Ammonium Thiosulfate fixers and Acid Stop Baths. Good, Bad, or Indifferent?

[Nick Kanellos]

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?

 

[Photo Engineer]

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.

PE

 

[jim appleyard]

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.

 

[nworth]

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.

 

[PVia]

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.

 

[Philippe-Georges]

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?

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.

Good luck,

Philippe

 

[Ian Grant]

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.

Ian

 

[dancqu]

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. Ian

Good point. A help would be a few more details from the OP.
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.

 

[Ian Grant]

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.

Ian

 

[Photo Engineer]

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.

PE

 

[Kirk Keyes]

I find my Ilford Hypam fixer is slightly pink after using Tmax film. The color fades with time. I assumed it dye from the film, and nothing to do with the actual fixer.

 

[fschifano]

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?

I use a similar fixer, Kodak's C-41 Flexicolor Fixer and Replenisher and have noticed the same thing, but I never gave it a second though. After passing a few prints through the tray, the fixer picks up a decidedly blue/violet color, caused no doubt, by the indicator dye carried over from the stop bath. The fresh working strength fixer has a ph of 6 to 6.5, making slightly acidic, but not acidic enough to keep the dye from changing color. This is not a problem, and the dye will not stain the prints. It will wash out completely. The fixer itself is well buffered, and will maintain it's ph level for a good number of prints - probably more than is consistent with good archival practices. Eventually though, it will start to turn yellow and that's when you'll know that the buffering capacity has been exceeded. An acid fix with hardener, like the powdered sodium thiosulfate Kodak Fixer, will turn yellow after a few prints have gone through. It is acidic enough to maintain the yellow color of the dye.

Yes, it is a good idea to use a stop bath. The fixer should be buffered well enough to tolerate the small amount of acid carried over from the stop. Carrying active developer over into the fixer will shorten the life of the fixing bath, and may cause some staining on the print.

 

[Patrizio]

I currently use a Citric Acid based stop bath and a neutral fixer both from the same manufacturer. The life in the darkroom now is better. I don't tollerate any more the bad smell from Acetic Acid based products. Anyway I take the habit to cover the trays to reduced bad smell at a minimum level.
Regarding the prints, all fiber based, they don't seem to have any problem.

Patrizio

 

[Ole]

If the indicator used in the stop bath is Bromophenol blue, it should be blueish purple even in weakly acidic solution. Phenol red is another candidate, but that needs an alkaline solution to change colour properly which doesn't seem to be the case here.

Personally I can't see the logic behind putting any kind of dye in a stop bath, but then I use either water or a weak solution of citric acid for stop bath. Both are cheap enough to discard after use.

 

[Photo Engineer]

Flexicolor Fix is about pH 6.5 and is not alkaline enough to cause a substantial shift in the indicator color of a stop bath. I have not tested this particular combination, but it should not cause a problem even with a shift.

Also, the absorber dyes in film contribute to coloring the solutions, so if it happens with film and not with paper, it is the film that is the problem.

PE

 

[Ian Grant]

Flexicolor Fix is about pH 6.5 and is not alkaline enough . . .
PE

As Neutral is pH 7 then technically Flexicolor Fix is acidic

Ian

 

[Photo Engineer]

Ian;

Of course it is. But not all indicators shift at 7. So......

PE

 

[Ole]

Phenol red then, or possibly Bromocresol purple.

 

[Nick Kanellos]

I currently use a Citric Acid based stop bath and a neutral fixer both from the same manufacturer. ...

Patrizio

Patrizio, I'd be interested to know who the manufacturer is.

 

[Photo Engineer]

I would like to warn everyone who uses either a neutral stop or a standing water rinse with an alkaline fix, that the film or paper may fog in the fix itself if you turn the lights on too soon in the fixing cycle. The water rinse must be running water, not standing, and alkaline or neutral stops are just not strong enough to stop development in alkaline fixes, especially with extensive use. They exhaust very rapidly compared to running water or acid stops.

Therefore, you must not turn on room lights until 2x the clearing time has been reached or you will likely see some fog. I have run this experiment myself and seen a significant dmin increase in prints with standing water.

What happens is that with standing water, it gradually becomes alkaline with just a tad of developing agent build up. With running water for a rinse, this problem is eliminated. This is explicitly stated in TF-4 instructions. Use running water. The same is likely true of neutral or alkaline stop baths.

PE