Hey all! Thanks for all the recommendations, I will follow
@xkaes amazing instructions. That is what I need in terms of figuring out my workflow and getting to know my materials. Also the double the clearing times for the film as many of you suggested!
I think is always best to really understand the processes and that usually means taking things a bit beyond the manufacturers instructions. Specially useful because I make my dev and fix chemicals for film.
@pentaxuser I've been fixing film for 6 min when fresh and 8 minutes after 10 rolls aprox. For the paper around 2 minutes with Ilford's Rapid Fixer.
Thanks again to everyone for your help!
Well, since you want to understand the processes better:
Fixing is a very complicated sequence of reactions that changes the non-soluble silver salts in the emulsion into soluble compounds. This process proceeds rather rapidly in fresh fixer, but slows down as by-products from the fixation build up in the fixer. That means that the proper fixing time for your film and paper changes as you use the fixer. I'm not even going to get into the different kinds of fixer, rather just suggest you use a rapid fixer of some sort. The whole discussion of sodium-thiosulfate fixers vs ammonium-thiosufate fixers and alkaline vs acid or neutral fixers we can save for another day.
For film, a clearing test is good for determining fixing time, but keep in mind that the fixing time you find that way for fresh fixer isn't going to be correct after even a roll or two have been fixed in a given amount of fixer. There are a couple of strategies to deal with this.
1. Do a clearing test before each roll/batch of film to determine the clearing time. Double that to find the minimum fixing time for that particular roll or batch. Make sure you discard the fixer before the clearing time in used fixer reaches twice that in fresh fixer (you keep track of that initial clearing time in fresh fix for each film/fixer combination you have).
2. Given that fixing film longer than the minimum time it takes to be adequately fixed will do no damage unless it is really excessive (we're talking 10-15 minutes longer than needed), you can simply use a time that is equal to that for fixer that is approaching exhaustion. Exhaustion is when clearing time is 2x that in fresh fixer. Twice that would be the minimum clearing time for film fixed in this used fixer, i.e., 4x the time in fresh fix. So, you can simply do a clip test with a film and fresh fixer, find 4x that time and safely use that time until the fixer approaches exhaustion. You still have to do a clearing test to find when to discard your fixer. If you keep track of the throughput a few times, you'll be able to estimate the number of rolls/sheets you can fix in a given amount of fixer before you need to start testing. FWIW, I always use 4x the clearing time plus 10% and discard my fix well before it reaches exhaustion just to be on the safe side. When I'm processing large amounts of film, I use two-bath fixation, since it's a bit more economical (more later).
For paper, it is inconvenient to do a clearing test, so throughput is usually used as a guide to fixer capacity. Times are based on minimum time to adequately fix the paper in fixer that is reaching exhaustion. These limits are determined by testing. The manufacturers have done this testing and provided fixing time and throughput limits, but you can certainly do your own testing (I have). You need to test for residual silver in completely fixed-out areas of your print (i.e., unexposed portions of the print that should have no silver left in them after fixation). There are two easy and common tests for this, the Kodak ST-1 test and the similar test using Kodak Rapid Selenium Toner, or similar. I won't go into the details here, but it's easy to search for the tests, their components and how to use them. What you do is find the throughput of your paper/fixer combination that just starts to show inadequate fixation, then reduce that number and add a safety factor to arrive at a safe throughput for paper/fixer combination. Keep in mind when doing the test, though, that there can be a lot of variability in how much fixing actually has to happen from print to print. Prints with lots of white areas require more fixation and exhaust fixer faster that prints that are mostly dark.
Complicating paper fixation is the fact that there are two kinds of paper, RC and fiber-base. RC, or resin-coated papers are more like film in that the fixer doesn't soak into the paper base. Fixer capacities for these papers are different than for fiber-base papers. Fixing these papers longer than minimum isn't a big issue. Fiber-base papers, on the other hand, require fairly careful control of the fixing time, since fixing longer than needed allows the fixer to soak into the paper base, which makes it harder to wash out.
Further complicating matters with fiber-base paper is that there are a couple of widely-used strategies to deal with the above problem. One is Ilford's method, which consists of using a rather strong dilution of fixer for a short time. The idea is to get the fixing done before the fixer has time to soak all the way into the paper base. The time for most papers is 60 seconds in "film-strength" fixer. This works well for some, but is inconvenient for others. Ilford has lots of information about their methods online, so I won't go into them here.
Some, like me, use the older Kodak method for fixing fiber-base papers. This uses a more-dilute fixer for a longer time, but then needs a wash aid and a longer wash time to adequately wash the prints. Again, I'll let you search for the particulars.
Then there's one-bath vs. two-bath fixation for fiber-base prints. Two-bath fixation can be more economical, effectively doubling the capacity of your fixer, but you need a higher throughput to take full advantage of that. The idea is to give half the fixing time in one fixer, then transfer the print to a second fixer for the second half of fixation. The first bath does most of the work and can be used a bit past the point of exhaustion since the second bath will be very fresh and be able to complete the fixation without exhausting it much at all. After the throughput capacity for the first bath is reached, it is discarded. The second bath is then "promoted" to the first bath and a new second bath is mixed. This cycle can be repeated four to five times before both baths need to be replaced. This same method can be used with film and RC papers to economize a bit when throughput warrants it. For fiber-base paper, which requires more careful processing, it is more commonplace.
Keep in mind also that there are different "standards" for fixing paper depending upon the level of permanence you desire. There is a "general-purpose" or "commercial" standard that is aimed at prints that don't need to have optimum permanence. "Optimum-permanence" or "archival" standards ensure that prints are fixed to last for decades if not centuries. In order to do this, fixer capacity is more limited, which keeps even smaller amounts of unfixed silver compounds from remaining in the paper. Do read the Ilford document on their fixer products. It is quite informative. It is easily found online.
Testing: Careful workers keep track of their paper processing by using both a residual-silver test and a residual-hypo test. The former tests for adequate fixation, the latter for adequate washing. As mentioned above, the ST-1 test or the selenium-toner test is used for residual silver; for residual hypo (i.e., residual fixer compounds remaining in the paper), the HT-2 test is used. Again, formula and instructions are easily found online.
A word about overfixing film and paper. Overfixing, especially in rapid fixers, can bleach the image silver in both negatives and papers. However, this is not much of an issue with film, since it is rather tolerant to longer-than-minimum fixing. Many of us fix for longer than recommended just to get rid of some of the retained dye in the film base. Many papers are the same; a bit of overfixing won't hurt the image at all. With some warm-tone papers, though, one has to be careful not to fix too long or the image will begin to degrade. And, if one uses the Ilford quick-fix-in-strong-fixer method for fiber-base papers, one must keep to strict fixing time or the advantage gained in print-washing time will be lost.
Or, you can just use the manufacturers' recommendations
Best,
Doremus
