I imagine the test should be fairly straghtforward. Simply fix a prints in a single fixing bath, do not use a wash aid, wash them thoroughly (overkill here to be sure) and subsequently test them sequentially for residual silver with ST-1. (I know ST-1 test doesn't really give quantifiable results, but it should work for comparison purposes). To really be accurate, you should fix unexposed paper of the same type and size. Unusably expired paper would be ideal for this if one had, or could get it. You should also fix for the same time
Originally Posted by Rafal Lukawiecki
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.
Last edited by Doremus Scudder; 03-24-2013 at 05:48 AM. Click to view previous post history.