I stated before that salt will not fix photographic film, but I was wrong. Yes, I tested it and it didn't work, but under special circumstances you can use kitchen salt as a fixer. So how to?
You must use a highly concentrated solution of table salt of about 300 g/l. That's a lot! That's really a lot!!! Maximum solubility is 359 g/l, so the suggested solution is almost saturated and the diluting process takes some time and/or a lot of stirring. Furthermore the fixing takes a lot of time, after about 24 hours the exposed at room light but undeveloped little piece of APX100 was clear. Since fixing time is said to have to be doubble of the clearing time, expect a total fixing time of 2 days! Rising the temperature to 30 or 40 °C will shorten the time to a couple of hours, but I don't want to "cook" my bw-films.
The perfect clear snippet of the film then was developed and no blackening at all occured, indicating that no silver halide was hold back in the emulsion. I developed with Caffenol-C-M and the film snippet got a remarkable brown tint. I noticed before that some films have a stronger brown tint if they are developed with salt as a restrainer, of course with much less salt. But of course usually the negs are first developed and then fixed, so I expect no problems.
I tried regular non-iodized table salt and iodized table salt, both work about the same. Both contain a small amount of anti-caking agent: E 535 aka hexacyanoferrat(II). Since the amount is very small - max. 20 mg/kg - I don't think it has an influence. But never say never again, hahaha.
So it's good to know that there is an alternative to thiosulphate based fixers. Be it if you live abroad or can't get regular fixer for what reason ever or simply because you like it, it's good to know. I will continue fixing with the regular one because it only takes a few minutes, but NEVER SAY NEVER AGAIN.
All these insights I owe Sir Henrique the "Cronocrator" and his fine blog: http://caffenolcolor.blogspot.de/ and the corresponding discussion in "the new Caffenol home" group at flickr. Thank you very much, guys.
Some questions are left, f.e. we have no explanation why it works and how other films behave, especially films like TMax or Delta. So before using this method you should make own trials with the film and salt you use before you ruin important negs. It's simple. Cut a small piece from the leader of 35 mm film, put it in a solution of 300 g/l salt, wait and see. Should be done in a simple glass mug.
Now after so much salt I urgently need a COFFEE!!!
Best - Reinhold