Ammonium Thiosulfate fixers and Acid Stop Baths. Good, Bad, or Indifferent?
I posted this question in another forum, but I thought I try asking here.
I noticed that my fixer (Agfa Universal Fixer) turns pink after a few printing sessions. When I checked the ingredients on the label, they are Ammonium Thiosulfate and Sodium Sulfite. From what I've read, both are neutral to slightly alkaline when aqueous. The Material Safety Date Sheet states that the PH is about 7.6 - neutral to slightly alkaline. I figured the pink colour is due to the Indicator Stop Bath being neutralized by the alkaline fixer. But doesn't that also mean that the stop bath is acidifying the fixer? I thought fixers like TF-3 and TF-4 where the only ones that were supposed to be alkaline.
So, given that one of the reasons to use an acid stop bath (when using an acid fixer) is to neutralize any carried-over alkaline developer, is it a good idea to use an acid stop bath, like Kodak's, given that this fixer is alkaline? Anyone know?
Fixers like TF-4, which are highly buffered don't care if you use a water rinse with running water, or if you use a stop bath. They are compatible. Unbuffered alkaline fixes prefer a running water rinse. Acid fixes don't care either way.
I'm no expert at this, but from what I've read (lots of really smart people hang out here) is that fixers like TF-3/4 are rather well buffered to absorb the acid from stop baths.
However, you'll probably get even more life out of the fix if no acid stop is used. I haven't used an acid stop in years. Once less chem to keep as well.
Ian, Bill Troop, PE, Kirk, et al can add much more to this thread if they latch on.
Your analysis sounds good to me, but who knows what might cause the pink color. As long as it doesn't color the prints, it's probably OK. You shouldn't have enough carryover from the stop to the fixer to matter. Even if the fixer pH did shift slightly (any shift is unlikely to be significant), the fixer will still work just fine. In any case it is wise to let the print drain pretty well before placing it in the stop bath and again before placing it in the fixer.
Use a water stop, agitate for 30 seconds, then into the TF-4...you'll have a totally alkaline process. You'll definitely get more life from the fixer this way.
Always make sure to drain the print as much as reasonably possible before immersing in the next tray...always a good idea.
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Originally Posted by Nick Kanellos
In the articles section on this forum you will find the "buffered stop bath" by Ryuji, this is the one I use with AGFA's FX-U (good stuff BTW). I use the second formula and add 5 gr to the NaOH (= 30 gr now) just to be sure the pH is above the 5.5.
Last edited by Philippe-Georges; 01-10-2009 at 05:31 AM. Click to view previous post history.
"...If you can not stand the rustle of the leafs, then do not go in to the woods..."
(freely translated quote by Guido Gezelle)
PS: English is only my third language, please do forgive me my sloppy grammar...
I'm rather more concerned by the phrase "I noticed that my fixer (Agfa Universal Fixer) turns pink after a few printing sessions." That sounds rather like overuse beyond it's recommended capacity.
I do use fixer for multiple sessions, never more than two or three, but only in a two bath sequence, so the final fixer bath is always fresh. Fixer builds up a level of bromide & iodide and becomes less efficient and even alkali fixers will suffer from the build up of silver. You really run a very high risk of images deteriorating in quite a short period of time.
Ilfords Hypam/Rapid fixer is designed for short wash times and has a pH of 5.2, alkaline fixers offer me only marginal if any real advantages except with some alternative processes. I always use an acid stop for fibre based papers as this really does help prolong the fixer life. If I used an alkaline fixer I'd look into using an alternative stop bath, as this would probably be better than a water rinse with FB papers.
The modern trend is to use a Citric acid/citrate stop bath and Japanese research (Fuji Patent) indicates this actual improves fixer efficiency. Ilfostop is of this type but it is actually more acidic than Acetic acid stop baths.
There are alkali stop baths available but they aren't common or made by any of the major manufacturers.
Good point. A help would be a few more details from the OP.
Originally Posted by Ian Grant
That acid Indicator stop could well go pink in an alkaline
solution. With little or much transfer I couldn't say. All
and all I believe indicators are by nature very quick
to indicate. That is, minute amounts of indicator
will show. Dan ----- PS: a PM soon.
My own preference is no indicator at all in an acid stop-bath, it's relatively easy to tell when the acid has been neutralises, and in practice they have good capacity anyway.
If an acid indicator is causing a pink colour in an alkaline fixer it may well be indicating that stop-bath carry over has altered the pH and so it's no longer alkali. It's also indicating overuse.
I have tested indicator stop baths in alkaline solutions to see if they cause any retention of color in paper, and my tests show no retention at all. Now, this may vary with some FB papers, but the strong indicator does wash out in the wash step. It is very soluable.
The current Kodak indicator turns from slight yellow to dark purple. This is the only stop I currently use except for 2% acetic acid.