Formulary's Residual Hypo Test is a simple chemical test that can be used to determine if a print or film strip has been adequately washed. The test is based upon the formation of a yellow stain of silver sulfide-silver thiosulfate on the white of a test print, or the clear area of a negative filmstrip when the test solution is applied. The test will give accurate results if the print or film has been treated with Hypo Clearing agent and washed in water or just washed in water. The test will not give accurate results if Hypo Eliminator has been used in the washing procedure. Hypo Eliminator contains ammonia which complexes with the silver ions in the Residual Hypo Test Solution decreasing their effective concentration.