Developer Aging

T.O. 33B-1-1 6-82 6.7.14.1 Agitation. If films are allowed to develop without any movement, there is a tendency for each area of the film to affect the development of the areas immediately below it. This is because the products of development have a higher specific gravity than the developer. As these products diffuse out of the emulsion layer, they flow downward over the film surface and retard the development of the areas over which they pass. The greater the film density from which the reaction products flow, the greater is the restraining action upon the development of lower portions of the film. Thus, large lateral variations in film density will cause uneven development in the areas below, and this may show up in the form of streaks. 6.7.14.2 Developer Aging. NOTE It is recommended that radiographic inspection facilities use the replenishment method while performing the manual film development process. As films are developed without replenishment, the developing solution becomes exhausted chemically until no developing action can take place. For a given quality of developer, without considering the effects of oxidation, levels of bromide and hardener, and contamination; the development time must be increased for successive films to fully develop them. It is estimated that a five-gallon tank of developer will develop 140 films, size 14 x 17, satisfactorily without excessive increase in development time. It is convenient to divide the total number of films that can be developed by 5 gallons of developer into seven groups of 20 films each. As each group of 20 films, 14 x 17, or equivalent film area is developed, the development time must be increased 1/4 minute, assuming a normal time of 5 minutes at 20°C (68°F). Even when drained, each film carries about 1-1 /2 ounces of developer with it, so developer must be added to keep the tank at the 5-gallon level. When the specified number of films have been developed, discard the solution. This method is known is the exhaustion method of developing. 6.7.14.2.1 Another method of processing is the replenisher method. By adding replenisher solution periodically, the activity of the developer is kept at the same level. In this method films must be removed from the tank quickly without allowing the excess developer to drain off the film back into the tank. Approximately 1 gallon of replenisher should be added for every 40 films, 14x 17, or equivalent film area (based on 5 gallons of developer). If this amount of developer cannot be added at the specified time, too much developer is draining back into the tank. In this case enough developer must be drained from the tank so the replenisher can be added. The developer solution shall be discarded when the replenisher used equals four times the original quantity of developer solution, when it fails the process control requirements or at each two month period, whichever occurs first. For dense radiographs it may be necessary to increase the quality of replenisher added. In this case, it is also desirable to add replenisher at shorter intervals to keep the level of developer activity more nearly constant. 6.7.14.2.1.1 Fresh developer is "wild" and will often result in excessive contrast on the first few films. This is apparently due to the lack of equilibrium between the developer and the reaction products. It is sometimes recommended that a small quantity of old developer be mixed with the fresh developer to temper the solution. 6.7.15 Testing Developer Activity. The success of this method of compensating for the gradual decrease of developer activity will depend upon the use of an adequate system for testing this activity. Since there is no simple direct physical or chemical test of developer activity, the easiest way of making the test is to process, at frequent intervals, film strips exposed in some standard manner, and to compare the densities obtained with a identical strip that had been processed in the fresh solution. The standard strips are cut from a sheet film, 8 by 10 inches or larger, which has been exposed to direct x-rays through a test object. The most suitable form of test object is a stepped wedge made up of a number of sheets of any convenient metal. The wedge should have about 15 steps and be large enough to cover completely the largest cassette or film holder used. When given the proper exposure this should produces series of densities extending over the density range used in practice. It is essential that all strips used in testing a batch of developer receive identical exposures. For this