Table 6-17. Manual Washing of Radiographic Film

T.O. 33B-1-1 6-78 Table 6-17. Manual Washing of Radiographic Film. MANUAL Approximate Film-Washing Times at 68⁰ F Class of Film Rate of Water Change Washing Time I 4 times per hr. 35 minutes I 8 times per hr. 20 minutes II 4 times per hr. 35 minutes II 8 times per hr. 20 minutes III 8 times per hr. 35 minutes IV 4 times per hr. 35 minutes IV 8 times per hr. 20 minutes 6.7.10.1 If the temperature of the wash water falls below 50 degrees F, it is not possible to adequately remove the fixer from the emulsion in the above length of time. Washing takes three times as long when the temperature is between 50 to 60 degrees F as it does at 70 to 75 degrees F. Thus the rule for washing time for X-ray films is true only when the wash water is relatively warm. If the film has been over fixed and then washed at 50 degrees F, there is no practical way to remove enough fixer to prevent fading of the image. In addition, if the temperature difference between fixer and wash water exceeds 15 degrees F, there is a possibility of unequal swelling of the emulsion known as reticulation. 6.7.10.2 Wetting Agent. The use of a wetting agent between the washing and drying operations is highly recommended. When the films are removed from the wash tank, small drops of water will cling to the emulsion. Areas under these drops will dry more slowly and cause distortion of the gelatin, changing the density of the silver. These are frequently visible and can be troublesome in film interpretation. Most water also contains large amounts of solid material in the form of calcium and other chemicals which will remain on the film as a white residue the water drops have, evaporated. Such "water spots" can be prevented by immersing the washed films in a wetting agent for one to two minutes before transfer into the drying cabinet. Various detergents or commercial wetting agents can be used. 6.7.11 Drying. The final step in processing is the drying of the X-ray film. It consists simply of allowing the water on the film to evaporate slowly. This is easily accomplished by hanging up the films in a dry rack where the film hangers can be suspended. Where a large number of films must be handled special equipment may be necessary. Drying by any method will be accelerated if the film is immersed in a solution of water and wetting agent following washing. In addition to speeding drying time, this technique also prevents the formation of watermarks or streaking on the emulsion. 6.7.12 Dark Room Equipment. The size of the processing room depends upon the volume of work to be processed. If a darkroom is available which is used for other film processing, there is no reason why it cannot be used for processing radiographs unless the various activities interfere with each other. If new facilities are desirable, the floor space should be kept to a minimum considering the equipment that must be used in the dark room. For safelight and process control in the dark room see the process control section in chapter 1.