tank has hardened the equivalent of 180 14 by 17-inch films and then when used as the
number one tank can be used for another 180 of the same size films or their equivalent
for clearing purposes. Once the routine has been established, this system of rotation
between tanks will assure the production of well-fixed films indefinitely.
3-31. WASHING PROCESS
Proper washing ensures the permanence of radiographs as records. Washing of
radiographs must be regarded as a chemical operation, the object being to remove
residual chemicals and silver salts from the film. If these are not removed, the image
will discolor or fade, eventually stain (brown stain of silver sulfide), and the entire film
may deteriorate. This is especially true when the radiographs are stored under
conditions of high temperature and humidity. As the fixing solution nears the exhaustion
point, the concentration of silver salts becomes so high that the washing process should
be more thorough at this time.
3-32. WATER FOR WASHING
a. Supply. Any drinkable water should be satisfactory for film washing.
Normally x-ray films are washed in running water circulated so that the entire emulsion
area and every portion of the wash tank receive frequent changes. In tank processing,
the bar of the hanger and the top clips should always be covered by the water. When
fresh water is in short supply, radiographs may be safely washed in seawater. There is
also a special procedure (to be discussed in this sub course), which can be used when
water is scarce and which will ensure the processed radiograph's permanence.
b. Filtration. The bulk of microscopic and animal matter sometimes contained
in tap water or water from other sources should be removed by filtration. Several
thicknesses of gauze placed over the outlet of the water supply will provide some
degree of filtration if some other is available. The gauze filter should be cleaned or
3-33. WASHING TIME
a. General. The time required for adequate washing depends principally upon
the type of film, the rate of water flow through the tank, and the temperature of the
water. If circumstances demand, a shorter washing time may be used. As long as the
film is not subjected to high heat and humidity conditions, it may be thoroughly washed
at a later time (within three to six months). Generally, if a radiograph is to remain in a
temperate zone, less washing is necessary than for those kept in a tropical or
subtropical region. However, every effort should be made to wash the film properly
during its initial processing, since it is unlikely that at this time the area of ultimate
storage can be determined.
b. Washing in a Single Tank. If the hourly flow of water through a single tank
is four times the capacity of the tank, 30 to 40 minutes is required for washing x-ray film