Something's precipitating out of my Kodak Rapid Fix

When Kodak stopped producing the 5gal containers of Rapid Fix part A, I guess they dumped a bunch of them into the Australian market and I've been buying them from a local supplier until they ran out recently. I seem to recall that they stopped being available in NYC in 2019 so I guess they're about 6 years old now.

But I've just noticed that at least one of the bottles has begun to separate, with a yellow precipitate forming on the bottom and some crystals floating in the solution. Presumably it's ammonium thiosulfate separating, as it now has a pretty strong sulfur smell.

I've only got one bottle left so it's not that big of a deal, but does anyone know if I might be able to get it back into solution? It still clears film so I guess it's alright for now.

Yep, sulfur. I had an old bottle (to make 1 gallon) I tossed out a couple days back, from 2019. Unopened.

Sorry didn't answer your question. No re-dissolving.

It is a bit of a pain to try and use, it can be decanted/filtered still stinks.

Trey said:

Presumably it's ammonium thiosulfate separating, as it now has a pretty strong sulfur smell.

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As @mshchem explains above, it's not thiosulfate, it's actually sulfur. Especially in acid fixers, self-decomposition is a problem and it tends to accelerate. Your fixer is basically toast at this point. You could filter out the sulfur, do a strip test with the fixer and then continue to use it, and it'll likely work. But evidently it's recommended to just purchase some fresh fixer instead.


Here's some elemental sulfur I 'harvested' from a bottle of decomposing fixer part from a Fuji RA4 blix (for all color printers out there: do NOT buy CPRA blix; instead, stick with the monopart stuff!)

You can filter it and use it for anything that is short term and is likely to be discarded.
Otherwise, you will be risking sulfur getting embedded into the final product, which is terrible for longevity.

When your fixer starts to sulfur-out, it's getting progressively weaker... and fast! Plus, there are sulfur particles in it, which will adhere to the emulsion of anything you fix. Even if you filter it, some micro-particles will make it through.

Fixer is cheap. Unless you're really strapped for cash, toss it and buy new.

Doremus

It is elemental sulfur. If the fixer is unused, or used only for some times, sulfurization of fixer will lead to precipitation of elemental sulfur. But if this reaction happens in used fixer (or in blix in color paper process RA-4)., the product will be a black salt. silver sulfide (Ag2S), which will stain all the vessels and equipment. It is very ductile. almost like a metal, and is not soluble in water. It is actually the same compound that tarnishes silverware and jewelry. Kodak recommends using a household bleach (sodium hypochlorite solution), followed by standard photographic fixer for removing these stains,

koraks said:

Here's some elemental sulfur I 'harvested' from a bottle of decomposing fixer part from a Fuji RA4 blix (for all color printers out there: do NOT buy CPRA blix; instead, stick with the monopart stuff!)

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Haven´t seen any monopart blix by Fuji Hunt in the market for eons. All of the EnviroPrint blixes come now in two parts. EnviroPrint developers are mostly monopart, and they do keep well. Unfortunately, this can happen also in the fixer part of the EnviroPrint. I had my last one liter bottle of 215 AC sulfurized just about a month ago. I put it in smaller bottles more than a year ago, maybe two years and this last bottle of concentrate sulfurized about a week after opening it.

Samu said:

I put it in smaller bottles more than a year ago, maybe two years and this last bottle of concentrate sulfurized about a week after opening it.

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That's much better shelf life than I got from the CPRA that I got that sulfur from. That sulfured out within 6 months. Stored in entirely full, glass bottles.

Personally I'd probably just discard the bad fixer.

But... in certain circles it's fairly well known that as colloidal sulfur is formed it can quickly be converted, by the standard preservative, sulfite, back into thiosulfate.

In other words, "sulfuring out" does not happen when there is still "free sulfite" in the fixer solution. So, what to do when your "free sulfite" is gone? Just add some more; typically you might wanna add about 5 to 10 grams per liter of sodium sulfite to tide you over.

I'm kind'a doubtful that this will pick up the sulfur sludge. But it oughta restore the rest of the fixer, minus the lost thiosulfate (in the sludge) back to more or less normal function. I would suggest to decant off the clear liquid, then add the sodium sulfite to this. Have I actually done this myself? No, not exactly... in my photo lab experience I don't have much experience with fixer that is this far gone.

What is my actual experience? (Tech stuff coming... no need to read if you don't care.)

Well, I spent a number of years as the QC manager in a large lab, part of a studio chain outfit. This was not a fluff position. We did the conventional "process control," running about 40 to 50 control strips per day, troubleshooting all problems. Super tight control plots. Plus, we oversaw ALL of the chemical mixing; we ran the chemical analysis on chemicals to be regenerated, and made the mix sheets for the chemical operators who actually did the mixing. Afterwards we screened every mix, typically just a pH and sp gr, before it was cleared for use. (We kept the records as we also did periodic reports of actual film/paper usage vs chemical usage; also used for audits of the silver recovery.)

So... part of the RA-4 bleach-fix is actually an ammonium thiosulfate fixer, "preserved" by sodium sulfite. Just like I described above. Here's the regeneration procedure: blix overflow from all paper processors goes to a common collection tank which automatically pumps to a silver-recovery system. It's a special multistage "continuous" electrolytic system which can start and stop automatically, using preset flow rates and specific amperage settings on each of the "electrolytic cells." Blix goes in one end, silver laden, and comes out the other end with the majority of silver removed. (My department periodically measures the silver concentration in each cell, and occasionally modifies the flow rate and/or cell amp settings as needed.) But... a side effect is that the blix has been electrolytically "reduced," it must be heavily aerated to restore its "bleaching" power. So it (automatically) goes through a multi-stage (continuous) sparging system. (Anyone who understands this realizes that virtually all of the sulfite, the preservative, is oxidized to sulfate.) So the blix goes into temporary holding until the mix operator is ready to regenerate a batch. The mix operator will do so according to our mix sheets, starting with specific volume of the treated blix, then the specific chemicals needed (including sulfite) then top with water. This includes a "blanket" pH adjustment. A sample goes to our QC lab, who calls out a fine pH correction then gets a verification pH. The mix operator pumps it over to replenishment tanks, then is ready for another batch.

This is just a taste of the sort of thing we would do. Our C-41 fixer was also electrolytically desilvered. Actual operation is done by the mix operators, with final screening done by QC department. Fwiw I have personally done at least a handful of studies during the fixer desilvering. Periodically I would pull a fixer sample, noting the total amp hours. Then check pH and do the chemical analysis for both sulfite and thiosulfate, and silver. So I can plot these on a graph. I forgot to mention that, in electrolytic desilvering of fixer, sulfite is "consumed" at the anode as silver is plated on the cathode. (The rule of thumb is that for each gram of silver plated, roughly the same weight, as sodium sulfite, is "consumed." So you must start with comfortably more than that.) There's no real purpose to these tests, other as a curiosity sort of thing, just to see if our "understanding" is correct. Well, and to test the "current efficiency" of our system. As a note, we did once try regenerating C-41 fixer, just "to see." It doesn't work - C-41 film releases a certain amount of iodide ion, which sorta "poisons" the fixing operation (it is significantly slowed down). Actually it's possible to reuse some moderate proportion of the used fixer, depending on what replenishment rate (or "usage") you are putting on it. We considered it not worthwhile. Whatever savings there might be can likely be matched by using multi-stage fixing at a lower replenishment rate. Then do "terminal" desilvering at the end. Actually, if you do commercial processing in the US, and are working under the terms of a "stringent" sewer permit, it may be folly to try to conserve fixer. You might need multi-stage fixing (more than two) at a higher rate just to keep your wash water from exceeding the silver limit.

Sorry to get so wordy. But on the internet you don't really know who you're talking (or listening) to. So perhaps you can see that I have real-world experience with "sulfite in fixer."

Ps, it may sound like this is recent experience; to be clear my last (serious) experience with those things is probably something like 20 years back. So going from memory that is only getting more distant.

Mr Bill said:

So, what to do when your "free sulfite" is gone? Just add some more; typically you might wanna add about 5 to 10 grams per liter of sodium sulfite to tide you over.

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Yeah, which is what I've done, but it's only marginally effective and offers only a slight delay of the inevitable.
A more pressing concern is that sulfite is commonly and cheaply available as the sodium salt, and you ideally don't want to use that to recover a decaying rapid/ammonium fixer as it'll slow the fixer down considerably. The solution is to purchase ammonium sulfite, but in consumer/hobby quantities this likely is more expensive than just getting some new fixer.

Mr Bill said:

I'm kind'a doubtful that this will pick up the sulfur sludge.

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It won't. The fact that thiosulfate breaks down into sulfur is a good indication of which side of the equation the equilibrium leans to. I've not looked into it, but I expect that to form thiosulfate from sulfite and sulfur, energy would have to be added to the system. I.e. it's not going to happen at room temperature and normal pressure.

Mr Bill said:

So... part of the RA-4 bleach-fix is actually an ammonium thiosulfate fixer, "preserved" by sodium sulfite.

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No, commercial RA4 blix formulas generally do not contain sodium ions. At least not in significant quantities; there may be traces present, but the sulfite is generally added as the ammonium salt.
I don't think commercial blix reconditioning systems rely on sodium sulfite for the simple reason that it would ultimately result in the entire blix being essentially based on sodium thiosulfate, which would be far too slow to get the job done at RA4 process conditions.

koraks said:

No, commercial RA4 blix formulas generally do not contain sodium ions. At least not in significant quantities; there may be traces present, but the sulfite is generally added as the ammonium salt.

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Well, I can't argue about that, regarding CURRENT blix, especially the more modern rapid access style. Because1) I don't know for sure, and 2) it seems sensible that a chemical manufacturer could easily avoid the sodium aspect.

And... they could also do the same in blix regenerator packages. And by "regenerator" I specifically mean such that would be added to the collected process overflow which has been desilvered and aerated, and needs both the bleaching and fixing agents brought back up to chemical specs.

koraks said:

I don't think commercial blix reconditioning systems rely on sodium sulfite for the simple reason that it would ultimately result in the entire blix being essentially based on sodium thiosulfate, which would be far too slow to get the job done at RA4 process conditions.

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This part, "for the simple reason..." I do NOT agree with. Except for possibly the case of a "rapid access" blix, with very short immersion times.

The more conventional systems, following the standard times in Kodak's Z manual, DO NOT have any problem with adequate bleach-fixing, when made with SODIUM sulfite. Specifically when used in commercial processing machines equipped with squeegees at each tank exit, and where the paper goes directly from developer into the blix. Additionally, no process problems exist when such blix is custom regenerated (via bulk chemicals) using SODIUM sulfite. In such cases the "reuse" is generally limited to about 85%, meaning that, say, an 800 gallon final mix would start with about 680 gallons of process overflow. If one tries to increase the reuse ratio beyond that, then yes, this would likely cause a problem.

To repeat, first-hand experience, albeit older, has shown no problems in "standard" commercial machine processing when using sodium ion (specifically sodium sulfite) in the blix.

Now, something I'm gonna be a bit vague about, but which HAS been mentioned on the internet is that various manufacturing companies H AVE, for various reasons, licensed various photofinishers to use the confidential formulary manuals of such manufacturers.

I'm gonna expand on the sodium ion thing in a following post...

koraks said:

A more pressing concern is that sulfite is commonly and cheaply available as the sodium salt, and you ideally don't want to use that to recover a decaying rapid/ammonium fixer as it'll slow the fixer down considerably. The solution is to purchase ammonium sulfite, but in consumer/hobby quantities this likely is more expensive than just getting some new fixer.

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In the realm of film fixers (prev post was mostly RA-4 PAPER process) I don't see the use of the sodium sulfite in the fixer as much of a problem. There is a relatively minor amount compared to, for example, the amount of sodium that would be used in a non-rapid style sodium thiosulfate fixer.

As an example see Kodak's H24 Motion picture manual. (Should be available on the internet.) In module 07, page 7-33, a formula is given for fixer. In a "fresh tank" the formula is, roughly, ammonium thiosulfate (58% solution) = 185 mL/L, then two forms of sulfite ion. They are: sodium sulfite = 10 g/L, and sodium metabisulfite = 8.4 g/L.

So the preservatives are both using sodium, whereas the fixing agent is ammonium thiosulfate. I went through and estimated the relative amount of sodium in the preservative package, compared to how much sodium would come into play if SODIUM thiosulfate (slow fixer) had been used.

For the Kodak ECN fixer I estimate that the 10 grams sodium sulfite divided by the molecular weight of 126 grams =~ 0.08 moles. But... since each molecule contains TWO sodium atoms this gives 2 x 0.08 = 0.16 moles of sodium per liter. In a similar manner the sodium bisulfite gives a further 0.09 moles of sodium, for a total around 0.25 moles sodium in the ECN fixer. Now the question is, how significant is that, compared to if the fixing agent = SODIUM thiosulfate?

I estimate the ammonium thiosulfate used to be very close to 1 mole per liter. So a straight up change to SODIUM thiosulfate, with TWO sodiums per molecule, would have close to 2 moles of sodium. This is compared to only 0.25 moles sodium coming from the preservatives (sulfite). In other words the use of sodium sulfite in a rapid fixer (ammonium thiosulfate based) is only about 1/8 the sodium content if the fixer had been based on sodium thiosulfate. So it seems silly to say that adding more sodium sulfite to the rapid fixer is gonna bring it down to the level of an old style sodium thiosulfate fixer.

I don't know how clear this is to the "typical" reader who might be following this,, so let me just repeat that the Kodak motion picture manuals, which would be used by any lab mixing their chemicals from components, do not seem to have a problem using sodium sulfite, ie, adding sodium ion, to their rapid fixers.

So I personally do not see much problem putting more sodium ion, in the form of sodium sulfite, into a rapid fixer as a means of saving it from a collapse of the thiosulfate (sulfuring out). From a gut feeling I have the sense that simply using a fixer, where the silver concentration is increasing, would have a larger effect on the fixing speed than a moderate amount of sodium ion added. But... I have never specifically tested for this. My experience has been primarily based on following the specifications of the manufacturer with respect to time and temperature, etc., and to confirm that the chemical functions are comfortably completed within that time window. And... we made sure that the chemicals remained within "normal" analytical specs. So again, I've never actually "saved" a fixer during a "sulfuring out" failure cuz we never allowed the fixer to get that far.

koraks said:

Yeah, which is what I've done [adding sulfite to a fixer which has started to sulfurize], but it's only marginally effective and offers only a slight delay of the inevitable.

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All I can say is that this is contrary to what I think I know. My guess would be that you didn't add enough. Perhaps the sulfuring out was so advanced that the additional sulfite was not enough. Or that perhaps, for some reason, the solution pH had gotten too low. I would guess, that had a sulfite analysis been done, that it would have been back down to zilch again.

To me it would've been a fun thing to investigate back in the day. I have little doubt that we would have gotten to the bottom of it. Perhaps not us directly - I don't understand the deep down chemistry - but Kodak would have connected us with their knowledgeable people, or perhaps some other alternative source. But those days are long gone.

I'm still gonna believe more sulfite would have stopped the collapse of the thiosulfate unless I hear of 2 or 3 more people who tried and failed. Then the issue will sit in the back burner of my mind until... who knows?

Mr Bill said:

All I can say is that this is contrary to what I think I know. My guess would be that you didn't add enough.

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I know for sure I added more than enough (significantly more than what you indicated) and that it definitely didn't help much in the long run. It stalled things for a few weeks.

As to the sodium in blix: my concerns probably derive from the repeated warnings of PE against sodium in film blixes. Paper is a different animal. IDK what the present technical bulletins from Fuji say about blix regeneration and whether it's OK to use sodium ions in such a process. I doubt it, certainly because of the fact that virtually all blixes now are rapid access, and some papers (esp. Fuji Maxima) require every bit of blixing they can reasonably get in a commercial process since they blix out significantly slower than other papers. For amateur/hobby uses, it's usually feasible to extend blix times to introduce a safety margin, in which case it's probably a moot point whether or not there's some sodium in there.

Mr Bill said:

I'm still gonna believe more sulfite would have stopped the collapse of the thiosulfate unless I hear of 2 or 3 more people who tried and failed.

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We're talking heaping tablespoons per liter here, Bill. About as much as I could get to dissolve in the concentrate to begin with. That didn't do the trick. There's nothing more you can do at that point.

koraks said:

We're talking heaping tablespoons per liter here, Bill. About as much as I could get to dissolve in the concentrate to begin with. That didn't do the trick. There's nothing more you can do at that point.

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Ahhh... ok, I take your point. I presumed you were talking about quantities similar to what I had originally said. Not "as much as can be dissolved."

Also, I see that you are talking about the concentrate. Whereas I've been in reference to working concentrations. I can certainly understand that the concentrate may be at the solubility limits, and that perhaps special tricks are needed to even get there. I

I've been sorta presuming that all of us are talking about mixing the concentrate into something akin to a working solution.

koraks said:

As to the sodium in blix: my concerns probably derive from the repeated warnings of PE against sodium in film blixes.

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Yeah, I would never wanna deal with a FILM blix on any serious basis. Re: PE, he was a huge asset to Photrio (and previously to Photo.net). It seems that most people who have been deep inside the manufacturer's bowels retire and disengage from the business. Yet he kept on, always ready to share his knowledge with the enthusiasts.

But from our business standpoint, as users of these systems, we always had better sources. I recall PE had mentioned that, in his group, they would "invent" and trial things, but when it was time to roll out and monetize their research, it was handed off to a group called "Photo Tech," I believe, who would design it into replenishment systems and/or make it "package able" for customers. This would be the sort of information source more directly useful for us. In my later years I was privileged to be able to sit in on occasional so-called technology reviews, where new research developments would be revealed, with the idea that we might be able to see some potential applications that they did not. Several times I've spent the better part of a day with someone from the Research Labs, once a color scientist, for example, on some sort of equipment/application being trialed. Ok, I'm just bragging now, but this sort of thing was beyond my wildest dreams as a kid intending to be a "photographer." (Ps, he explained to me why, conceptually, an inkjet print would generally be more susceptible to visual "color shifts" than an RA-4 print when viewed under spectrally deficient lighting.)

Mr Bill said:

It seems that most people who have been deep inside the manufacturer's bowels retire and disengage from the business.

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For the most part, yes. The ones I've spoken to tend to not post on forums. I don't think they have the kind of passion/interest in the subject matter to spend their free time on it.

Mr Bill said:

(Ps, he explained to me why, conceptually, an inkjet print would generally be more susceptible to visual "color shifts" than an RA-4 print when viewed under spectrally deficient lighting.)

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I doubt that's a hard & fast rule given the various options for inkjet dyes and particularly pigments, and pigment dispersions. It mostly depends on the spectral profile of the colorants involved. I would be hesitant to generalize them in a single stride and regard them as static. The variety and rate of change are insanely larger than the relatively static and small universe of RA4 dyes.

Trey said:

When Kodak stopped producing the 5gal containers of Rapid Fix part A, I guess they dumped a bunch of them into the Australian market and I've been buying them from a local supplier until they ran out recently. I seem to recall that they stopped being available in NYC in 2019 so I guess they're about 6 years old now.

......

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I noticed that for sale in Melbourne, and was tempted, but I didn't get around to buying it.
Now that C-41 fixers are not as inexpensive as they were, I just buy Ilford fixer which is moderately acidic. I add some ammonia solution (sometimes called ammonium hydroxide) to lift the pH a bit, and it lasts forever, like the old Agfa FX-Universal, pH=7 (I still have an unopened 5L of that which hasn't precipitated, and it must be 15 years old by now)

I had never heard of adding sulfite to acid fixer to preserve it (as mentioned above), and it makes sense, but apparently it's hard to get it to dissolve in the concentrate.

Shake it up real good and dilute it for fertilizer. As long as it hasn't had film or paper fixed in it.

koraks said:

It mostly depends on the spectral profile of the colorants involved.

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Yes, exactly. With the general rule that something capable of more saturated colors will also have "peakier" spectral absorbance curves. And is therefore more susceptible to a visual mismatch with a spectrally deficient lighting source. So the only workaround I see, for high saturated color capability is to have more colorants such that a spectrally deficient light source can't easily aggravate the dye peak(s) interaction with human color vision.

FWIW going back to 12 or 15 years ago I had probably seen every major dye sub or inkjet printer suitable for high volume and 8x10" and larger print capability. (Vendors would bring em in cuz of the potential sales.) Now, we only looked at manufacturer supported ink sets, not 3rd party, so limited there. (We had a 100% satisfaction guarantee. Not that we could force them to be satisfied, but to refund money. So no 3rd party risks.) But when we got halfway serious about something I would borrow 3 or 4 people from a production area to do a series of paired-comparison tests using an abbreviated color ringaround under a handful of lighting conditions. The idea being that if you changed your preferred print(s) under different light sources, then this is not a good thing. In every case I tried the RA-4 prints were more stable. With the others there were sometimes startling visual changes under something like an energy efficient fluorescent lamp.

I also used color profile-making software to examine the color gamut under various simulated lighting (I'm already making the color profile to make sure they're good.) But the human tests were the real clinchers, to me.

I would say, to keep up with the current advances, attending the IS&T color conferences, or whatever they have today, is perhaps the best way. Historically it has been, anyway.

I should apologize for running off topic. So I do. I apologize.

john_s said:

I had never heard of adding sulfite to acid fixer to preserve it (as mentioned above), and it makes sense, but apparently it's hard to get it to dissolve in the concentrate

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Hi, yeah, well if you look at thiosulfate fixer formulas they all have it. So if not as a preservative, the question would be, why? Actually it's pretty necessary for electrolytic silver recovery. If you look at fixers specifically designed for that, with names like "electro-silver" or the like, they most likely have higher levels of sulfite.

Ps, I have never attempted to modify the concentrates; only the processing solutions for regeneration, etc. But with paper blix, we essentially used it forever. Not exactly true, though, cuz there is always some surplus that gets discarded. So it is slowly being replaced.

Thanks for the on- and off-topic replies everyone. I'd forgotten how much I miss discussion forums.

This is for a small community darkroom (sydneydarkroom.com), so we do try to be as frugal as possible. Since this fixer could just be used for first time darkroom students and workshop attendees who probably won't keep their prints anyway, I might try to rescue some of the fixer. Otherwise I've already ordered some fresh.

john_s said:

I noticed that for sale in Melbourne, and was tempted, but I didn't get around to buying it.
Now that C-41 fixers are not as inexpensive as they were, I just buy Ilford fixer which is moderately acidic. I add some ammonia solution (sometimes called ammonium hydroxide) to lift the pH a bit, and it lasts forever, like the old Agfa FX-Universal, pH=7 (I still have an unopened 5L of that which hasn't precipitated, and it must be 15 years old by now)

I had never heard of adding sulfite to acid fixer to preserve it (as mentioned above), and it makes sense, but apparently it's hard to get it to dissolve in the concentrate.

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Where have you been getting yours? Vanbar seems to have the best prices from what I've seen.

Mr Bill said:

Hi, yeah, well if you look at thiosulfate fixer formulas they all have it. So if not as a preservative, the question would be, why?

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Not only as a preservative but also to "prevent discoloration of the fixing solution by reacting with the oxidized forms of the developing agents that might be present."

Haist Volume 1, Chapter: The Fixing Process, page #571-576.

Trey said:

This is for a small community darkroom (sydneydarkroom.com), so we do try to be as frugal as possible. Since this fixer could just be used for first time darkroom students and workshop attendees who probably won't keep their prints anyway, I might try to rescue some of the fixer. Otherwise I've already ordered some fresh.

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Hm, well, there's two things that come to mind:

1: Yes, I understand and by all means go ahead. The main challenge is that with 'broken' fixer like this, you ideally want to have an idea after salvaging it how effective it still is. You can no longer rely on the manufacturer's recommendations w.r.t. capacity and fixing time. You could compare the clearing time of this salvaged fixer to fresh/good fixer using a strip of film (paper of course doesn't work as you can't really see it clear) and then guesstimate a factor to correct the fixing time with. Let's say fresh fixer clears a strip of film on 30 seconds and your salvaged fixer does the job in 45 seconds, you could just have students fix their prints for 50% longer than they originally would. For capacity I don't know if there's any good way to estimate it in this scenario, so all bets are off.

2: At the same time, what you're trying to do (I suppose) is teaching students how to do things right and you want to keep them motivated at the same time. I imagine that things like "ah, this fixer is broken so we all need to fix 50% longer" will raise some eyebrows and potentially confuse students unnecessarily. It also shows that you perhaps don't trust them with fresh chemistry or don't value them to the extent of allowing them the use of fresh chemistry. Finally, if a few prints end up underfixed and they develop brown spots in the student's hands, I suppose that won't do much for motivation either.

Keep in mind that for all your labor and the risk of something happening to students' prints (and motivation), you're saving, idk, $25 worth of fixer. Is that worth it?
Personally, I'd bring that problematic fixer home and use it up myself.

The chemical equilibrium is influenced by temperature, pH, and concentration. When sulfur is added to a saturated sodium sulfite solution and boiled, the reaction can be driven towards sodium thiosulfate, achieving a yield of ~90% in industry. This can result in an effective fixing solution. But for individuals (not large labs with 'regeneration' methods or factory), it might be more convenient to buy some new sodium thiosulfate(for pools, if you can find wholesale, $25 can buy dozens of pounds, some times it can be cheaper.....) and mix some new fixer, slower but "right". It might also be good to fun to provide students with a safe solution-mixing experience at begining.

Yezishu said:

When sulfur is added to a saturated sodium sulfite solution and boiled, the reaction can be driven towards sodium thiosulfate

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I might try that, just for fun. Yield will likely be pretty horrible, but it'll be a fun experiment to see if it can be used to yield a working fixer.