Converting C-41/E-6 BLIX into Separate Bleach and Fixer

[Photo Engineer]

Do not substitute Potassium Bromide for Ammonium Bromide.

As for Ferric PDTA, it is bright green at the working pH and not red like Ferric EDTA. It is strong enough to shorten the life of hypo when the two are mixed.

PE

 

[Paul Verizzo]

I suspected as much, really, for chemistry reasons, and not just bad luck. Thanks!

 

[Rudeofus]

Potassium Bromide should also work.

About BLIX temperature: I could imagine, that BLIX decay is more rapid at 45°C. If too much Ferric ion oxidizes Thiosulfate, you get weaker bleaching with Fe+++ ---> Fe++ conversion, and at the same time Thiosulfate oxidation to Sulfate causes both weaker fixation and slower diffusion. BLIX decay is massive when it happens.

 

[Photo Engineer]

Potassium ion has 2 bad effects. It may slow fixation rates and it will slow bleach and fix rates by comparison to Ammonium ion because Ammonium ion enhances fixing rates.

PE

 

[Paul Verizzo]

Thanks for the reasoning, PE.

But if I don't care about time - hey, I have more of that than money! - it would work?

How much?

Do I remember somewhere up-thread that additional bromide seriously extends bleach life? Or, just another random creation of old(ish) age?

 

[Rudeofus]

Potassium ion has 2 bad effects. It may slow fixation rates and it will slow bleach and fix rates by comparison to Ammonium ion because Ammonium ion enhances fixing rates.

This only applies to BLIX and fixer. It's a non-issue if a proper wash is done after bleach.

How much?

In case this question refers to required amount of Potassium Bromide: about 50 g/l would be good.

 

[Photo Engineer]

Ammonium ion also enhances bleaching rates by means of grain scrubbing. The Silver metal has adsorbed species removed by the Ammonium ion's solvent effect.

PE

 

[AgX]

The Rollei MSDS here is written up by Calbe Chemie, appears to be a German firm.

Calbe is not just a german firm.
It is the successor of what once was Orwo's plant for making processing compunds.

 

[Paul Verizzo]

Calbe is not just a german firm.
It is the successor of what once was Orwo's plant for making processing compunds.

I said German because of the "de" in the URL. And Orwo was East German, no? I miss the days when Orwo flooded America with inexpensive film. Not real good, but a bargain to just have fun with.

 

[Rudeofus]

Ammonium ion also enhances bleaching rates by means of grain scrubbing. The Silver metal has adsorbed species removed by the Ammonium ion's solvent effect.

There's plenty of NH4+ around in a bleach made from Ammonium Ferric EDTA and Potassium Bromide. Fuji wrote some patents, that a fixer made from 50% Sodium Thiosulfate and 50% Ammonium Thiosulfate is just as fast as one made from only Ammonium Thiosulfate. Therefore I would expect a bleach made with KBr to be in the same ball park as one made with NH4Br.

The biggest question is the exact composition of BLIX part A (or whatever part contains the bleach agent). If this part does not contain a bleach accelerator, then the bleach will be painfully slow, regardless of whether NH4Br or KBr are used. Since MSDS often don't list all components, it's a guessing game no matter what. The good thing is, that a failed bleach&fix cycle can be corrected post fact, so nobody really risks much.

 

[Photo Engineer]

I cannot confirm the facts we are discussing, but I can rely on experience. Small amounts of K or Na will do no harm, but larger amounts can slow any fix, bleach or blix down. K or Na have no effect on developers, of course, but Ammonium ion really messes with development. Chemistry is quite strange.

PE

 

[Rudeofus]

Small amounts of K or Na will do no harm, but larger amounts can slow any fix, bleach or blix down.

It is well known, that sodium and potassium will kill a Thiosulfate based fixer that's already rich in silver, with potassium causing damage earlier than sodium. But fresh Sodium Thiosulfate fixer will actually become faster with addition of potassium! The reason for the slowdown of used fixer with sodium/potassium is formation of insoluble mixed salts between sodium/potassium, silver, halide and thiosulfate.

There is no such effect with bleach, in fact Potassium Ferricyanide works just fine. There are Kodak color processes with a wash between bleach and fix, such as ECN-2 and ECP-2, and sure enough there are recommended bleaches which are loaded with potassium. BTW these are bleaches based on Ammonium Ferric PDTA. The likely reason, why some of Kodak's bleaches are ammonium only, is carryover,some Kodak processes don't require a wash cycle between bleach and wash.

 

[Photo Engineer]

I am aware that Ferri bleaches and others like that are so active that they are not slowed down. I don't have and never had extensive data on slow chelated iron bleaches or blixes related to ions other than that related to slowdown. I do know that K can slow down a chelated bleach or blix quite a bit of Ammonium. We tested quite a few combinations to get high speed when using chelated iron. Some of those tests were not in our patent on fast chelated blixes. All I can do is suggest that Ammonium Bromide be used, and if you wish to do a test comparison, I will be most eager to see the results.

PE

 

[Rudeofus]

I do know that K can slow down a chelated bleach or blix quite a bit of Ammonium.

Does this mean, that a bleach entirely with potassium and no ammonium will be slow, or that a bleach with ammonium and some potassium will be slow? I am ready to believe the first, but have difficulties believing the second.

 

[Photo Engineer]

That was a typo.

It should read "I do know that K can slow down a chelated bleach or blix quite a bit compared to Ammonium. It should be quite evident in chelated bleaches or blixes.

Sorry about that typo.

PE

 

[Rudeofus]

So a bleach with no ammonium ion would be slow, but a bleach with 50% ammonium and 50% potassium would be ok. Correct?

 

[Photo Engineer]

I believe so, but have never run that experiment. Therefore, I prefer to err (if I am erring) on the safe side.

PE

 

[sillo]

I'm looking to convert my Arista Blix into bleach. The original post mentioned being able to use Potassium, Sodium or Ammonium Bromide for this, but then these last couple of posts cast some doubt on that. The Potassium Bromide is significantly cheaper than the other two options so I was leaning towards that route. Is this still recommended and should this still yield results on par with a legitimate, purpose built bleach?

Also just want to add thanks for all the info contributed in here. I've been lurking for while and have learned so much.

 

[halfaman]

For me only ammonium bromide worked to do a RA-4 bleach from Blix. Potassium bromide was so slow that it was useless, no significant bleaching action after 2 minutes.

 

[Rudeofus]

There is a great chance, that Ammonium Bromide gives better bleach speed. The extra bleach speed may or may not be worth the effort obtaining it and the higher cost. If bleaching is done to completion, then results should be identical.

 

[sillo]

Thank you! Using the Potassium Bromide would typical bleach times still be around 7-8 minutes?

 

[Pixophrenic]

I am aware, Rudeofus, that this may come as a fly in the ointment for this long running thread, but it is sort of getting omitted that if you are to use bleach after color developer, there should be a serious wash in between. The combination used in C41 kits like Unicolor where film is plunged directly from color developer into blix is only possible when there is a thiosulfate present, which effectively inactivates traces of color developer carried over in film emulsion. Even if there is an acid stop, it is not enough to remove all of those traces. If those traces react with a bleach component that is an oxidizer, a heavy color fog results. So, a blix was a somewhat elegant solution for this problem. Previously, other processing sequences included an intermediate acid fixer after color developer, then a wash and then a ferricyanide bleach. A Fuji E6 included a separate pre-bleach, with the purpose of destroying the color developer traces. Consequently, your goal of avoiding an incomplete bleach-fixing could be facilitated by using a stop-fixing step (half-strength common acid fixer) directly after color developer, followed by a brief wash and then the blix, included in a kit. IMO, the standard solution offered by Unicolor kits (developer-blix, no wash in between) is a valid one, as long as one does not get too greedy.

 

[Rudeofus]

E6 indeed uses a prebleach, but the official C-41 process goes directly from color developer into bleach. BTW there were several reports here, that going from C-41 CD directly into used BLIX also causes yellow splotches in the final image, especially with 120 type roll film.

Here are my conclusions: you can go directly (means: with little washing in between) from color developer into bleach, if and only if the bleach is reasonably acidic, which means pH at or below 5. If your bleach is more neutral, you should make sure, that there is at least a thorough wash or a clearing bath between color developer and bleach.

Ron Mowrey once recommended a clearing bath (1% Sodium Sulfite in water) to be used before strong bleaches. If you do C-41, I would recommend 1% Sodium Metabisulfite as a combined stop/clearing bath. Obviously these clearing bathes also work with bleaches based on Ammonium Ferric EDTA.

 

[Pixophrenic]

You are right, and consequently an acidic fixing (doubling as a stop bath) used to be a staple of colorneg process. I think Mason explains in detail that both acidic pH and thiosulfate effectively prevent the color fog. I also wanted to add that in fact different color film brands may react differently to the two-bath procedure, while being C41 compliant. PE said that sometimes he used an acid-sulfite.bath after the color developer. The word "sometimes" always worried me, but unfortunately I can no longer ask the author of its exact meaning. I only could infer that some films may benefit from it, and some others may not.
Examining the ECN-2 process, I also found that Kodak suggested several different bleaches, and surprisingly one of these is the good old ferricyanide-bromide. So a switch from that to ferric EDTA one may have been dictated by a political reason rather then chemical. You would understand that while PE was alive, mentioning this could have been awkward, him being an author of the respective patent.

 

[halfaman]

As far as I know a stop bath is mandatory before ferricianyde bleach (any trace of active CD produces stains) and reccomended with modern color bleaches if they are going to be reused to preserve acidic pH.