I appreciate your help. I have a question about your recommendation for cycling 1st and 2nd fixer baths. You say "when your capacity for the first bath is reached, replace it with the second. This can also go through seven changes till you should discard both baths and start over. "
When the previous second bath becomes the new 1st bath, what is the capacity? Surely it doesn't see the same 30 8x10s the original 1st bath got. Can you clarify?
Thanks.
That's exactly what it means. You replace bath one with bath two. It becomes your new first fix and has the same capacity as the original bath one.
You have to understand the idea behind two-bath fixing: The first several prints through fix 1 get adequately fixed there. Fix 2 is hardly used at all for these. As fix 1 approaches capacity (note I don't say exhaustion), there are more complex silver compounds getting carried over to bath two than before, but, these are quickly broken down by the relatively fresh fixer in bath 2. By the time fix 1 reaches capacity, bath 2 is barely getting started, but it has ensured that the prints you've put through it have a really low level of residual silver.
I have never felt that I had to use 2 "tank" fixing except in production situations. It is just too much hassle to me.
And, BTW, for good prints HQ and Metol retention are things to consider. As you re-use fix, these build up in the fix and there is NO test for them. So, be careful.
PE
You can, as PE does, just use a single fixing bath and get as good results. The problem is (and I believe that this is the problem you are interested in), is that the fixer is not used at all efficiently. Haist and others point out that, especially for prints processed for maximum permanence, i.e., residual silver in the fixer at levels of 0.2-0-5 g/l, fixer capacity is quite small. Two-bath fixing allows the fixer to be used more fully.
As for retention of developing agents, etc., I imagine that this is the reason for only using two-bath fixing through seven cycles before discarding. I rarely use my fix for more than a couple of cycles anyway, preferring to err on the side of caution. I would think, however, that with an adequate stop and first fix, that the carry-over of developing agents to fix 2 would be minimal enough to not cause a problem, even after it has become fix one and 70-80 8x10/liter have been run through it, there is still a fresh fix 2 after it and then a thorough wash.
... My point is that checking the first fixer for "exhaustion" doesn't really say very much about the silver level in the final fix tank. My GUESS is that it COULD exceed the number I gave without you knowing it. Given that there recommended numbers have been published, it would be nice to know what you actually have. (Silver estimating papers are the only sensible method I know for a small user, like most people here; even for a pro lab.)
Without any knowledge about this, it's probably best to periodically test the actual film/paper for adequate washing (and perhaps fixing). Note post #11, where PE said, "...but I have found that the retained Silver test and the retained hypo test are the best."
Indeed, even two-bath fixing needs a control. That's why the retained silver test (for fixing) and retained hypo test (for washing) are necessary. Testing regularly while determining your capacities is of prime importance. Pushing your system to failure once or twice will give you an idea of about where maximum capacity is and what kind of safety margin is needed. After one has confidence that the regimen is doing its job adequately, testing occasionally (especially when one suspects the system has been strained, e.g., with a lot of high-key prints, etc.) should be adequate to ensure that prints are being fixed adequately.
I would love a quick, easy and accurate test to determine the dissolved silver content of my second fix. I don't think one exists that is practical, so ST-1 it is!
As for exhaustion of bath 1. I've always used recommended throughput minus a personal safety factor. I see suggested above that a film clip-test may be used to determine the exhaustion of a first fixing bath for prints. I've always been skeptical of using this film-based test for print fixer. I'd appreciate comments about how useful/accurate this method is. If it works well for print fixer too, I will simply start clip-testing my first print fixer the way I do my film fix. I wouldn't base print fixing times on the results, however!
Best,
Doremus