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C-41 RA Bleach Formula Acetic acid substitution

kyuut

Member
Joined
Apr 8, 2026
Messages
10
Location
Brazil
Format
35mm
Hello!
I’m currently looking into making a PDTA bleach based on the Kodak patent but Acetic acid is extremely restricted here in Brazil.
I’ve been wondering if substituting it with Ammonium acetate as instructed in the ECN-2 PDF would be the best solution,
“One mL of glacial acetic acid is equivalent to 1.05 grams of glacial acetic acid. One millilitre of glacial acetic acid can then be replaced by 1.35 grams of ammonium acetate.”

or if could replace it with Sulfuric or Succinic Acid as i’ve seen it listed in a Flexicolor Bleach iiii RA bottle.
 

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Welcome aboard @kyuut!
Do they sell cleaning vinegar in stores in Brazil? This is a fairly weak solution of acetic acid, usually around 7-10% or so. But that should be enough for your purpose.

I think you could indeed substitute the acetic acid with acetate and a little sulfiruc acid. Then again, it's kind of odd if you can obtain sulfuric acid easily but don't have access to acetic acid.

Either way, note that you don't really need glacial acetic acid. Pretty much any concentration will be fine; you just have to calculate how much to use based on the concentration you can obtain.

Alternatively you could use a simple and cheap ferrocyanide bleach as well. Although it's not really known what this does for the longevity of the negatives, it does work.
 

Thanks Koraks! been reading the forum for a little over an year now but only now registered.

i currently use a ferricyanide bleach with my ECN-2 and C-41 process, but i’m running a very small operation developing film for other people and i’d like to simplify the process (and improve it) Acetic acid used to be easy to get even in glacial form from my research but nowadays anything over 10% generally requires a license from the federal police. from my calculations the minimum i need is 15%, i’ve been inquiring about a 20% solution from one place but i haven’t heard back yet. everyone else requires a license over 5%.
Sulfuric acid can be easily obtained as battery acid here
 
Won't 10% work? What's the concentration you need in the final working strength bleach? And do any of the other ingredients come as a liquid solution?

As to the ferricyanide bleach: do you want to avoid this because of the additional clearing bath?
 
koraks said:
Won't 10% work? What's the concentration you need in the final working strength bleach? And do any of the other ingredients come as a liquid solution?

As to the ferricyanide bleach: do you want to avoid this because of the additional clearing bath?
Click to expand...

it seems i was misremembering and it would indeed work.
515.2ml of a 10% solution to make 1000ml bleach.
this concentration might still require a license but i managed to find cleaning vinegar at a 8% solution. adjusting to 644ml.
i assume this shouldnt be too close to the limit once the other ingredients are dissolved?

this is the formula i’m planning to use:
PDTA 113.6g


2,4-Dihydroxybenzophenon 0.95g


Acetic Acid 80% 64.4 ml


NH4Br 94.67 g


Fe(NO3)3 * 9 H20 136.93

edit: yes, i’d like to remove the clearing bath from my process, and maybe even the vinegar stop bath. the time saved would be substantial i believe. i’d also like to ensure better long term stability since ferricyanide isn’t tested for C-41. i do notice some extra density compared to lab development i’ve gotten in the past but it always scanned fine. haven’t managed to start RA4 printing yet
 
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after further research the 8% cleaning vinegar is the highest concentration i can source. the supplier that had 20% got back to me and it’s not available. other supplies require a license for 10%
 
kyuut said:
i assume this shouldnt be too close to the limit once the other ingredients are dissolved?
Click to expand...
I expect it should work, really. If you have trouble getting everything into solution, warm it all up to 50C or so. But I don't think it'll be an issue even at room temperature if you stir well.
The 8% concentration will likely be just fine. I'd give it a go, see how it works.

My advice is to keep the stop bath so that the pH of your bleach won't drift upwards too much due to developer carry-over.
 
kyuut said:
this is the formula i’m planning to use:
PDTA 113.6g
2,4-Dihydroxybenzophenon 0.95g
Acetic Acid 80% 64.4 ml
NH4Br 94.67 g
Fe(NO3)3 * 9 H20 136.93
Click to expand...

Since you start this with PDTA free acid, you can most likely use Ammonium Acetate instead of Acetic Acid, and just add less Ammonia to get pH to target. The main purpose of Acetic Acid in this mix is its buffering between pH 4 and 5, so Ammonium Acetate will likely work well.

PS: the formula you must must be a very rapid bleach, and you should be able to work with a much diluted version of it. 1+1 and 1+2 would be good starting points, PDTA is not that cheap.
 

Thanks! i just realized i might have mixed up PDTA and DTPA pricing. will confirm once i’m back home
 

i re-checked and 250g of pdta will cost me $60.
still comes out way cheaper. a liter of bleach will cost me $37.50 or so, still 40% cheaper than bellini bleach

PDTA is indeed expensive but i cannot find Ammonium Ferric EDTA for the non RA formula at all.
I was thinking of using the bleach straight. but diluting it could be interesting to try.

i’m also planning on making E6 with the patent formulas you published in the resources page, the current plan is to make the E6 Edta free acid bleach, could i perhaps use it to make a C-41 bleach as well? i’ve read that C-41 bleach will change slide films saturation and contrast so i was planning on having both
 
kyuut said:
i re-checked and 250g of pdta will cost me $60.
still comes out way cheaper. a liter of bleach will cost me $37.50 or so, still 40% cheaper than bellini bleach
Click to expand...

In case you didn't take your posted bleach formula straight from my posting here, I recommend you take a close look at the third formula (mine). This soup is way more dilute, yet reliably bleaches several dozens of rolls per liter. It will degrade over time, I typically toss it after half a year.

With the PDTA prices you listed this may well be the most economical way of producing a decent C-41 bleach.

For RA-4 and E-6 you should use an Ammonium Ferric EDTA based bleach, which has to be more concentrated. I have provided instructions for making one here. You can start with Ammonium Ferric EDTA, if you can't find it with EDTA free acid, and if you can't find this either, with Na2-EDTA or Na4-EDTA, which should be available almost everywhere on this planet.
 

Yes! i took the first formula from your post and also cross referenced the patent a bit. i will check out your personal formula again, would the bleaching time be closer to the 6min Bleach iii? i forgot the exact reason why i didn’t choose that one. it’s been a few weeks since i started my research

The formula with EDTA free acid from the second link is exactly the one i will be using for E6, would that be suitable for C-41 and ECN-2? or should i just keep both formulas?
 
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My own bleach III like concoction definitely does bleach in 6 minutes @38°C/100°F. It may be much faster, but I never bothered to check. Regarding EDTA vs. PDTA: both bleaches last for about 6 months, after which they begin to look messy. By this I don't mean just discoloration, this you will have after the first use. I mean it looks like "the iron is not happy in there any longer and wants to get out". If you process fewer than 20 rolls in this time frame, and if you process E-6 anyway, then a single Ammonium Ferric EDTA based bleach would be your best option.

Both C-41 and ECN-2 are rated for Ammonium Ferric EDTA and the more powerful Ammonium Ferric PDTA. If you don't have E-6 to process, and if PDTA is not much more expensive than EDTA, then the more dilute PDTA bleach is likely the cheaper option, especially, if you also save the bleach accelerator.

If you process more than 20 rolls in six months, and if you have both C-41/ECN-2 and E-6, then a dedicated bleach of each type would probably be the most economic option. With pH adjustment in regular intervals you may keep the E-6 bleach in good shape, maybe even for a whole year.
 

good to know! i've processed over 400 rolls of color film within 12 months, i expect this number to keep rising although 2026 has been a little slow.
the only reason why i haven't moved to commercial C-41 bleach is because it's absurdly expensive here and my small operation doesn't allow that expense yet (still paying for my ATL1500 and such)

PDTA and the other ingredients were easy enough to find so i figured i'd rather make the bleach and use the savings to invest into E6.
E6 is only available in brazil in 2 ways: an alternative metol based formula without Dimezone and HQMS-K in the FD and without citrazinic acid in the CD made by a lab owner friend of mine with another lab, and imported kits which are terribly expensive, the Bellini E6/1 kit available here costs over $200 to develop 10-12 rolls.
although solo and small i'm one of two offering ECN-2 in my state, everyone else is cross processing in C-41.

I got the formula you posted in resources but i'm not sure of what i would need to change to make the EDTA bleach from EDTA free acid for color negative. wouldn't it be too weak without the Mercaptotriazole? EDTA free acid is cheap but in Ammonium ferric form it's impossible to find. PDTA although expensive still makes for a much cheaper bleach than commercial C-41 bleaches. i'm interested in your version and might start with it. since i'm running a rotary process with tons of rinses i believe the lack of 2,4-Dihydroxybenzophenon wouldn't matter. if one day i get a roller transport machine then it likely is better to move to the concentrated formula.

oh and by the way, what's the amount of acetic acid used in your version?
 
kyuut said:
good to know! i've processed over 400 rolls of color film within 12 months, i expect this number to keep rising although 2026 has been a little slow.
Click to expand...

Wow! In this case you should seriously look at replenishing instead of using&discarding. This will require some experimentation, but probably save a lot of money down the road.

kyuut said:
oh and by the way, what's the amount of acetic acid used in your version?
Click to expand...

Wow, I really forgot to put that number 40ml in my formula. it should read:

water 700 ml
PDTA 34g
FeCl3 40% w/w solution 40g
Acetic Acid 80% 40ml
NH4Br 40g

Water ---> 1000ml, pH adjust with NH3 ---> 4.2

@koraks can I ask you to fix that formula in my ancient posting?
 
Rudeofus said:
Wow! In this case you should seriously look at replenishing instead of using&discarding. This will require some experimentation, but probably save a lot of money down the road.
Click to expand...
Yes! i've been reading about aeration and adding bromide but it might make more sense to go straight with replenishment. i assume the RA formula from the patent would use the same rate as the commercial stuff. at 5ml/roll that ends up at $0.18 per roll when converted to USD.
Rudeofus said:
Wow, I really forgot to put that number 40ml in my formula. it should read:

water 700 ml
PDTA 34g
FeCl3 40% w/w solution 40g
Acetic Acid 80% 40ml
NH4Br 40g

Water ---> 1000ml, pH adjust with NH3 ---> 4.2
Click to expand...
Thanks! i'm gonna have to do some thinking but i will likely make your version for a friend of mine that can't afford RA bleach, your version costs about $12 per liter
 
kyuut said:
Yes! i've been reading about aeration and adding bromide but it might make more sense to go straight with replenishment.
Click to expand...
If a bleach does its job, it takes an electron from a silver atom and then ties down the silver ion with a bromide ion. It then passes the electron on to some oxygen atom, which ultimately forms OH-. You lose bromide and add OH-, which means pH also goes up. If pH goes up too much, bleach power drops off a cliff.

So you have loss of bromide, rise of pH, and a third effect will be carry over water coming into your bleach and diluting it.

The perfect match for these three effects will be a bleach, which is more concentrated than the original soup, and which contains some HBr instead of NH4Br. It must not be too low in pH, otherwise the PDTA would fall out.

Due to my low volumes I never experimented with replenishment, but at 400+ rolls/year there should be time&incentive for you to do some testing ...
 

From my research none of the RA Bleaches (i checked Kodak, Fuji and Bellini) have starter solutions which leads me to believe the formula could work as a replenisher for the working solution just like fixer.
I'm certainly no chemist and have at most a basic understanding of things so i could be wrong here. i guess it's worth testing and seeing if i run into retained silver with long term usage with a replenished system, while periodically checking pH.
i'm currently researching about the pH meters available locally since i want to be precise with the E6 formula when i make it. seems like it's gonna be very useful for the bleach too. i did some researching on making the bleach formula posted by PE here and using EDTA free acid and Fe(NO3)3 * 9 H2O (or FeCl₃ 40%) to make Ammonium Ferric EDTA like in your E6 bleach resource page.

EDTA is certainly cheap, i have to figure out if the time savings (45-60 sec) x 6min would add up when my demand starts to increase. at this moment i don't think it would make a big difference as i'm not running multible jobo 2500 tanks yet, but once i am i think it could make a big difference when processing 10+ rolls a day
 
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Bleach compositions don't have to be as accurate as FD/CD, so one may get away without a starter, but replenishment does have to account for the effects of bleaching, which are increasing dilution, rising pH and bromide loss. There is a bleach replenisher recipe posted in that Konica patent. To my surprise it has the same pH as the working solution, but it's definitely more concentrated.

One should also not be too obsessed with bleach pH, with a PDTA based bleach most likely anything between pH 4 and 5.5 will work. PDTA, just like EDTA, is a very good buffer, so some injection of OH- will not change pH all that much. I'd take a close look at the Konica patent to get a starting point for bleach vs. replenisher concentration.

Regarding Ron's formula: it will certainly bleach, and Ron himself stated "it's slow", because he did not include a bleach accelerator. I am not sure, whether 6 minutes bleach time will do the job.

Allow me to provide some more detail about bleach accelerators: they work, but they are a bit difficult. Somewhere around 0.1 g/l Mercaptotriazole was the ideal amount in my tests. Add too much, and bleaching will become very slow. Bleach a few times, and the silver in the emulsion will drag the accelerator out. E-6 solved this by relying on carryover from pre bleach to provide the right amount even with reuse. If you do C-41 or ECN-2, you should either add a small amount of bleach accelerator and accept, that your bleach won't last long, or you accept looooong bleach times, or you use a PDTA based bleach, which doesn't need any of this.
 
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