The Foma Fomacitro Stop Bath 250 ml is a liquid concentrate, citric-acid based, odorless stop bath with indicator. It is designed for processing all black and white photographic films and papers. Dilution with water for a working strength solution is 1:19. Stopping time is 10 - 20 sec for film and RC papers, and 30 sec for fiber-base papers. Stop baths are helpful when abrupt and exact interruption of development is required, such as in extremely rapid development, since they prevent the fixer from becoming contaminated by developer rests. This prolongs the life of the fixer. A color change of the working solution from yellow-orange to blue-green lets you know that the bath is exhausted and should be exchanged for a fresh one.