Copper Sulphate B&W Reversal Bleach

[Donald Qualls]

The very low pH might be bad for certain film emulsions but I'm still convinced it's the permanganate that is abrasive to the emulsion rather than the acid, since dichromate bleach uses similar acid concentration without extensive emulsion damage.

No one (that I know of) has reported film damage from unbuffered citric acid stop bath. Its solution pH is variously reported as low as 2 or as high as about 3.2. Sulfuric acid goes from about 2 if very weak to around 1.2 for solutions of the strength we'd use in copper sulfate or potassium dichromate bleach.

The difference between dichromate, copper sulfate, and permanganate bleaches relative to emulsion is their relationship with proteins. Dichromate has a tanning action -- it crosslinks the proteins in gelatin, hardening the emulsion. Permanganate has the opposite effect, breaking down proteins into smaller chains and softening gelatin. Copper sulfate is closer to dichromate in this regard. Further, permanganate is a very strong oxidizer (potassium permanganate crystals react with fatty substances -- notably glycerin -- rapidly enough to result in combustion).

 

[relistan]

Sounds promising! What film did you test this with, I'm guessing Foma400?

Thanks! Hoping to get some decent shots from this. I tested with a couple of bits of film leader I had clipped from recent rolls. I believe it was Ilford Delta 100 and Agfapan APX-100 (Leverkusen). Ever since I did all that bleach testing at the end of the year I've been saving all the blackened bits of film from development efforts! Saves a lot of time vs having to get dark leaders when testing.

I bought some Foma first developer from Fotoimpex so I will try that and this bleach with some film this weekend when I get a chance.

The very low pH might be bad for certain film emulsions but I'm still convinced it's the permanganate that is abrasive to the emulsion rather than the acid, since dichromate bleach uses similar acid concentration without extensive emulsion damage.

This is what I was nervous about. If it's only 3 minutes, then it might be just fine. I certainly didn't see anything on the little bits I tested with.

Yea, I would be curious on the shelf life of this bleach and how many rolls you can use before it goes bad.

Any evidence on how long this bleach keeps after mixing? One tank, one day, a week, a month, or as long as it stays blue?

Reagent grade mixtures of copper sulfate in distilled water advertise 24 months shelf life. So it doesn't break down in water it seems. The acidity I would think should prevent any mold or bacteria from doing anything. If mold would grow at that acidity, having some dissolved silver should put an end to that. So I would think it's got reasonable shelf life. But I have no idea. That being said, this stuff is so cheap I am not sure it would matter much: you could use it one shot.

I got 1kg of copper sulfate pentahydrate for about €11 shipped to my house from a garden shop. I used Tesco brand salt (€0.44 for 750g), and the citric acid was like €4 for 250g. So even one-shot it's well under €1 per liter. If you were going to mix up just enough for one roll it would be like 25-35 cents depending on 35mm or 120.

Nice! I can get copper sulfate pure enough for our purposes at the Big Box home improvement stores (sold for clearing roots out of drains). I actually have sulfuric acid on hand (30% strength, for battery filling), but I think I have some citric acid, too, and I'd worry less about handling that. ORWO DN21 has a very clear base, I may have to give a try to reversing a test roll.

Yes! I bought some garden supply copper sulfate, exactly. Sulfuric acid is super hard to get here except as concentrated drain cleaner, but citric acid is no big deal at all. Since it's reasonable sized crystals it's way easier and safer to handle.

You should definitely try it out.

 

[YoIaMoNwater]

No one (that I know of) has reported film damage from unbuffered citric acid stop bath. Its solution pH is variously reported as low as 2 or as high as about 3.2. Sulfuric acid goes from about 2 if very weak to around 1.2 for solutions of the strength we'd use in copper sulfate or potassium dichromate bleach.

The difference between dichromate, copper sulfate, and permanganate bleaches relative to emulsion is their relationship with proteins. Dichromate has a tanning action -- it crosslinks the proteins in gelatin, hardening the emulsion. Permanganate has the opposite effect, breaking down proteins into smaller chains and softening gelatin. Copper sulfate is closer to dichromate in this regard. Further, permanganate is a very strong oxidizer (potassium permanganate crystals react with fatty substances -- notably glycerin -- rapidly enough to result in combustion).

Thanks Donald, that’s a great summarization!

Thanks! Hoping to get some decent shots from this. I tested with a couple of bits of film leader I had clipped from recent rolls. I believe it was Ilford Delta 100 and Agfapan APX-100 (Leverkusen). Ever since I did all that bleach testing at the end of the year I've been saving all the blackened bits of film from development efforts! Saves a lot of time vs having to get dark leaders when testing.

I bought some Foma first developer from Fotoimpex so I will try that and this bleach with some film this weekend when I get a chance.

This is what I was nervous about. If it's only 3 minutes, then it might be just fine. I certainly didn't see anything on the little bits I tested with.

Based from what Donald wrote then the pH should not be a problem. That’s nice you got a bunch of developed film leader strips, I remember you had problems with FomaR with the peroxide bleach, maybe that film will work with copper sulphate. You’ll prob have to adjust bleaching time for each films, but curious on your results!

 

[Donald Qualls]

You’ll prob have to adjust bleaching time for each films, but curious on your results!

Most likely, you can just bleach for longer than the slowest bleaching film needs. Generally, you'll take this process to completion (that is, you want to convert all image silver from the first developer to silver chloride so you can dissolve that with the ammonia), and I haven't heard any reports of copper sulfate damaging emulsion, so it ought to be safe to set a time long enough to always get the job done and leave it at that. I'd be surprised if it takes longer than four minutes for any modern silver image film -- which means, even including washes between baths you're only about doubling the time for regular development to get positives. You can do the bleach and ammonia in the light, so you shouldn't need a separate reversal exposure, just wash out the ammonia and go straight to second developer.

 

[Raghu Kuvempunagar]

@Raghu Kuvempunagar how long does the copper sulfate bleach normally take for you? I know you have used it a lot.

I used potassium hydrogen sulphate in place of sulphuric acid using the substitution formula given by Gerry Koch. I never used citric acid. Except for Adox CMS 20 ii which required about 5 minutes, bleach timing was at least fifteen minutes with some films like Carestream Ektascan xray film requiring even longer time. The bleach had a shelf life of at least six months and a capacity of at least ten rolls per litre.

Citric acid is an interesting substitute for sulphuric acid if it works. It might cause mould formation as it does in copper toner. So I would not be too optimistic about long shelf life.

About the ammonia clearing step, 2-3% ammonia solution hardly takes 2-3 minutes to remove the bleached image. The solution can be reused but becomes muddy after one or two uses.

I didn't notice any emulsion damage due to either copper sulphate bleach or ammonia clearing. However, the bleach should be filtered after use.

BTW I used lab grade sodium chloride as the cooking salt might have impurities such as iodide.

 

[Rudeofus]

Citric acid is an interesting substitute for sulphuric acid if it works. It might cause mould formation as it does in copper toner. So I would not be too optimistic about long shelf life.

While Citric Acid alone is certainly very conductive to mold growth, the copper ions will stop any mold in its tracks. The only long time shelf life risk I see to this bleach is, that copper may - over time - oxidize the Citric Acid.

 

[Raghu Kuvempunagar]

While Citric Acid alone is certainly very conductive to mold growth, the copper ions will stop any mold in its tracks. The only long time shelf life risk I see to this bleach is, that copper may - over time - oxidize the Citric Acid.

I never used citric acid in copper sulphate bleach but I've observed mould formation in copper toner. Maybe it is due to the warmer temperatures in this side of the world.

 

[YoIaMoNwater]

Most likely, you can just bleach for longer than the slowest bleaching film needs. Generally, you'll take this process to completion (that is, you want to convert all image silver from the first developer to silver chloride so you can dissolve that with the ammonia), and I haven't heard any reports of copper sulfate damaging emulsion, so it ought to be safe to set a time long enough to always get the job done and leave it at that. I'd be surprised if it takes longer than four minutes for any modern silver image film -- which means, even including washes between baths you're only about doubling the time for regular development to get positives. You can do the bleach and ammonia in the light, so you shouldn't need a separate reversal exposure, just wash out the ammonia and go straight to second developer.

Some modern film emulsions are very thick and you’ll be surprised the time it takes to fully bleach one. For example, I’ve recently worked with TriX and even 10 min permanganate bleach wasn’t enough. Granted I’ve use less amount of permanganate (0.12% w/v) than usual but the only film that was fully bleached in a short time frame was TMax100 in around 4 min.

 

[Raghu Kuvempunagar]

Some modern film emulsions are very thick and you’ll be surprised the time it takes to fully bleach one.

Any modern C41 film developed in B&W reversal first developer takes a good amount of time to bleach. BTW Fuji Superia films make very nice monochrome slides when reversal processed albeit with a slight yellow tint.

 

[relistan]

I used potassium hydrogen sulphate in place of sulphuric acid using the substitution formula given by Gerry Koch. I never used citric acid. Except for Adox CMS 20 ii which required about 5 minutes, bleach timing was at least fifteen minutes with some films like Carestream Ektascan xray film requiring even longer time. The bleach had a shelf life of at least six months and a capacity of at least ten rolls per litre.

Thanks for all the info, Raghu! I am seeing decent times with the citric acid. Will post in a few minutes.

While Citric Acid alone is certainly very conductive to mold growth, the copper ions will stop any mold in its tracks. The only long time shelf life risk I see to this bleach is, that copper may - over time - oxidize the Citric Acid.

This makes sense. My theory was also that once some silver is dissolved in there that will kill any mold as well. I know your fixer recipe works like that. I've had that fixer for months and it has been fine.

Any modern C41 film developed in B&W reversal first developer takes a good amount of time to bleach. BTW Fuji Superia films make very nice monochrome slides when reversal processed albeit with a slight yellow tint.

Very interesting. I have what might as well be a billion feet of Vision3 200T. Might be worth trying.

 

[Raghu Kuvempunagar]

My theory was also that once some silver is dissolved in there that will kill any mold as well. I know your fixer recipe works like that. I've had that fixer for months and it has been fine.

Sorry, you're mistaken. Copper sulphate bleach is a rehalogenating bleach; it doesn't dissolve silver. Rather it converts silver to silver chloride which remains on the film and needs to be cleared in a subsequent step using 2% ammonia.

 

[relistan]

So I got stuck doing taxes today (fun, fun!) and didn't get to shoot any frames like I wanted. However, I got about 2 hours to run some further experiments with the Copper Sulfate/Salt/Citric acid bleach I posted.

I am using Copper sulfate pentahydrate from the garden shop. The salt is Tesco brand. It is not iodized. It's substantially all sodium chloride but does contain sodium ferrocyanide (not ferri) as a caking agent. I am not sure how much ferrocyanide ion is present in the bleach. Presumably a very tiny amount.

Pretty happy with the result.

Here's what I did:

1. Developed a leader of Ilford Delta 100 for 7 mins in my old Ilford Multigrade-based first developer (MG 1+5 with 1.5g/L sodium thiosulfate)
2. Because I am testing the bleach and not trying to test dev times for the first developer, I fixed for 3 mins
3. I bleached for 5 mins @ 19C followed by 2 mins in 2.5% ammonia at 19C
4. Skipped the clearing bath. It seems to have no effect in my testing so far.
5. Redeveloped for 5 mins in Ilford Multigrade 1+9

Result:

Film base seems to have a slight pink cast.

When first mixed up with just the salt and the copper sulfate, the bleach is quite cloudy. When the citric acid is added, it looks like this:

Note that I mixed it in the 1L stainless, but moved it to plastic after. The bigger container is nicer for mixing and it doesn't get scratched by the crystals.

 

[Raghu Kuvempunagar]

Pretty happy with the result.

I've always been pleased with the results I got from copper sulphate bleach on a variety of films. It's not as convenient as dichromate bleach and the smell of ammonia is not nice, but it does give good results.

 

[relistan]

Sorry, you're mistaken. Copper sulphate bleach is a rehalogenating bleach; it doesn't dissolve silver. Rather it converts silver to silver chloride which remains on the film and needs to be cleared in a subsequent step using 2% ammonia.

Yes, it is a rehal bleach. But earlier in this same thread, PE said (https://www.photrio.com/forum/threads/copper-sulphate-b-w-reversal-bleach.137943/page-3#post-2178698)

"Remember that any bleach containing Ammonium ion or Chloride ion is also, to some extent, a blix. This will cause loss of AgX in the remaining positive image in reversal B&W."

My understanding is that a small amount of silver is indeed being dissolved. Of course, the chloride itself may be enough to prevent mold.

 

[Donald Qualls]

The solubility of silver chloride is non-zero, but it's very small. This means only very little silver can dissolve in copper sulfate bleach without precipitating as silver chloride. In practice, this formation of silver chloride (in place, replacing image silver) is exactly what we're trying to accomplish here, but there won't be enough silver ion left in the solution to have much effect.

I don't know how to reconcile a long shelf life for copper sulfate bleach made with citric acid against moldy copper toner solution -- but dissolve silver probably isn't a significant factor.

 

[Raghu Kuvempunagar]

Y
"Remember that any bleach containing Ammonium ion or Chloride ion is also, to some extent, a blix. This will cause loss of AgX in the remaining positive image in reversal B&W."

If there were indeed loss of AgX in the positive halide image due to the use of copper sulphate bleach, then it would have severely affected the shadows causing substantial loss of shadow detail. This is not what I noticed but something you can independently verify. I really doubt any noteworthy halide depletion happens because of the copper sulphate bleach.

OTOH extended time in ammonia can indeed deplete the halide image as PE pointed out. Silver bromide is soluble in ammonia and given sufficient time, it will dissolve.

 

[relistan]

If there were indeed loss of AgX in the positive halide image due to the use of copper sulphate bleach, then it would have severely affected the shadows causing substantial loss of shadow detail. This is not what I noticed but something you can independently verify. I really doubt any noteworthy halide depletion happens because of the copper sulphatE

Do you notice the loss from developers containing sulfite? No. Because it takes a reasonable amount of dissolved silver to affect the resulting density.

Regardless, we don't really need to argue the point given that I am not sure any of us knows for sure. We'll see how the bleach lasts from testing. Given the other chemicals I have mixed up using citric acid I'm not too worried. And as I pointed out earlier, it's so cheap that lifespan doesn't really matter. The ammonia bath is likely to need to be replaced first.

 

[Raghu Kuvempunagar]

we don't really need to argue the point given that I am not sure any of us knows for sure. We'll see how the bleach lasts from testing.

+1

 

[NedL]

I like the idea of using citric acid in place of sulfuric acid or sodium bisulfate, but still worry about disposal or storage of the ammonia w/ AgCl. Maybe I am too cautious. I'd like to try this with paper negatives.

 

[Raghu Kuvempunagar]

I'd like to try this with paper negatives.

Copper sulphate bleach with ammonia clear is not suitable for reversing photographic paper that contains silver chloride in the emulsion. Note that copper sulphate bleach converts the negative image into silver chloride and ammonia removes all silver chloride without discrimination.

 

[Raghu Kuvempunagar]

still worry about disposal or storage of the ammonia w/ AgCl. Maybe I am too cautious.

I would like to understand the risk and would appreciate your insights into the subject. Does the risk reduce if 2% ammonia is used only once to clear the chloride from the bleached film and disposed right after the use?

 

[Rudeofus]

I never used citric acid in copper sulphate bleach but I've observed mould formation in copper toner. Maybe it is due to the warmer temperatures in this side of the world.

I have never had Copper Toner working solution last more than a few hours, therefore I would not expect to observe mold growth in working solution. Which recipe did you use?

 

[relistan]

I did a little test today, trying out something @Rudeofus asked about on this thread a few years ago. I mixed up an 8.5% solution of ammonium chloride, which if I did the math properly, should have a little more ammonia present than the 2.5% solution I was using. Result: It may have every so slightly dissolved some. I am not convinced it would ever dissolve. Of course, a stronger solution is possible to mix and might still work. I am not enough of a chemist to know why this wouldn't work. My guess is that all the chloride from the ammonium chloride prevents the silver chloride from dissolving by preventing the reaction from happening (equilibrium reaction?).

I also did some slides, but my first developer was not strong/long enough and they are dark and not worth showing.

 

[Rudeofus]

These 8.5% Ammonium Chloride, were these indeed 85 g/l ?

With Ammonia, you have an ingredient, which just complexes silver ions to form a soluble compound. With chloride and silver, you create a balance between insoluble Silver Chloride and soluble silver chloride complexes of the [AgCln+1]n- form. With little chloride in the mix, the balance will tilt towards insoluble Silver Chloride, that's, why Sodium Chloride works as restrainer in RA-4 color developer. With lots of chloride in the mix, you get silver solvent behavior, c.f. Microdol.

I would therefore suspect, that much higher concentrations of NH4Cl would give much better solvent behavior. If you have a cheap source of Ammonium Chloride and are willing to experiment, then I'd suggest 200 g/l or more Ammonium Chloride as a next test.

 

[relistan]

These 8.5% Ammonium Chloride, were these indeed 85 g/l ?

With Ammonia, you have an ingredient, which just complexes silver ions to form a soluble compound. With chloride and silver, you create a balance between insoluble Silver Chloride and soluble silver chloride complexes of the [AgCln+1]n- form. With little chloride in the mix, the balance will tilt towards insoluble Silver Chloride, that's, why Sodium Chloride works as restrainer in RA-4 color developer. With lots of chloride in the mix, you get silver solvent behavior, c.f. Microdol.

I would therefore suspect, that much higher concentrations of NH4Cl would give much better solvent behavior. If you have a cheap source of Ammonium Chloride and are willing to experiment, then I'd suggest 200 g/l or more Ammonium Chloride as a next test.

Thanks for the info. This makes sense.

Indeed, yes I mixed 8.5g of ammonium chloride into 100ml of total solution (water), which is more than enough for testing on these little strips of film I was working on. I don't really have a lot of ammonium chloride left so I may just order some more to try out your suggestion.