It's strange that people talk about proprietary formulae of Ilford and EKC, but not the small company...

I just found on my old copy of "The Darkroom Cookbook" by Anchell that the pH of T-F4 (I guess it means TF-4) is 6.0 on page 37. This is not really alkaline to many people but that's ok. Did anyone confirm this pH? Incidentally, when I checked the pH of Ilford Multigrade fixer (working strength) the pH was at 6 range. I think at pH of 6, thiosulfate is easy to wash off because the pH is higher than gelatin's isoelectric point.

Ilford list sodium acetate and sodium bisulfite in the list of multigrade fixer's ingredients, and the pH seems buffered. One may want buffer the pH because pH too high may result in strong odor and too low may result in conventional acid fixer that requires long washing. Ok, it makes sense... What does TF-4 uses to buffer pH? (anyone thought about it?)

So, assuming that Anchell was right, how is TF-4 superior to Ilford Multigrade fixer, which is sold everywhere?

Finally, did anyone try to formulate own neutral pH rapid fixers?

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), July 01, 2001

Answers

In the second edition of The Darkroom Cookbook, Anchell lists the pH of alkaline fixers as between 8.5 and 9.5 on page 44 (under pH scale). He notes in the preface that one purpose of the second edition was to correct a number of minor errors in the first edition. Perhaps this was one.

I have made TF-3, from the second edition. It uses sodium metaborate as a buffer and has an ammonia smell. TF-4 reportedly has a "secret ingredient" which gives it twice the fixing capacity of TF-3 and less smell.

-- Brian Hinther (brianh@onewest.net), July 01, 2001.

What is the fixing capacity of TF-4? (do they give a specific number as a guide?)

I guess the pH of TF-4 must wait until someone measures it. (I'd greatly appreciate if someone could dip in a pH indicator strip. I don't need accuracty to 1/10 of pH...)

If TF-3 smells because of high pH, it seems that the next step is to lower the pH a bit. Perhaps by adding some sodium metabisulfite or sodium bicarbonate (baking soda)... this is something I can easily try...

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), July 01, 2001.

An update.

I was unaware of dead stop bath for a while (it's hard to see the indicator's dye color in slot processor - I'll switch to non-indicator stop bath and use pH indicator strip instead), and I noticed ammonia smell from my Ilford Multigrade fixer. I dipped in a pH indicator and it read about 7.5. This fixer has been used a little less than half of Ilford's published capacity.

If the ammonia smell of ammonium thiosulfate fixer is primarily depending on the pH value but not so on other factors then it is probably pH of 6 that one wants the fixer to maintain... but it would be nice if I could avoid sodium acetate... maybe lots of boric acid...

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), July 17, 2001.

I guess this is drifting from the thread of the original query but i just wanted to say thanks to all of you for discussing this, as it gives me some much needed background.

I have used pmk pyro for years now but want to use TF3 fix since it is recommended for use with pyro, maintaining an alkali environment and so on. I recently came accross the formula for TF3 and TF2. I looked at the price of Amonium thiosulphate and noticed that it was much higher than that of sodium thiosulphate. However the formula for TF2 (Sodium thiosulphate..)does not list a dilution from stock (the initial 1 ltr mentioned in the formula..?) to working solution, so asuming it is used at this initial strength, it actually works out slightly more expensive than the TF3 (given the dilution and capacity figures in the formula..). So I decided I would order some amonium thiosulphate and get on with some work.

However my intention was to order 5 kg of it, but I then came accross the comments saying that it is not very stable in dry form.

Any thoughts on this would be appreciated.

Many thanks. Oh I forgot to mention that I do not want to order TF4 from 'The formulary' as I live in the U.K and it would cost silly money for the shipping, hence my exitement upon finding the TF3 formula along with a note stating that it is more alkaline than TF4 anyway..

-- Neil Tribe (neil@tribe44.freeserve.co.uk), October 28, 2001.