I guess we are at the point that only testing will help reject the null hypothesis.
I'll try to devise a test, and hopefully, run it, but it'll have to wait till I'm back from my upcoming US trips. Late April or even May... I want to run the tests on what some here called an "exhausted" fixer, or which I think is at the borderline, 2g/l, accumulated through a normal use.
Then, simply note how many prints go through the fix and wash until the stain appears. Now, repeat the experiment adding the wash aid. See if the number of prints that go through the process before the telltale stain appears is significantly more.
To keep from using lots of unexposed paper, one could use 250ml of Ilford Rapid Fixer in an 8x10 tray, which would, if using paper with developed silver images on it, have a capacity (using Ilford's numbers) of 10 8x10 at a "commercial" level of permanence and 2.5 8x10 at the "optimum permanence" level. However, since undeveloped paper is being used, and there is no image silver formed, the capacity should be significantly less due to the increased amount of undeveloped halides, maybe even less than 50% of the throughput recommendation.
I don't know how sensitive ST-1 is, so each print from beginning to end should be numbered and tested, stopping when a few prints show increasing levels of stain from the ST-1 test.
The level of permanence when the stain appears is irrelevant to the experiment; just use the number of prints made before the stain appears as a basis for comparison. If a wash aid really can increase a fixer's capacity by 4x, then one should be prepared to fix four times the sheets used in the first part of the experiment during the second. (I still cannot see how this would be possible...)
If the wash-aid increases capacity by a lesser amount, that should be apparent as well.
Note that fixing has more variables than just the amount of chemistry that's in the bath: agitation, paper type, emulsion type, ambient temperature, freshness of fixer, ... getting reproducible numbers might be quite a challenge unless one creates very reproducible start conditions. This could also mean that in some instances we could fix much beyond the (most likely conservative) numbers given by Ilford.
If you want to do reproducible tests I'd say you prepare AgCl and AgBr (from AgNO3 + KCl/KBr + filtration + drying) and season the fixer with predetermined amounts of AgCl/AgBr. You don't need to prepare much seasoned fixer as you can test fixation and washing with small test clips. This test setup allows to to quickly determine how much Silver can remain in fixer for archival fixing with various fixing and washing techniques.
Once you have these numbers, all you have to do is translate these back to your practical printing setup.
Originally Posted by Simon R Galley
I have just stumbled on one more reference which suggests that using hypo clearing agents extends archival capacity of the fixer from its, otherwise, measly equivalent of 10 8x10" sheets per 1 l. In Tim Rudman's "Toning Book" (2010, ISBN 1-902538-23-4) on page 156, chapter "Archival permanence", section "Hypo-Clearing Agents", 5th paragraph reads:
Hypo-clearing agents play an important part in the archival processing cycle. Firstly, their use extends the archival standard fixer capacity of a single-bath fixer by about a factor of 4.
Hi Rafal, I can't see how this is possible. Is hypo able to dissolve Ag(S2O3)- ?
Tetenal sells test stripsto measure silver content.for me they worked far better than an iodide test solution
Does Rudman provide any scientific proof for his pronouncement?