PHRHTL

03-0161

Photographers' Formulary

Photographer's Formulary 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 film strip) when the test solution is applied.