Fixer 101 (?)

Hi everyone,

(tl;dr: I want to learn about all the different types of fixer and how to tell them apart.)

I currently use Zonal Pro (by Alta) Extended Capacity Rapid Fixer. Sadly, this is a company that has shut its doors in the past few months. The bottle says it contains both Ammonium thiosulfate and acetic acid. Now, I know that the ammonium thiosulfate—as opposed to sodium thiosulfate—makes this a rapid fixer. But I had also heard somewhere that ammonium fixers were alkaline fixers...? I remember from Steve Anchell's Darkroom Cookbook that alkaline fixers had many advantages over acid fixers. I then read somewhere else that alkaline fixers were simply non-hardening fixers.

Basically, my questions are:

1) Is there a way to tell—beyond litmus testing—whether a particular fixer is acidic or alkaline?

2) I'm thinking, based on the advantages listed in TDC, that I would like to try an alkaline fixer. However, all that's mentioned is the Formulary's TF-4. Are there other commercially available alkaline fixers? Do they work for paper processing as well as film?

3) What's the deal with hardeners? Do they change the pH of the fixer? I occasionally want a hardening fixer for films like Efke 25, and it would be nice to just add a secondary step rather than mix up a whole batch of Kodafix, which doesn't last at all.

I'll leave it at that for now, since I'm sure all your answers will only raise more questions.

1) not really
2) TF-4 works for film and paper and is the only one I am aware of that is truly alkaline.
3) Hardeners only work and acid fixer, or at least I have only seen in acid fixer.


Let me say that there is a lot of confusion about fixer.
there are acid fixers and alkaline fixers
there are sodium thiosulfate fixers and ammonium thiosulfate.
all alkaline fixers are ammonium thiosulfate, but not all ammonium thiosulfate. are alkaline.
BUT often ammonium thiosulfate fixers are considered to be alkaline even though the pH is well under 7
Ammonium thiosulfate fixers are rapid.

With modern films and paper hardeners are not generally needed.

Alkaline fixers have some advantages, there are others here that can better describe them better then I. The biggest advantage is that ammonium thiosulfate fixer are that they are fast and there is a pH range that ammonium thiosulfate can achieve that easy promotes washing.

yeknom02 said:

1) Is there a way to tell—beyond litmus testing—whether a particular fixer is acidic or alkaline?

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Yes. Get the name of the product and post a question right here on APUG.

Concerning the hardener, it is my understanding that modern film and paper do not require it. I was told, the hardener must be mixed with a fixer that is designed to be used with them. Hardener may not be used by itself or mixed with a fixer not designed for it. This information came from an APUG's resident chemistry expert when I asked a similar question.

I have a small bottle of Kodak Professional Fixer just for this type of situation. For everything else, I use Ilford's Rapid Fixer that manufacturer says NOT to be used with a hardener.

trexx said:

BUT often ammonium thiosulfate fixers are considered to be alkaline even though the pH is well under 7

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Now that is the most confusing thing I've read yet. Is this simply a nomenclature error?

Again, hardening is a feature I'd rarely want, since it's only required for some old-formula films. And I hear you're supposed to avoid it for paper if at all possible.

Any idea what the characteristics of Kodak Rapid fixer (two part liquid) are? I understand that one of the two is simply a hardener and is unnecessary.

Yup. The small bottle that comes with Kodak Rapid Fixer is a hardener.

Kodak regular fixer (powder type) lasts for at least 6 months, although the bag says 2 months. I keep a small bottle of it just for brown/sepia toned paper processing. With paper processing, especially Fiber paper, use of hardening fixer makes it more difficult to wash. I also read in various toner chemical instructions, hardening fixer can prevent toning.

Where are our resident chemistry experts? HELLO??

(Interesting, I thought that the regular ol' Kodak fixer was a hardening fixer... I guess I was wrong? I never did bother to try it, since rapid fixers were the only thing that were recommended, and I never liked mixing up powders. But that was before I discovered XTOL. Anyway...)

The regular Kodak Fixer (either powder or liquid) does have the hardener "built in". It is not a rapid fixer.

The Kodak Rapid Fixer is packaged (in the quantities most of us use) with two separate bottles. Solution "A" alone is a non-hardening Rapid Fixer. Solution "B" is hardener which one can either add or not.

Solution "B" is strongly acidic. It is the reason that Kodak Rapid Fixer attracts Hazmat charges when it is shipped.

If you buy Kodak Rapid Fixer in very large quantities solution "A" and "B" are sold separately, but you need either high volume machine processing or a group darkroom for the quantities to make sense.

Alkaline ammonium thiosulfate fixers tend to smell of ammonia, acidic fixers tend to smell of sulfur dioxide. Approximately neutral fixers smell less, which was a "design criterion" for my "rapidised normal fixer" OF-1.

Yes, the regular old Kodak fixer IS a hardening fixer.

I've used both "regular old Kodak fixer" and Ilford's rapid fixer. The former has the hardener and the latter does not. The only difference really is how fast the process completes. I haven't noticed any difference in the final products one way or the other. Are you trying to accomplish anything in particular?

Kodak fixer (the powder one with the hardener) does last quite a while. 6 months or longer is my experience and by them, I usually exhaust its rated capacity anyway.

I have been using Photographer's Formulary TF-5 fixer for some time now and I am extremely satisfied with it. By neutralizing the fixer, they made it practically odor free. It's also perfect for pyro development as it has no effect on the image stain.

An acid fixer is unstable and will evenually begin to precipitate elemental sulfur. To prevent this from happening all fixers contain sodium sulfite. The sulfite acts as a preservative in that it combines with sulfur as it forms to form thiosulfate. This protective action will continue until all the sulfite has been used up. At this point the fixer will begin to precipitate sulfur and it must be discarded.

To answer tkamiya, I'm trying to shop for alkaline fixers since I'm trying to eliminate an acid stop bath from my process. My theory is that my current process (alkaline developer, acidic stop, and who-knows fixer) is far more abusive on film than an all-alkaline process (alkaline developer, water stop, alkaline fixer). I've seen some spots on a few images, and I'm wondering if changing my development techniques will help. Also, I'd save all my stop bath for paper developing.

yeknom02 said:

My theory is that my current process (alkaline developer, acidic stop, and who-knows fixer) is far more abusive on film than an all-alkaline process (alkaline developer, water stop, alkaline fixer).

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AFAIK, there is no data to substantiate such an assertion. There have been long and lively threads on APUG about the gelatine iso-electric point, swelling at various pH's, etc. I have not seen anything conclusive.

There is always the problem of development not being quickly stopped in an alkaline system.

A simple solution of sodium thiosulfate and sodium sulfite provides a alkaline fixer.

The traditional fixer has existed for many MANY decades and used by many MANY photographers and labs successfully. If you are having problems with staining or spotting, the issue isn't likely be the fixer itself but rather, how it is being used. It could be caused by something else, too.

Good luck in finding the problem though.