Alternative bleaches for homebrew color film processing?

[Donald Qualls]

When my darkroom was last set up, I had processed a few rolls of C-41 film in homebrewed Dignan two-bath C-41 developer, using Kodak Flexicolor bleach/fix and stabilizer; the results were encouraging (I did it this way because "kits" were too expensive for the amount of film I'd process during their storage life, and Flexicolor developer used a starter/replenisher system that depended heavily on high volume processing).

Now it seems it's gotten hard to get even the blix and stabilizer for Flexicolor online, chemistry kit prices seem even higher, and I'm looking at alternatives to finish homebrewing the process, for both C-41/CN-2 negative films and E-6 chromes.

For chromes, I'll need to mix a single-bath color developer, since two-bath depends on dry film to soak up the Bath A -- or else I'll have to dry the film between first dev and color dev (light fogging is one thing, but hanging the film for a couple hours at that stage might result in enough overexposure to go over the peak of the curve and make the halide lose density). That doesn't seem difficult; there are formulae online and I don't recall them requiring any exotic chemicals; CD-4 was readily available last time I checked and it seems Formulary and another chemical provider still have it.

However, the other step is the harder one -- bleaching. Common fixers work fine on color film stocks (I'd likely end up using two-bath fixing with plain hypo, because it's easy and cheap), but one needs to either remove or rehalogenate the silver first, or wind up with a "bleach bypass" look in negatives and extreme overall density in chromes.

"Correct" color process bleaches for C-41 and E-6 use an iron EDTA which is fairly hard to come by, but there are multiple other methods I know to bleach developed silver: potassium dichromate in sulfuric acid, hydrogen peroxide in citric or acetic acid (or as a two-bath, multi-pass process), potassium ferricyanide with a halogen donor such as potassium bromide, or iodine and potassium iodide. The first two directly remove the developed silver, the latter pair rehalogenate for later or simultaneous fixing. Iodine/potassium iodide is problematic because silver iodide is relatively difficult to fix away, so I don't seriously consider that bleach system. Potassium dichromate is toxic, carcinogenic, and handling the acid is a safety concern (not to mention availability of sulfuric acid in these times).

That leaves two processing I've never attempted (on color film).

Hydrogen peroxide is apparently fairly commonly used to bleach between developers in B&W reversal; with the acid catalyst, it dissolves the silver, which then precipitates in the solution in a form that can redeposit on the film or paper, causing yellow/brown silver staining (which I've seen in video of reversing in-camera paper negatives for direct positive). This can seemingly be avoided by ensuring the emulsion isn't up in the bleach solution. There are other concerns with this process, however: one is that high strength peroxide (9%, 12%, or even 35%, for dilution to working solution) becomes hazardous to handle, and is a feedstock for certain improvised products that might lead to a visit from polite people in dark suits with a bulge under one arm, or very impolite folks with shotguns, battering rams, and body armor. Another is that peroxide is a well known bleach for organic pigments and dyes, and might damage the desired image dyes in color film stocks. I haven't been able to find any reports of anyone attempting to bleach color films with peroxide.

Potassium ferricyanide, either directly mixed with fixer or with a halogen donor, is a long-standing process for B&W; Farmer's Reducer and bleaches for color toning and for sepia/sulfide toning depend on this chemical. Kodak apparently once specifically called it out as an alternative bleach for their own color process (it's been rather a long time, though; this might have been for C-22 films). The primary concern with this process is that I've read that specifically Fuji films may experience a reaction that causes the base or one of the filter layers to turn a strong purple when exposed to ferricyanide bleach. This might be compensated with filtration for negative films, but obviously isn't acceptable for chromes.

And now we come to the question: has anyone here actually use either a ferricyanide or hydrogen peroxide bleach process on color films, to be able to report success, failure, or limitations?

 

[Rudeofus]

There are three kinds of bleaches, which can be used for C-41 and E-6:

1. weak bleaches rated for C-41 and/or E-6, such as Ferric EDTA and Ferric PDTA (C-41 only)
2. moderate bleaches, typically based on Ferricyanide
3. powerful bleaches, based on Permanganate, Dichromate, Peroxide or Peracetate

I would seriously discourage people from using any of these "powerful bleaches", since the risk of irreversible emulsion damage is very high. Go look through all these threads about Permanganate bleaches in black&white reversal, for each success story you get at least one report of problems. Some people say "dilute more", others say "lower the temperature", but in the end noone knows how to avoid these issues. Use these bleaches only unless there is absolutely no other option, or if you feel very adventurous.

"Weak bleaches" are on the other end of the spectrum. They will be kind and gentle to your film emulsion, but some ingredients are hard to come by, such as PDTA. EDTA as free acid is also hard to get, but EDTA Disodium Salt is easy to get. If you have EDTA Disodium Salt and e.g. battery acid, you can easily make EDTA yourself. You can also make a bleach from EDTA Disodium Salt directly, but it will be slower. In either case you will need a bleach accelerator, and this is the next tricky part. If you put the bleach accelerator directly into your bleach, you have to be extremely careful with the amount. 0.125 g/l Mercaptotriazole works great, but I honestly don't know, how quickly it depletes during use. If you add too little or too much, bleach will be very slow. Another way to bring in a bleach accelerator is through prebleach, but not everybody is prepared to add yet another bath to the process.

Which brings me to the subject of Ferricyanide bleaches. These were very popular in old times, because they are cheap and easy to mix from readily available ingredients. Even in locked-down Central Europe you could go to a pharmacy and buy Potassium Ferricyanide and Potassium Bromide right now (I do not encourage this, though! Stay at home if you can! ). Neither C-41, nor E-6 films are rated for Ferricyanide bleaches, but I have never even once heard of problems. Ron suggested, that a strong bleach may damage stabilizers in the film, and that problems may show up only decades after processing. Nobody knows for sure.

Conclusion/TLDR: if you can get the ingredients and are willing to play with chemistry, go make a prebleach and an Ammonium Ferric EDTA plus Potassium/Ammonium Bromide bleach. It's the best suited for C-41 and E-6. If you find a decent source of PDTA, use that for C-41, it saves you the prebleach. If you have difficulties getting ingredients and just want to get over with it, Potassium Ferricyanide plus Potassium Bromide is the way to go. If you tell me, which path you plan to pursue, I can post some suitable procedures and formulas.

PS: The easiest and cheapest procedure for C-41 would be getting a BLIX kit, Potassium Bromide and TF-5, using David Lyga's procedure to strech out the color developer, and to use my procedure to convert the BLIX part A into a bleach.

 

[Donald Qualls]

PS: The easiest and cheapest procedure for C-41 would be getting a BLIX kit, Potassium Bromide and TF-5, using David Lyga's procedure to strech out the color developer, and to use my procedure to convert the BLIX part A into a bleach.

I had already given up on being able to get ferric EDTA at reasonable cost. Disodium EDTA looks like an attractive alternative (food preservative, isn't it?), could one use potassium bisulfate as the acid donor instead of battery acid? Most parts stores won't sell the acid packs they use to fill dry charged batteries any more, and the one I've had in my chemical storage for the past twelve years probably isn't to be trusted.

Barring that, I'm aiming for the ferricyanide bleach. I've got the chemicals in hand already, with the possible exception of KBr, and I can get that easily enough. I wouldn't object in any way, however, to knowing methods of stretching color developer and make bleach last longer than BLIX does -- those methods might made C-41 kits more economical.

 

[Rudeofus]

Disodium EDTA looks like an attractive alternative (food preservative, isn't it?), could one use potassium bisulfate as the acid donor instead of battery acid? Most parts stores won't sell the acid packs they use to fill dry charged batteries any more, and the one I've had in my chemical storage for the past twelve years probably isn't to be trusted.

You can easily check both the stash of battery acid you have, and whether potassium bisulfate works: dissolve EDTA Disodium Salt in water, add the acid (or concentrated solution of potassium bisulfate) and see, whether you get a white precipitate. That white precipitate is EDTA free acid. If you can create this EDTA precipitate by any means, you can then filter it out and dry it. This is the EDTA, from which you can then make Ammonium Ferric EDTA with Ferric Chloride and Ammonia.

I wouldn't object in any way, however, to knowing methods of stretching color developer and make bleach last longer than BLIX does -- those methods might made C-41 kits more economical.

David Lyga posted the details, which essentially come down to: dilute C-41 color developer 1+9, then add one milliliter of Sodium Carbonate. He then develops for 8 minutes at 38°C/100°F. While David uses commercial product to mix C-41 CD, you should be able to use Stefan Lange's formula just as well.

Here is a similar soup, mixed from raw ingredients.

 

[Anon Ymous]

@Donald Qualls Your sulfuric acid is probably just fine and I'd prefer it to anything else. If for whatever reason it's not an option, then bisulfate will work fine, I've precipitated EDTA free acid using sodium bisulfate.

When doing the precipitation, have some icy cold distilled, or deionised water at hand. Let the free acid settle at the bottom and try to remove as much liquid as possible. Add a little of the icy cold water and stir, then filter the precipitate with a coffee filter. Wash by adding a bit more of the icy cold water to the filtrate. This should give you a very clean product, with minimal sulfate/bisulfate impurities.

By the way, if the temperature of the solutions is high, then you will likely get a little larger EDTA crystals*, which will be somewhat easier to dry and probably cleaner. Keep in mind though that acid should be diluted and added slowly and very cautiously.

After filtration is complete, put the coffee filter in a plate (that should only be used for things like that) with a lot of paper towels. This will wick much of the water from the filtrate. After this, you can speed drying by putting this on a radiator heater.

Hope this helps.

* Instead of fine powder.

 

[Donald Qualls]

Thanks, guys. Looks like it's back to high school chem -- reactions, filtration, etc. Should probably watch a few RedNile videos on YouTube to prepare. I'll test the sulfuric acid I've got before I order in bisulfate. And now I see that Amazon sells battery acid as well. There's a 6 qt package for under $35 with free shipping; I should get one of those on payday when I order the EDTA, that's about a lifetime supply for everything I do with chemistry. Looks like I'm going to get my darkroom built in the next couple months, so I'll have a place to store stuff like this, as well as room to work without worrying about the dogs getting into things that will kill them.

Also nice to see those single-bath color developer recipes. I'll read down the whole thread to see who got what for accurate color. Color neg is good, but I really like chromes. I've seen people processing E-6 with B&W developer for the first dev, then light fog and into a C-41 process (claiming accurate color). if I can get to the point of being able to process chromes at home, and control cost as well, I'll be a happy fellow and I'll get more use out of my Graphic View and Speed Graphic -- not to mention having to learn to build tiny light boxes to display those 4x5 chromes.

 

[Rudeofus]

If you plan to do your own E-6, take a serious look at Stefan Lange's process. His formulas not only work well, they can all be mixed with compounds available to amateurs.

PS: Be really careful with the filtration of the EDTA, the liquid is very acidic. Try to avoid splashes and have running water nearby. EDTA free acid in water has pH around 1.0, and lots of buffer capacity!

 

[Anon Ymous]

Using a more or less random BW developer as a first developer, followed by a C41 developer, will certainly give you a positive image, but colour balance errors and crossover will be very hard to avoid. These will probably be correctable with digital processing, but not exactly "projection worthy". I second the idea of following Stefan Lange's formulae, for both E6 and C41.

 

[Donald Qualls]

Okay, I skimmed those threads and ones they referenced, I've bookmarked them for later reference and reading when I have more time (after retirement?).

Yep, with having to precipitate the EDTA with sulfuric acid, of course the solute will be pretty acidic. One thing most folks miss in handling sulfuric acid -- the tiniest little drop, even at the 30% battery strength, will make a hole in any cotton cloth that won't show until the next time you wash it. I'll put this off until my darkroom is finished, and remember not to dispose of the solute into the septic tank -- pretty sure the bacteria in there won't like strong sulfuric solutions...

 

[bnxvs]

Hi. If you can get EDTA-Na2 (Trilon B - this reagent is very widely used to soften water and is inexpensive, CAS: 139-33-3), then you can just prepare its iron salt. It's simple - just add iron (III) salt (Ferric chloride for example) - it can be obtained at any store selling goods for radio amateurs. It's used for copper circuit boards etching. If I remember correctly, the ratio of EDTA-Na2 / iron chloride should be 55/45 by weight.

 

[mohmad khatab]

You forgot (quinone) bleach (the great).
With the help and support of Eng. Rudi - Austrian, we managed to make it the official bleaching solution for one of Cairo's most important photographic laboratories.
I will not talk about copper bleach, so some will not get angry.
Speak about this good-hearted solution (quinone bleach ).
It was one of the official bleaching solutions for process (E4) in one era.
It contained a secret material produced by Kodak. The East Germans were able to decipher the talismans of that substance and quinone was used instead with half a gram of copper sulfate.
- A very cheap and effective bleaching solution, but it is wrong for it not to be long, it can live for a maximum of two to 3 months, bearing in mind that the packaging is tightly closed.
- One liter can produce at least 16 negatives, if you use a rotary machine (Jobo) can produce 24 rolls. This was done in practice, and I have evidence and proof of that.
The formula is:
Deionized water 120-130F 800 ml
Glacial acetic acid. 15 ml
sodium acetate 3.5 g
Potassium persulfate 10.0 g
Potassium bromide 10 g
Hydroquinone 0.75 g
Copper sulfate 0.5 g
Water to make 1 liter
Set pH 3.5-4.0 @ 75-77F Allow at least 6 hours for oxidation to quinone before using.
Tips :
First: it gives better results at a temperature of 39 degrees
Second: (pre-bleach) can be used before bleaching and (stopping bath) after bleaching.
Personally, I did this a little and after that, I used a wash with warm running water, the temperature of which should not be less than 39 degrees for a period of at least two minutes before bleaching and at least two minutes after bleaching. The results were excellent.
Update :
There are some hearsay that this solution is not recommended for rotary machines (JOBO).
This information is not accurate.
The time is 8 minutes, the temperature is 39 degrees.
If you use the rotary machine, you will have to extend the bleaching time by one minute per roll after the fifth roll. With temperature increase only one degree.
These tips are based on long experiences with this strange and beautiful solution at the same time.

 

[mohmad khatab]

Using a more or less random BW developer as a first developer, followed by a C41 developer, will certainly give you a positive image, but colour balance errors and crossover will be very hard to avoid. These will probably be correctable with digital processing, but not exactly "projection worthy". I second the idea of following Stefan Lange's formulae, for both E6 and C41.

Where can I get those formulas that you're talking about.
Do you mean those formulas in the forum documents.? As for what?
God bless you .

 

[Rudeofus]

Where can I get those formulas that you're talking about.
Do you mean those formulas in the forum documents.? As for what?

Stefan Lange's formulas can be found here and here.

 

[mohmad khatab]

Stefan Lange's formulas can be found here and here.

Yeah.
you are absolutely right
God bless you.
My greetings.

 

[EdSawyer]

This all seems like an interesting exercise in chemistry and that's cool and all, but it has to be more expensive, more work and with lesser results than just getting the correct products, which are still very much available from multiple vendors...

 

[Rudeofus]

This all seems like an interesting exercise in chemistry and that's cool and all, but it has to be more expensive, more work and with lesser results than just getting the correct products, which are still very much available from multiple vendors...

I can honestly confirm, that home brewing was way more expensive over time, a lot more work, and that I had brief periods with no usable results to show. But I loved doing it and would pursue the same venue over and over again!

 

[mohmad khatab]

Where can I get those formulas that you're talking about.
Do you mean those formulas in the forum documents.? As for what?
God bless you .

I have calculated the costs of this bleach solution.
Deionized water 120-130F 800 ml
Glacial acetic acid. 15 ml
sodium acetate 3.5 g
Potassium persulfate 10.0 g
Potassium bromide 10 g
Hydroquinone 0.75 g
Copper sulfate 0.5 g
Water to make 1 liter
Total costs are (45 Egyptian pounds), approximately 4 USD. It can produce 16 rolls on a roll, which means that the cost of producing a roll is only a quarter of a dollar.
- What are you talking about, sir here?
We had before us many exorbitant recipes that depended on ammonium ferric edta and his companions, but we found all of this is very expensive in relation to the economic conditions in Egypt, and we looked for that formula until it yielded great results.

 

[Donald Qualls]

Apparently Cinestill (cinestillfilm.com) is now offering their "simplified" no-stabilizer C-41 kit in powder form (they claim modern films don't require stabilizer, changed to accommodate mini-labs, which have since virtually vanished). This is a) a little cheaper, currently about $25 for 20 rolls capacity, and b) can be shipped USPS priority as it doesn't have ORM-D restrictions like the liquid kits do. I can't really complain about a buck and a quarter per roll for C-41. Bad new is, as of earlier today, they were out of stock on the powder version...