, wet cloth after washing.
3-36. THE DRYING PROCESS
The success of any drying operation lies in the rapid removal of the water from
the emulsion. The most common procedure is the use of a rapid flow of air (with or
without the aid of heat) over the edges of the film surfaces. Drying often takes more
than all the other operations together, so it is often a bottleneck in the flow of
radiographs through the processing room. The radiographs are wet and vulnerable to
damage, so they should not be removed from their hangers. If they are not handled
carefully, dust may become embedded in the emulsion or the film may get scratched
and abraded.
MD0954
3-17
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