A Neutral Quick Fixer Formula

[halfaman]

• Choice of C-41 fix. I found the best price is Champion Mydoneg; a distributor sell it for 30€ plus hipping for 5L concentrate. Is Champion still a reputable brand?
  
  

  CHAMPION - Fixateur C41-RA Mydoneg Universal pour faire 2x5L à 2x15L - CHIMIE Couleur/Développeuse C41 - PH Distrib.com

  CHAMPION - Fixateur C41-RA Mydoneg Universal pour faire 2x5L à 2x15L de Champion est vendu sur la boutique PH Distrib.com dans la catégorie Développeuse C41

  www.phdistrib.com

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This is the fixer I am using actually in C41 with no problems so far.

 

[Kino]

In order to get the ingredients dissolved with the least amount of time, I recommend the following procedure:

1. Fill a container with about 60% of intended fixer volume with hot tap water (50-60°C/120-140°F).
2. Add the calculated amount of Sodium Thiosulfate
3. Stir vigorously. The Sodium Thiosulfate will cool down the water substantially while it dissolves. If you do not start with very hot water, the solution will get close to freezing point and dissolution will be extremely slow.
4. After the Sodium Thiosulfate has been dissolved, add the Ammonium Chloride. This will cool down the solution yet more. If the volume is still below the intended final volume, add hot water to reach it. Chances are, that the solution will reach roughly room temperature.
5. Add the Sodium Sulfite and the Sodium Metabisulfate at once and dissolve it. You should now have an ever so slightly milky solution, which should be mostly odorless.

Maybe this should be added to the resource page?

 

[koraks]

Maybe this should be added to the resource page?

Yes, good idea. I've edited it in.

 

[Rudeofus]

Questions to the knowledgeable ones, after doing a little homework.

• pH. Fixers for C-41 are specified having a pH 7.5...7.8, while rapid fixers for B&W are specified pH 5.0...5.5. What are the trade-offs? Acid fixer, that I used so far, allows me (after a brief dip in acid stop) to turn the lights on as soon as the test strip is in the fixer. Neutral fixer will require a longer (30s??) stay in the stop bath. OTOH, neutral fixer is expected to be odorless. Any other trade-offs that i should know of?

What you think is "fixers for C-41" usually turns out to be "replenisher concentrate for C-41 fixer". Since speed is king in commercial C-41 processing, these machines typically go directly from acidic bleach (well buffered at pH 4.2-5) to fixer, carrying over quite a bit of acidity, therefore the replenisher has to be a bit on the alkaline side to keep the tank at target pH 6.5.

If you mix fixer just from this "fixer replenisher concentrate", your fixer will be at the pH both @koraks and you reported. The fixer itself will work just as well at pH 7.5, but Ammonia smell isn't all that great in open tray processing. There is absolutely no point in buying fixer starter for B&W processing, just add a few dashes of something acidic until the Ammonia smell is gone.

• Durability. C-41 fixer is generally sold in a pack of 5L concentrate. I'm a relatively low volume user. How long will the stock fixer keep before it sulfurs out?

It will not sulfur out. Unlike its acidic peers it will not leak out Sulfur Dioxide, its pH will not go down over time. You can measure its life span in multiple years, and even if you throw half of it away it will be cheaper than typical B&W rapid fixers. If you are a really low volume user, there are are neutral fixers marketed for B&W, and they typically come in 1 liter bottles.


Regarding speed of action: don't get hung up on fixer speed, look for washing speed, that's where you can save time and water. PE was enthusiastic for neutral fixers mostly for their washing speed.

 

[bernard_L]

@koraks @halfaman @Rudeofus thank you for your input.
Esp. this :

these machines typically go directly from acidic bleach (well buffered at pH 4.2-5) to fixer, carrying over quite a bit of acidity, therefore the replenisher has to be a bit on the alkaline side to keep the tank at target pH 6.5.
(...)
just add a few dashes of something acidic until the Ammonia smell is gone.

that explains the reason for the pH value in C-41 fixer

 

[koraks]

Yes, although I use C41 fixer replenisher without any acid added to it, but my film and paper processing all involve stop bath (or in the case of color negative, acid bleach) steps, so there'll always be a little carryover inherent to the process. Even without it, the fixer will work just fine if you don't acidify it.

 

[bernard_L]

A follow-up on my post #19 above. Having 2 and 1/2 bottles (500ml) of Fomafix from a purchase last year, I need to use them before I switch to C-41 fixer. With just pH paper at hand, I used ammonia to neutralize the Fomafix. Starting with 166cc of stock fixer --the amount to make 1 litre at Foma's recommended dilution 1+5-- I added ammonia until the pH paper read "7" (give or take). This happened after i had added 33cc of 22° Baumé (reportedly 11 Mol/litre).

The resulting neutral fixer had no smell --at least far less than the original one. And it cleared a negative clip at least as fast as the non-modified fixer.

So success and thank you to members who provided explanations about the pH of various kinds of fast fixer.

 

[Spektrum]

Dear Rudeofus, I have a question about the order of dissolving the ingredients. Your formula does contain sodium sulfite as a preservative and antioxidant, but also as a buffer.

I wonder if it would not be more appropriate to add sodium sulfite as the first ingredient to the solution.

Why?

1. Sodium thiosulfate oxidizes quickly and its fixing power decreases. Water contains large amounts of oxygen and if we dissolve sodium thiosulfate as the first ingredient, the oxygen from the water binds with sodium thiosulfate.

If we add an antioxidant to the water as the first ingredient, then this antioxidant will consume the oxygen from the water, stabilizing the environment and protecting sodium thiosulfate from oxidation.

2. In chemical practice (laboratory and photographic), the rule is often used:

"First the stabilizing component of the environment, then the active reagent"
- to achieve the correct pH,
- to prevent decomposition,
- to avoid undesirable side reactions.

This certainly works in the case of fixers based on sodium thiosulfate with the addition of sodium sulfite as an alkalizing buffer and antioxidant. However, everywhere in recipes I see sodium thiosulfate always as the first on the list, i.e. the first in the order to be dissolved.

3. Sodium thiosulfate, when dissolved in water, cools the solution strongly. Often the temperature of the solution drops dramatically and makes it difficult to dissolve the subsequent components (especially if we dissolve in cold water). Therefore, it is better to dissolve the "smaller" components first, which require less mixing, and then add sodium thiosulfate in batches.

Do I understand correctly? Forgive me, I don't have much experience, but I read a lot and then experiment with chemistry.

Kind regards,
Marcin

 

[Rudeofus]

1. Sodium thiosulfate oxidizes quickly and its fixing power decreases. Water contains large amounts of oxygen and if we dissolve sodium thiosulfate as the first ingredient, the oxygen from the water binds with sodium thiosulfate.

If we look at this chart here, we can estimate far less than 10 mg/l Oxygen in water. Comparing this to the 200 g/l Sodium Thiosulfate, even when accounting for the far higher molar weight of hype, shows clearly, that this little Oxygen really doesn't matter at all.

3. Sodium thiosulfate, when dissolved in water, cools the solution strongly. Often the temperature of the solution drops dramatically and makes it difficult to dissolve the subsequent components (especially if we dissolve in cold water). Therefore, it is better to dissolve the "smaller" components first, which require less mixing, and then add sodium thiosulfate in batches.

You want to start with the absolutely hottest water you can reasonably start with, which is typically 50°C from a hot water faucet. You do not want it to cool down while you dissolve the Sodium Sulfite. I have never had issues dissolving the other ingredients, but the Sodium Thiosulfate did take its time.

Your input from lab experience is well appreciated here, but in this specific case established practice is, as far as I can tell, the fastest way to get all this stuff dissolved.

 

[Spektrum]

Thank you very much for your answer. I am 52 years old. Sometimes I rely on old principles of photographic chemistry from the 80s. I remember that sodium sulfite was always to be dissolved as the first ingredient. The exception were developers containing methol, which was very resistant to dissolving in sulfite.

But by pointing to this chart you cleared up my doubts. Thanks again.