For example, you would run a test page through the washing process, and drop a bit of the hypo on the print. If it liquid turns yellow, the process/print is not clear of Fixer and you qould re-wash the actual prints.
The 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 sylver sulfide-silver thiosulfate on the white of atest print, or the clear area of a negativefilm stripwhen the test solution is applied.
The reliability of the test depends upon the washing procedure.
Shake well prior to each use.