Quote Originally Posted by Michael R 1974 View Post
What is your reason for needing this? By the way you might want to try TF-5 which is very close to neutral.
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.

Unfortunately, shipping TF-5 to Ireland is prohibitively expensive, due to weight, and I cannot find it sold here...

Quote Originally Posted by Gerald C Koch View Post
The pH of an ammonium thiosulfate solution 60% is already between 7.5 aqnd 9 add to this the addition of sodium sulfite and you already have a buffered fixer without the need for any additional buffering.
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?

Quote Originally Posted by Rudeofus View Post
Before you load your fixer with all kinds of extra compounds, go read what "ionic strength" means and what that means to fixers. Long story short you can really slow down fixer action if you add too much extra stuff.
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.

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?