Can too long a fix time damage a negative?

Hi folks. Sorry for the silly noob question.

I'm using 5 min fixer time for 35mm with Ilford's rapid fixer @ 20C.

Today I was just wondering to myself:

"self, is it possible to damage a film by over-fixing?"

So I decided to ask here: know of no better place.

Is there an upper boundary for fixer time beyond which an emulsion will be adversely affected?
If so, how, why and how long?

I'm not too fussy with my 5min: picked it after doing the usual test - cut the end of a film, dip it in the fixer, check how long it takes to clear, then double that time. That's 4 minutes for most of my film, so I use the 5 recommended by Ilford.


TIA for any replies

It certainly can, but 5 minutes or even 10 minutes when the fixers been used more heavily isn't long enough to damage the film, and you've still got a little more leeway.

I can't say how long is too long, film emulsions are more resilient than paper emulsions, but with warm-tone papers over fixing in fresh fixer will rapidly lead to some bleaching of the prints highlight. And if left far to long will dissolve all the silver out of the image.

Ian

Ian Grant said:

It certainly can, but 5 minutes or even 10 minutes when the fixers been used more heavily isn't long enough to damage the film, and you've still got a little more leeway.

I can't say how long is too long, film emulsions are more resilient than paper emulsions, but with warm-tone papers over fixing in fresh fixer will rapidly lead to some bleaching of the prints highlight. And if left far to long will dissolve all the silver out of the image.

Ian

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I thought I read somewhere recently that it depends on the PH of the fixer? i.e. Acid fixers don't bleach or at least it is much reduced whereas alkaline fixers bleach more. I could be wrong about this but am interested in more info on it.

I could be mistaken, but I think it is the other way around. Acid fixers can bleach an image in less time. But it hardly matters. It takes a while for this to happen to any appreciable degree, and your 5 minute fix times are far below that. Don't worry about it and pay more attention to the important stuff like temperature control, consistent agitation, and clean working habits.

It's more of an issue with Ammonium Thiosulphate based fixers, and they are rarely particularly acidic, so Hypam/Ilford Rapid fixer has a pH of 5 -5.5 in use, Hypam 4.5 -5 with an acid hardener.

Any fixer will bleach highlight details if left too long, regardless of pH. But as I said films quite resilient and with warm-tone papers the bleaching can take as little as 5 minutes in fresh fixer to become just noticeable.


Ian

I'm not sure about the pH factor. I have seen ammonium thiosulfate fixers bleach prints and attack the shadow areas of negatives. The more concentrated fixers (such as X-ray fixer) do it faster, sometimes in less than 10 minutes. I have not seen it happen with ordinary sodium thiosulfate acid fixers, but given enough time, I'm sure it would. Temperature also has an effect, I'm sure. The Ilford recommendations may be a bit short, but they have the right idea - fix for the shortest time that does the job. The required fixing time depends on the emulsion and its construction, and you can't always tell what is needed by visual inspection. As a rule of thumb, twice to four times the time it takes to clear is pretty good. T-grain films, which are harder to fix, may be at the long end of that figure; fine-grained ordinary films at the short end. You can test the effectiveness of fixers, but the sensitivity of the tests may be questionable. The effectiveness of the fixer also decreases with use, as silver products build up in the solution. It is important to use fresh fixer to get consistent, short fixing times.

You make a very valid point fixers really do vary, I went from making emulsions in the 70's/80's to precious metal recovery - Xray fixers can can have a ferocious appetite for silver, we'd regularly test them and find very high silver contents 10-15gms /liter.

It's very important to use a fixer as it's manufacturer recommends. That way you have no problems.

ian

Ian Grant said:

Xray fixers can can have a ferocious appetite for silver,
we'd regularly test them and find very high silver
contents 10-15gms /liter.

It's very important to use a fixer as it's manufacturer
recommends. That way you have no problems. ian

Click to expand...

Ilford mentions 8 to 10 grams as a limit for film fixers.
I don't believe that is an 'archival' limit. G. Haist, IIRC,
has listed film fixer silver load limits.

If some degree of precision were wished then the exact
load limit would depend upon the film; the film's mix of
chloride, bromide, and iodide. Same for paper.

Haist does not mention limits by film. It is general
knowledge that iodided films require more fixer;
a lower load limit. Dan

Doesn't surprise me to hear that about x-ray fixers. They are designed to work fast. X-ray processing machines do a sheet of double sided emulsion from dry to dry in only a few minutes. I've not tried using any of these fixers for photo work. If they are cheap enough to buy, I might and dilute it to half, or even 1/4 the standard working strength to see how it goes.

X-ray fixers aren't particularly different to standard fixers, some are hardening fixers to help protect the emulsion at the higher processing temperatures. The processing machines work on a topping up replenishment system so the amount of silver per litre really depends on how fast that rate is. The sales/service engineers would turn up the replenishment because that meant they sold more chemistry, our engineers would turn the rate down because it was more cost effective to take spent fixer with a higher silver content for Silver recovery and then disposal.

Ilfords 8-10gm Silver per litre level is fine for film fixer because the unstable silver - thiosulphate complexes formed wash out easily from the emulsion layers. However with fibre based papers these unstable complexes attach themselves to the fibres of the paper base itself and can't be washed out, so it's far more important to keep the silver content lower, and the two bath method of fixing is the most efficient way of ensuring archival permanence. Resin coated papers are more like film and can stand a higher silver content with no problems.

Ian

Not if you are shooting t-max