Radiography in Modern Industry - Kodak

The quantity of replenisher required to maintain the properties of the developer will depend on theaverage density of the radiographs processed. It is obvious that if 90 percent of the silver in theemulsion is developed, giving a dense image over the entire film, more developing agent will beconsumed. Therefore, the developer will be exhausted to a greater degree than if the film weredeveloped to a low density. The quantity of replenisher required, therefore, depends on the typeof subject radiographed. In the processing of industrial radiographs that have a relatively largeproportion of dense background, some of the original developer must be discarded each timereplenisher is added. The exact quantity of replenisher can be determined only by trial and byfrequent testing of the developer.The replenisher should be added at frequent intervals and in sufficient quantity to maintain theactivity reasonably constant for the types of radiographs processed. It is obvious that ifreplenisher is added only occasionally, there will be a large increase in density of the film afterreplenishing. By replenishing frequently, these density increases after replenishing are kept at aminimum. The quantity of the replenisher added each time preferably should not exceed 2 or 3percent of the total volume of the developer in the tank.It is not practical to continue replenishment indefinitely, and the solution should be discardedwhen the replenisher used equals two to three times the original quantity of the developer. In anycase, the solution should be discarded after three months because of aerial oxidation and thebuildup of gelatin, sludge, and solid impurities.Arresting DevelopmentAfter development is complete, developer remaining in the emulsion must be deactivated by anacid stop bath or, if this is not feasible, by prolonged rinsing in clean running water.If this step is omitted, development continues for the first minute or so of fixation and, unless thefilm is agitated almost continuously during this period, uneven development will occur, resulting instreakiness.In addition, if films are transferred to the fixer solution without the use of an acid stop bath orthorough rinsing, the alkali from the developer solution retained by the gelatin neutralizes some ofthe acid in the fixer solution. After a certain quantity of acid has been neutralized, the chemicalbalance of the fixer solution is upset and its usefulness is greatly impaired--the hardening actionis destroyed and stains are likely to be produced in the radiographs. Removal of as much of thedeveloper solution as possible before fixation prolongs the life of the fixer solution and assuresthe routine production of radiographs of better quality.Stop BathA stop bath consisting of 16 fluidounces of 28 percent acetic acid per gallon of bath (125 mL perlitre) may be used. If the stop bath is made from glacial acetic acid, the proportions should be 4½fluidounces of glacial acetic acid per gallon of bath, or 35 mL per litre.WarningGlacial acetic acid should be handled only under adequate ventilation, and great care should betaken to avoid injury to the skin or damage to clothing. Always add the glacial acetic acid to thewater slowly, stirring constantly, and never water to acid; otherwise, the solution may boil andspatter acid on hands and face, causing severe burns.Radiography in Modern Industry 110