I went round and round about this very article with some of the experts here (PE and Ralph Lambrecht in particular).
The consensus seemed to be that Haist's results, as quoted by Gudzinowicz, are accurate, but particular to the materials and chemicals he used at the time. Certainly, however, he shows that fixing for optimum permanence is a lot more complicated than most think.
The upshot of the entire discussion was that we all need to do the residual silver tests (and residual hypo tests for washing efficiency) for ourselves in order to find if our particular combination of fixer, film, paper, etc. does the job adequately. I have been using two-bath fixing for film for some years now, after reading Gudzinowicz, and, of course, use two-bath fixing for fiber-base papers. Occasionally, I'll use a single bath for small batches of film, but then I'm tossing the fix well before its exhaustion.
I'd recommend reading up on testing for residual silver (Kodak HT-2 test, etc.) and spend a bit of time testing your own process. That is really the only way you can determine fixer capacity for your materials. I test regularly at the end of a printing run, every month or so, just to make sure, and in-between if there is cause to suspect I've not fixed adequately. It is very reassuring to know that the last print through the fix and with the shortest wash time still passes the test with flying colors.
When printing, I use throughput as a guide and test when there is any doubt at all that capacity has been exceeded (e.g., when a lot of light prints have been through the fixer, or I squeeze one or two more prints out of a fixing bath than my conservative capacity numbers. I use the classic print dilution of a rapid fixer (e.g., Ilford Hypam or Kodak Rapid Fix 1+9) and fix 2 minutes per bath. Since I wash and dry and sort prints for toning before the second fix, I always use a fresh bath 1 and just replace it when the capacity has been reached. I'm skeptical of Ilford's film-strenth, one-minute fixing regime...
For film, I use a clip test to check bath 1, tossing it when the clearing time reaches 2x that in fresh fix. The second bath is then moved to position one if I have enough film to develop, and a new second bath mixed. Often, however, I don't have so many sheets to develop at once, so bath 1 doesn't get replaced with bath 2 about half the time.
Since fixing is so important, and rather bothersome to test for, I find it better to test a "worst-case scenario" every now and then, and see where the limits are for adequate fixing. Once the limits for your process and materials have been determined, it is easy to stay within them. For instance, I know that for me, 35 or 36 8x10 print-equivalents is a conservative and safe throughput for one liter of Rapid Fix diluted 1+9 (that's one liter of the first bath only). However, if I have a day when 38 prints go through the first bath, I will try to compensate with bath 2 (i.e., run fewer print through and extend the times for those last prints a bit). And, I'll test that last print after it comes out of the wash to make sure it was fixed adequately. It's pretty easy to put a drop of HT-2 on a print and wait two minutes.
Best,
Doremus
www.DoremusScudder
