Doremus Scudder
Member
The two formulas I gave if ! the selenium toner test and the HT2 test, I have used both for 60 years, both give the same results, I did not give any formula for ST1, are, over here, used for as a residual fixer test, at least where I grew up, and bot are given as residual fixer tests in many formula books as tests for residual fixer tests for both film and paper, as these days I print mainly on RC I don't need these tests, and even with FB paper I don't bother, but neither test has let me down in my experience,
None of that changes the fact that selenium toner reacts with silver in the emulsion, not hypo. That's why it tones prints in the first place and why it can be used as a residual silver test, which is a test for adequate fixation. It doesn't matter whether it's over here, over there or wherever.
I mentioned the ST-1 test only to point out that using selenium toner as a test is a substitute for it. That is how it first came to my attention years ago and what I use it for these days.
FWIW, my source is the Kodak Tech Pub. J-1, "Kodak Processing Chemicals & Formulas," 1973, p.41. Here's the relevant section, right after the section on the ST-1 test:
"Testing with KODAK Rapid Selenium Toner
If you wish to use a more stable reagent than KODAK Residual Silver Test Solution ST1, you can use a dilute solution of KODAK Rapid Selenium Toner to test whether prints are thoroughly fixed.
To use, dilute 1 part of KODAK Rapid Selenium Toner with 9 parts of water. These proportions are not critical. Using this solution, follow the directions given above for the use of KODAK Residual Silver Test Solution ST-1. [Instructions for using the ST-1 test are: "Place a drop of the test solution on the margin of a squeegeed film or print... Remove the solution with a clean white blotter after 2 or 3 minutes. Any yellowing of the test spot other than a barely visible cream tint, indicates the presence of silver. If the test is positive, residual silver can be removed by refixing the print or negative..."]
NOTE: The test fails where a very large excess of hypo is present, as in stabilized prints."
I have never seen any reference in the literature to using selenium toner as a test for residual hypo. Certainly, Kodak does not mention it. If you have any such references, then I'd be very interested in seeing them.
Best,
Doremus