Michael, I should have explained my reasons, but I didn't want to bore anyone with the details of my current process, which I am aiming to optimise—tinkering to save time, I suppose, and to cut down on acetic acid fumes, though I don't want to replace them with plenty of ammonia, either, hence the desire to stay neutral, rather than alkaline. As Gerald points out, I believe I have no need for an acidic fixer, as I have no need for hardeners. Secondly, I tend to tone, in KRST, at the end of my printing session, sometimes twice in a day, and I would like to make that step even more immediate at times. Sine I tested, I know my current fixing is good, in terms of residual silver halides, so I should be able to dispense with, or shorten, the rinse prior to KRST, which is currently necessary due to the acid in the fixer, which Se does not like. However, I want to stay with a rapid fixer, hence ammonium thio in a neutral setting appeals to me. Finally, I am comfortable with a citric acid stop, and I want to continue using it, without pushing the fixer into acidic territory, hence my request for a suggestion of a buffer. For what it is worth, I fix twice, 45 s each plus 15 s drain time, and I like using the first fixer till it has about 3 g Ag/l, hence the safety net of the 2nd fixer bath to make the argentothiosulfates easier to wash out. I also use a sodium sulfite washing aid after KRST. In the long run, I am keen to experiment with removing the second fix bath, since I think the thiosulfate in KRST, and then a fresh washing aid, perhaps slightly prolonged from my current 3 min to 5 or so, may do a good enough job of getting rid of the fixing byproducts. But first, I just want to try with a neutral one.
Originally Posted by Michael R 1974
Unfortunately, shipping TF-5 to Ireland is prohibitively expensive, due to weight, and I cannot find it sold here...
Gerald, would you be able to estimate how many ml of citric acid stop would it take to bring 1l of a mix of (ammonium thiosulfate 120g + sodium sulfite 15g + sodium metabisulfite 5g) below pH 7, say to 6.5?
Originally Posted by Gerald C Koch
Rudeofus, thank you for your kind suggestion to read up on ionic strength. I have spend an hour or so picking up on the subject on Wikipedia, and I have browsed a Kodak patent that talk about this metric in the context of fixers. I will be reviewing Mees later today, to find out more, as I am just reading that amazing book. All I can understand, so far, is that increase in ionic strength will affect photographic material gelatin swell which may also reduce fixing rate. What I am unable to determine, however, is how significant would that effect be, especially with a buffer designed for the purpose.
Originally Posted by Rudeofus
Since you know about ionic strength issues in fixing, may I ask you, please, to estimate what would be the impact, in terms of how much I would have to extend fixing time when using a buffer such as 5g Borax + 5g Boric Acid in 1l of the fixer, such as the one mentioned above? Do you have any other suggestions as to where I should read more about ionic strength and fixers?