Radiography in Modern Industry - Kodak

When development is complete, the films are removed from the developer, allowed to drain 1 or 2seconds (not back into the developer tank), and immersed in the stop bath. The developerdraining from the films should be kept out of the stop bath. Instead of draining, a few seconds'rinse in fresh running water may be used prior to inserting the films in the stop bath. This willmaterially prolong the life of the bath.Films should be immersed in the stop bath for 30 to 60 seconds (ideally, at 65 to 70°F or 18 to21°C) with moderate agitation and then transferred to the fixing bath. Five gallons of stop bath willtreat about 100 14 x 17-inch films, or equivalent. If a developer containing sodium carbonate isused, the stop bath temperature must be maintained between (65 and 70°F or 18 to 21°C);otherwise, blisters containing carbon dioxide may be formed in the emulsion by action of the stopbath.RinsingIf a stop bath cannot be used, a rinse in running water for at least 2 minutes should be used. It isimportant that the water be running and that it be free of silver or fixer chemicals. The tank that isused for the final washing after fixation should not be used for this rinse.If the flow of water in the rinse tanks is only moderate, it is desirable to agitate the films carefully,especially when they are first immersed. Otherwise, development will be uneven, and there willbe streaks in areas that received a uniform exposure.FixingThe purpose of fixing is to remove all of the undeveloped silver salt of the emulsion, leaving thedeveloped silver as a permanent image. The fixer has another important function--hardening thegelatin so that the film will withstand subsequent drying with warm air. The interval betweenplacing the film in the fixer solution and the disappearance of the original diffuse yellow milkinessis known as the clearing time. It is during this time that the fixer is dissolving the undevelopedsilver halide. However, additional time is required for the dissolved silver salt to diffuse out of theemulsion and for the gelatin to be hardened adequately. Thus, the total fixing time should beappreciably greater than the clearing time. The fixing time in a relatively fresh fixing bath should,in general, not exceed 15 minutes; otherwise, some loss of low densities may occur. The filmsshould be agitated vigorously when first placed in the fixer and at least every 2 minutes thereafterduring the course of fixation to assure uniform action of the chemicals.During use, the fixer solution accumulates soluble silver salts which gradually inhibit its ability todissolve the unexposed silver halide from the emulsion. In addition, the fixer solution becomesdiluted by rinse water or stop bath carried over by the film. As a result, the rate of fixingdecreases, and the hardening action is impaired. The dilution can be reduced by thoroughdraining of films before immersion in the fixer and, if desired, the fixing ability can be restored byreplenishment of the fixer solution.The usefulness of a fixer solution is ended when it has lost its acidity or when clearing requires anunusually long interval. The use of an exhausted solution should always be avoided becauseabnormal swelling of the emulsion often results from deficient hardening and drying is undulyprolonged; at high temperatures reticulation or sloughing away of the emulsion may take place. Inaddition, neutralization of the acid in the fixer solution frequently causes colored stains to appearon the processed radiographs.WashingX-ray films should be washed in running water so circulated that the entire emulsion areareceives frequent changes. For a proper washing, the bar of the hanger and the top clips shouldalways be covered completely by the running water, as illustrated in Figure 74.Radiography in Modern Industry 111