Alkali Fixers - The Myths & Legends

[Ian Grant]

Over the past 7 or 8 months I've been looking at various fixers, Alkali and Acid.

So far I've not found any conclusive research that shows Alkaline fixers are actually beneficial for B&W processing.

I have found people who have used densitometry etc to show mildly acidic (pH 5.2-5.5) fixers like Hypam/Ilford Rapid fixer have no detrimental effect on negatives developed in Pyro developers (Pyrogallol & Pyrocatechin).

But I can't find any evidence that they genuinely reduce wash times either.

So can someone point me to the research findings ?

Ian

[Photo Engineer]

Ian;

No published findings that I know of except for the work by Haist and work I did at EK which is for the main part unpublished. I can back up most of the assertions on alkaline and neutral fixes as well from work I have personally done. As pH goes up, swell goes up (with bone gelatin) and washing becomes easier. As pH goes down wash slows down until you get to pH 4.5 where washing is most difficult.

As pH goes up, stability goes up, as pH goes down, stability goes down until you can actually destroy fixer instantly by adding a drop too much acid.

As pH goes down, you can add swell inducers to counteract the effect of the pH on swell and get more rapid washing.

I have verified this both at EK and at home, but remember that these are generalities and apply to bone gelatin, not pig gelatin. IDK about Yak gelatin.

PE

[sjg]

I've held off from mixing my first pack of PMK pyro 'cos I've not got a fixer with 'suitable' pH, so would be very interested in finding out if the stain won't disappear upon contact with my Ilford Rapid...
Simon

[Ian Grant]

What about the Llamas

But if you use a HCA you over-come the swell/shrinkage issue anyway, perhaps this was why Agfa recommended Sodium Carbonate as the HCA for their Fibre based papers.

I can see there's a definite problem with acid hardening fixers at pH 4.3, but then something like Hypam at pH 5.3 shouldn't be much of an issue. I've seen the pH of TF-4 reported to be 6.5, hardly alkaline !!!

Ian

[Photo Engineer]

TF-4 is more like 8.

PE

[ntenny]

Gee, Ian, what prompted this question? :-)

I give up---I'm just going to accept that I don't understand anything, and sit back and wait for you experts to sort it out! (Personally, I'm more concerned about the washability than the putative pyro problems.)

-NT

[Photo Engineer]

At any pH from about 6 - 9 a wash aid is often not necessary as the wash speeds up so much due to swell. It depends a lot on water supply (hardness) and paper or film hardness as well as the thickness of the coated layer. That is why I suggest testing to everyone to establish their best position.

PE

[Ian Grant]

So your saying that a fixer of say pH 5.3 will be fine then, after all as soon as you start washing the pH will change. But then wash aids aren't just about gelatin swell and are used to tip equilibrium balances, particularly of the partially soluble silver-thiosulphate complexes. But we could help the water supply by ensuring it's mildly alkaline early in the cycle ?

Gee, Ian, what prompted this question? :-)

I give up---I'm just going to accept that I don't understand anything, and sit back and wait for you experts to sort it out! (Personally, I'm more concerned about the washability than the putative pyro problems.)

-NT

Nothing you've said/written Just something I'm curious about, as all the hype about TF-4 seems contradictory.

Ian

[Photo Engineer]

I've found that water hardness is more significant than pH when it comes to water supply, but again that is a generalization. Wash aids can actually decrease swell due to the salt effect if concentration is off. Too high and swell goes down.

The silver thiosulfate complexes (about 5 of them) are huge, but the ammonium silver thiosulfate complexes are considerably smaler and there are other agents that can be inserted into the complex "cage" to change ionic attraction, size and diffusion rate. Thiourea comes to mind here. It is smaller than thiosulfate and so like ammonia can increase diffusion rate and also it is synergistic with hypo increasing fixing rate. Being non-ionic, thiourea helps in other ways too. Or at least it changes the playing field.

So, there is no one answer Ian. There are many many doorways and mirrors all over this room. Many of them do NOT lead to wash aids of any sort. And that is a very important point. I can increase wash rate by about 50% just by manipulating the fix, and this is in comparison to TF-4.

PE

[David A. Goldfarb]

I've measured the pH as 8 for fresh TF-4.