Fixing paper: how long?
I've been making my own paper fixing solution from bulk sodium thiosulfate and sodium sulfite for some time now. I love using the bulk raw chemistry as unlike commercial products I have no immediate concerns of it being suddenly discontinued. It's also super easy with only two components. The other great advantage is I only mix it up as needed, so the chemistry is always absolutely fresh and new.
The disadvantage with homemade chemistry is I don't have any solid information on time, dilutions, strengths or capacity. There are no handy package instructions.
Looking at the processing recommendations from various paper makers isn't necessarily useful. They all say to use their own brand of chemistry--and then the fixing times and dilutions vary among the manufacturers.
So, for my homemade fix how can I go about finding or testing its limits myself? Of prime concern to me is the fixing time. I don't want to fix too short a time (30 seconds), nor do I want to unnecessarily fix too long (ten minutes) either. This will be for fiber-base paper.
I do want to find an adequate and well sorted processing regime for "archival" (an oxymoron) black and white printing. Going through the considerable time and expense of darkroom work and not following up on good processing is foolish.
Any suggestions for homemade fix?
You can test for residual silver with selenium toner. Don't have the particulars close at hand, but I think there are some threads in here that cover the method.
10 minutes for sodium thiosulphate would be a safe bet, seems to be a consensus. I always use rapid fixer and fix paper for 2 minutes as I feel that the less time in the fixer the easier it is to remove in the wash.
Fixing paper especially fibre base for longer than 2 minutes will mean it will take hours to get rid of the residual chemicals unless you use a 'fixer neutraliser' as an extra bath after initial wash. 2 minutes in fresh fixer for paper will be more than adequate. 'Bin doing it like that for 50 years and had no problems yet.
I fix mine for a minute in rapid fix and hold it in water bath. Then I fix it in a fresher batch of fixer for another 5 before I wash. I like the 2 fix bath method.
Ilford Hypam 1:4 for 1 minute as per Ilford's recommendation. http://www.ilfordphoto.com/Webfiles/201142795282272.pdf
Thousands of prints, never a problem.
Ladies and Gentlemen,
Originally Posted by konakoa
Let's try to read more carefully and give relevant advice. The OP is using a plain sodium thiosulfate fixing bath, NOT rapid (ammonium thiosufate) fixer. Therefore, suggestions using times for rapid fixers are irrelevant and, in the worst case, misleading.
To the OP: Two things come into play here. First is the actual fixing capacity of the sodium thiosulfate, second is the degradation of the fixer over time from oxidation, etc. One of the reasons fixers like Kodak powdered fixers (F-5) and other formulae have other chemicals in them is to keep the fixing agent itself from degrading. A plain "hypo" fixing bath like you are using does not have much of a lifespan time-wise. That means, use it quickly and discard it.
Now, as for times; if you want optimum permanence, use two-bath fixing. Fix 3-5 minutes (Kodak recommendation for F-6 IIRC) in each bath. Capacity is approx. 40 8x10 per liter of bath one (which means you have a bath two of equal size you are not considering). After reaching capacity, discard bath one and replace it with bath two. Mix a new bath two. I would start in fresh fix and the shorter time and gradually increase it to the longer over the life of the fixer. Alternately, you could just standardize on five minutes in each bath and make sure you give an adequate wash sequence.
Since you are using a plain hypo fixer, I wouldn't recommend using the solutions for more than one session. This means one working day and no more. Do use an acid stop bath with a thorough drain before the first fixing bath.
And, since throughput is only an approximation of fixing capacity, you will have to test your own workflow for adequate fixing (residual silver test) and adequate washing (residual thiosulfate test). The most common way of doing this is to use the ST-1 (residual silver) and HT-2 (residual thiosulfate) tests. Look at the Unblinking Eye website page on archival processing for more detailed info: http://unblinkingeye.com/Articles/Ar.../archival.html .
I test the last print in a fixing batch with both solutions every few batches to make sure my process is working correctly. With your home-brew fixer, I'd recommend doing both tests on every batch, pushing to the extreme for a while in order to determine your processing limits, then pull everything back leaving an adequate safety margin. This can then be your fixing regime and you can then test only every several batches as I do as a process control.
You should be aware that using a sodium thiosulfate fixer instead of a rapid fixer based on ammonium thiosulfate will require longer fixing times and, therefore, longer washing times with fiber-base paper. With this process, the use of a wash-aid such as Kodak's Hypo-Clearing Agent is indispensable. Since you have bulk chemicals handy, you can easily mix your own from sodium sulfite and sodium metabisulfite. There are many formulae in cyber-space; just Google. You may also be interested in more sophisticated fixer formulations, especially since they will last longer. I used the Kodak oderless F-6 formula for years. Nowadays, hardening fixers are used much less, so there are likely some better formulations out there. APUG is a great resource and there are many other resources on the web as well.
Hope this helps,
Thank you to everyone who has responded! Special thanks to Doremus for his detailed and very useful post.
I have actually used selenium toning as a casual indicator of the quality of paper processing. If the paper stained or had mottled areas in the toner it was a rough indication of something wrong in the earlier processing steps. However, this isn't something I'd want to always rely on--I'd rather be certain of the quality of my processing rather than guessing.
So another question--I've ordered one of the residual silver test kits from Photographer's Formulary. It uses sodium sulfide as the test agent. To anyone who has used it or something similar before, how reliable is this test?
My intention is to take my plain sodium thiosulfate fix solution and fix strips of paper for 30 seconds, 1 minute, two minutes, five minutes and ten minutes in the homemade fix. Then test each strip with the kit and see at what point the paper was fully fixed; then add just a bit more time to the indicated fully fixed strip as a safety margin. (That's the advice for film anyways.) Sound reasonable?
You're welcome. Here's a bit more :)
Originally Posted by konakoa
The Formulary residual silver test kit is the same formula as the Kodak ST-1. It is fairly reliable but not quantifiable, i.e., you don't end up with a value, just a subjective evaluation of staining. I've always erred on the side of caution and took any extra staining at all from an obviously well fixed and washed print to mean inadequate fixing. Read the page I linked to at Unblinking Eye for more info.
As for your suggested test procedure... Sorry, that will only give you a fixing time for the first print. As the fixer is used, the time needed for adequate fixing increases. When doing clip tests for film, you should test used fixer for clearing time (in essence what you are suggesting to do with paper) before each batch. This is impractical for paper. Just use the 10-minute guideline and the throughput as a starting point and test to find your practical capacity.
If you wish to process for optimum permanence, then I really suggest you use two-bath fixing, as I detailed above, and then test for both residual silver and hypo. (The residual hypo test only tests your washing sequence; you can have well washed but underfixed prints, and vice-versa. Really, testing washing is a separate thing, so I'll not address that completely from here on out, but you should do the test to find the efficiency of your wash sequence).
I would test as follows to establish a base line for your particular situation. Test the first print through the fixing and washing sequence. You should leave adequate borders on the print or simply fix and wash a blank sheet of paper. This sheet will certainly have been fixed well if you give 5 minutes in each bath (and, if you use a wash aid and wash for minumum 60 minutes in a good washer, should be washed well). This will serve as a control.
Then, after the recommended fixer throughput has been reached (approx. 35-40 8x10/liter), start marking prints for testing again. Mark you prints so you can keep track and test every few extra prints, say every third one, till you start getting test results that show residual silver.
Now you have an idea of the total number of prints you can fix in a given amount of solution. Keep in mind that this number is far from absolute. If the next batch has less developed silver in it (i.e., more undeveloped halides = lighter areas in the print) then the capacity will be much less. So, use your data as a guide and build in a generous safety factor. And, if there is any question if your fixer is performing well, test again.
And, after you have found a print that shows residual silver, refix it and the last several prints before it in the sequence in fresh fixer and rewash.
Now, if you wish to use single-bath fixing, you will find that your capacity is greatly reduced. Ilford says that for optimum permanence, only 10 8x10 prints per liter can be fixed (as opposed to 40 for two-bath fixing). Your residual silver tests will confirm this. Unless you really have a reason not to set up the extra fixing tray, use two-bath fixing for fiber-base prints!