Acid Stop Bath with Ammonium Thiosulfate fixers. Good, Bad, or indifferent?

[Nick Kanellos]

Before Agfa went under, I stocked up on their Universal Fixer. The label indicates that the ingredients are Ammonium Thiosulfate and Sodium Sulfite. From what I've read, both those compounds are neutral to alkaline.

So, given that one of the jobs of an acid stop bath is to neutralize any carried-over alkaline developer, and prolong the life of the fixer; does it make sense to use an acid stop bath, like Kodak's Indicator Stop Bath, if both the Developer and the Fixer are alkaline?

I ask, because I noticed that the alkaline fixer turns pink after a few printing sessions. I suspect it is the alkaline fixer that is neutralizing the carried over acid stop bath and causing the indicator to change colour. But doesn't that also mean that the acid stop bath is neutralizing the alkaline fixer? Am I degrading my fixer prematurely?

Does anybody know?

[Steve M Hostetter]

I use acid bath because it helps keep the film tube clean ,,, I've tried just using water but when I went to clean the tube my cloth I used to dry it with became black ...
I think the cleaner the tube the better results you'll have with processing..

[Don7x17]

Before Agfa went under, I stocked up on their Universal Fixer. The label indicates that the ingredients are Ammonium Thiosulfate and Sodium Sulfite. From what I've read, both those compounds are neutral to alkaline.

So, given that one of the jobs of an acid stop bath is to neutralize any carried-over alkaline developer, and prolong the life of the fixer; does it make sense to use an acid stop bath, like Kodak's Indicator Stop Bath, if both the Developer and the Fixer are alkaline?

I ask, because I noticed that the alkaline fixer turns pink after a few printing sessions. I suspect it is the alkaline fixer that is neutralizing the carried over acid stop bath and causing the indicator to change colour. But doesn't that also mean that the acid stop bath is neutralizing the alkaline fixer? Am I degrading my fixer prematurely?

Does anybody know?

Nick
The acid stop bath is there to instantaneously stop development -- the change in pH does that. there are many good books that will give you more detail. You can easily get by with just a few ml of glacial acetic acid in water. And no pink dye from the indicator made by kodak or others. Its cheap -- just discard after use. No need to wonder whether its "exhausted", which is why the indicator is used.

With regards to your fixer turning pink -- have you looked at the manufacturer's recommendation on fixer usage, usually stated in square inches of film? Plan for discard long before any iodide-based test solution drop turns cloudy in the fixer - by this time you're fixing in a soup that has residual silver compounds which can be difficult to wash from the film.

And if you are really concerned about dye carryover from using an indicator stop bath, you can always do a quick water wash between stop bath and fix -- it won't hurt a thing.

[J D Clark]

Nick,
You are correct, neutralizing the alkaline developer with acid stop to then go into alkaline fixer doesn't make any sense. With an alkaline fixer you should just use plain water for your stop bath. The web page on Photo Formulary for their TF-4 fixer indicates you don't need stop at all, presumably meaning that you could go from developer into fixer. When I used TF-4, I used a water stop bath.

Ultimately, I found the slight ammonia smell of alkaline fixer more disagreeable than regular fixer, so I went back to regular acid fixer, with an acid stop.

John Clark
www.johndclark.com

[David Vickery]

Are you certain that Am. Thio. and Sodium Sulfite are the only two components of Agfa's Universal fixer? I don't know because I have never used that fixer before, but most "universal" type fixers (pre-mixed) that are based on Ammonium Thio. are acidic because of the addition of Acetic acid, plus they usually have other components as well.
Ammonium Thiosulfate works whether its in an alkaline fixer or an acidic fixer. So I doubt that an acid stop bath would prevent the fixer from working. You do not need to use an acid stop if you don't want to, but as stated above, the acid does stop the development faster than plain water. I would recommend a water bath between the Developer and fixer.
I process film and paper in trays and have found that the most pleasant way for me to work is to use a large tray of water with a small amount of citric acid added (~half to full tablespoon depending on the amount of water) and an alkaline type ammonium thio. based fixer that I mix myself and also add a little citric acid to it--I would do the same with sodium thio. based fixer as well. The citric acid is much more pleasant than acetic acid and prevents the bad aromas. I use a little more citric when I am processing paper and less when processing film, especially if using a pyro based developer.

[Nick Kanellos]

Are you certain that Am. Thio. and Sodium Sulfite are the only two components of Agfa's Universal fixer? ...

Dave, you are correct. According to the MSDS, there is an additional component not listed on the label: Ammonium Hydroxide. The complete list of ingredients is:

AMMONIUM THIOSULFATE ---------Fraction by Wt: 45-50%
AMMONIUM HYDROXIDE -----------Fraction by Wt: 1-5%
WATER-------------------------Fraction by Wt: 35-40%
SODIUM SULFITE----------------Fraction by Wt: 10-15%


All are alkaline (except the water:) ). I should note that I replaced the fixer with a plain water bath, and the fixer no longer turns pink/purple. Clearly it was the alkaline fixer activating the carried over indicator dye from the stop bath, as I suspected.

As for whether an acid stop bath is adversely affecting an alkaline fixer, I'm told that "it depends." I suspect that the sodium sulfite is acting as a preservative (true?). The acid may be prematurely "aging," as opposed to exhausting, the fixer by neutralizing its preservative components.

One thing I noted by moving to a water stop bath. Replace the water often to avoid build up of developer. Otherwise your stop bath -- ain't. The other thing to note is that one should NOT turn on the lights as soon as the print is in the fixer, as was my practice before. A water stop bath is not really neutralizing anything. It is simply diluting/washing away the developer. That will not happen fully in the 30 sec to 1 min commonly spent in the stop bath. Especially for FB papers. You will get unwanted density since the alkalinity means that there is still developing action occuring by any residual developer. Now I wait for 1 minute before turning on the lights. After a few wasted sheets, that is.

Thanks for all your help.

[Drew Wiley]

Replacing an acid stop bath with plain water often creates a secondary issue of changing the way the developer itself continues to work. So in order to avoid carryover of acidity into the fixer, I sometimes simply use a plain water rinse AFTER the stop bath. Just one more simple step.