B&W Reversal with Hydrogen Peroxide

[relistan]

Interesting, this is the free acid, not a Na salt. This is very useful to those who would like to scratch mix some E6 bleach, combined with some ammonia, ferric nitrate and ammonium bromide.

Ah, bummer, they only ship to Ireland/UK

Ah sorry I didn't realize. Well, DM me if you want some, I have 1kg and I don't need 1kg.

 

[Lachlan Young]

I only have one source for Calgon Photo that I know about in Europe (Suvatlar/Moersch)

It's Sodium Hexametaphosphate - many other photochemical suppliers carry it - I mentioned it because it might be worth picking up if you're buying other stuff from Suvatlar for bleaches.

 

[Anon Ymous]

Ah sorry I didn't realize. Well, DM me if you want some, I have 1kg and I don't need 1kg.

Thanks for the offer, highly appreciated, but I don't need some right now. Actually, you can fairly easily make the free acid out of the sodium salts, but it's just not as easy as scooping the amount you want from a bag.

 

[Raghu Kuvempunagar]

@kentanghk
It does have a stain remover, but as I quoted earlier in the thread, they did not find it necessary with the supplied bleaches.

Note that the film used by the inventors of that Konica patent is different from the one our @kentanghk is using in his experiments. Clearly, there is some stain in his results and a stain remover might be necessary for the film he is using. I guess severity of stain will vary with films and the amount of EDTA used.

 

[kentanghk]

I picked EDTA originally because it's very easy to get, I think just about anywhere. I only have one source for Calgon Photo that I know about in Europe (Suvatlar/Moersch) but EDTA I just ordered in a 1 kilogram bag delivered. It's used in tons of cleaning products and detergents. HEDP is much harder to get. The brand name of EDTA that I ended up with is "Dissolvine Z". It is technical grade. I am guessing Kentanghk is using a better grade. We'll see how it works.

I am using reagent grade but I guess technical grade will work perfectly fine. The only problem IMHO is poor water solubility of EDTA free acid but I believe it can be easily converted to NaEDTA by sodium hydroxide.

 

[YoIaMoNwater]

@kentanghk nice work! Seems like you have optimized the concentration of EDTA needed. Can you try adjusting the pH to see if it has an effect on bleaching?

I picked EDTA originally because it's very easy to get, I think just about anywhere. I only have one source for Calgon Photo that I know about in Europe (Suvatlar/Moersch) but EDTA I just ordered in a 1 kilogram bag delivered. It's used in tons of cleaning products and detergents. HEDP is much harder to get. The brand name of EDTA that I ended up with is "Dissolvine Z". It is technical grade. I am guessing Kentanghk is using a better grade. We'll see how it works.

Nice! Just be aware that if you're getting the free acid EDTA then it will only dissolve in high pH (we make a lot of 0.5M EDTA in our lab and at this concentration it will only dissolve at pH 8). The salt version (K2 EDTA) is more soluble and doesn't require pH adjustment for it to dissolve in water.

 

[relistan]

Nice! Just be aware that if you're getting the free acid EDTA then it will only dissolve in high pH (we make a lot of 0.5M EDTA in our lab and at this concentration it will only dissolve at pH 8). The salt version (K2 EDTA) is more soluble and doesn't require pH adjustment for it to dissolve in water.

Good to know. Thanks! If I can't get it to dissolve I could add some NaOH like @kentanghk said. Would borax work? Seems ok pH-wise but not sure if it will react with the EDTA weirdly.

 

[relistan]

Note that the film used by the inventors of that Konica patent is different from the one our @kentanghk is using in his experiments. Clearly, there is some stain in his results and a stain remover might be necessary for the film he is using. I guess severity of stain will vary with films and the amount of EDTA used.

True, they were using color film, which would have the orange mask and possibly completely hide such a tiny amount of staining.

 

[relistan]

I am using reagent grade but I guess technical grade will work perfectly fine. The only problem IMHO is poor water solubility of EDTA free acid but I believe it can be easily converted to NaEDTA by sodium hydroxide.

I didn't know about this and now I'm looking at how to make that work. Was hoping to not have to mess with NaOH but looks like I have to if I want to dissolve this. Too bad because the same place sells the tetrasodium salt but I thought that's not what I wanted. I am trying to find solubility information for other solvents like alcohol or propylene glycol, maybe that's possible.

 

[kentanghk]

@kentanghk nice work! Seems like you have optimized the concentration of EDTA needed. Can you try adjusting the pH to see if it has an effect on bleaching?

Sure! I'll try to test it next week.

Good to know. Thanks! If I can't get it to dissolve I could add some NaOH like @kentanghk said. Would borax work? Seems ok pH-wise but not sure if it will react with the EDTA weirdly.

I am not 100% sure but if the EDTA free acid can be dissolved at pH 8 as @YoIaMoNwater suggested, maybe a solution of sodium carbonate or bicarbonate will do the job?

 

[Anon Ymous]

@relistan @kentanghk Yes, sodium carbonate, or bicarbonate can be used instead of hydroxide. You are essentially making EDTA sodium salts one way or another. The only difference is that (bi)carbonate will also produce a little bit of carbon dioxide too.

 

[kentanghk]

I bleached and fixed a stained film strip from previous experiment in flexicolor chemical. The stain was removed. I guess this support the theory that the ugly stain we encountered is elemental silver.

 

[Raghu Kuvempunagar]

I bleached and fixed a stained film strip from previous experiment in flexicolor chemical. The stain was removed. I guess this support the theory that the ugly stain we encountered is elemental silver.

In the results you presented, more EDTA used in the peroxide bleach less is the stain. May be EDTA is able to sequester the silver ions trapped in the gelatin and thereby prevent the reformation of silver. You may want to increase the concentration of EDTA further and see if it can completely inhibit stain formation.

 

[Lachlan Young]

C-41/ Flexcolor bleach uses Ferric Ammoniumn PDTA as far as I know.

Essentially, chelated ferric ions oxidise the metallic silver, making soluble silver ions that can then be washed out.

 

[relistan]

Well I had some disappointing results today. Having the free acid EDTA instead of the salts makes it so much more complicated than just dissolving the EDTA into the bleach.

I first attempted to mix up a 6.4% EDTA solution using sodium carbonate to get the pH up high enough to dissolve it. I could not get it to completely clear, so I filtered it and then tried this solution with just peroxide (20ml 3% peroxide, 2ml ~6.4% EDTA solution) to see if that worked at all. It did not: no bleaching to see in 10 mins. It might work with more EDTA.

I then started with some of the seasoned peracetic acid bleach I had been using and used 20ml of that and 2ml of the 6.4% EDTA (carbonate). If I haven't screwed up calculating, with dilution I think that works out to 0.58g/L which is a tiny bit more than the lowest concentrate sample that @kentanghk tried. I compared this to the existing peracetic acid bleach to see how it performed. At room temperature (20C), I bleached a small piece of Fomapan 400. When fully bleached in about 3 minutes, both looked reasonably clear, but I could see sort of "flow" outlines on the EDTA sample, just like @kentanghk saw on the lower concentration samples he tested. When I redeveloped the samples, the original bleach sample was clear, no staining. The sample with EDTA turned quite dark!

I thought maybe this was the same thing I saw with percarbonate: maybe it's forming silver carbonate, which is light sensitive and thus darkens when redeveloped. So I decided I had better get some NaOH instead. Since I didn't have any on hand, the only thing I could get on short notice (i.e. today) under lockdown was to get Caustic Soda from the hardware store by my house. This is labeled as being only sodium hydroxide. The MSDS for this brand only lists sodium hydroxide. I then mixed up a 6.4% solution and tried again. This had no problem clearing fully.

Hopefully I didn't screw up calculating that. This is what I did:

• 500ml room temp tap water
• 16g of sodium hydroxide
  
• 32g of EDTA free acid
• pH about 9 (litmus paper)

I think this gives me 0.109 moles of EDTA (32 / 292.24 g/mol) and 0.40 moles of sodium hydroxide (16 / 39.997 g/mol). Out of that I should be getting EDTA-4Na or EDTA-2Na in solution if I have that right.
When mixed:

• The peracetic acid bleach was pH 4 or so (litmus paper)
• The peracetic acid/EDTA bleach was pH 5 or so (litmus paper)

Bleached for 5 minutes at room temp ~20C.
What I got was the exact same problem. I used tap water to mix it and so there is a possibility it's a small amount of chlorine from the tap water. Or more probably the caustic soda I got also contains sodium carbonate. I would have thought that it would require labeling if so. When I washed the bleached film, a bit of black came off in the water, almost looked like remjet. When I put it into the developer, a bit more came off. Maybe silver carbonate deposited on the film? It was not emulsion coming off, the emulsion is still there, and quite stained.

This was about 4 hours end to end, including a trip to the hardware store. I may have a little more time tomorrow to try to use deionized water as a possible improvement in case it's tap water.

I think the photo disguises a bit just how dark the top sample is. It's not just stained.

Anyone have any better ideas about this black deposit?

 

[relistan]

I bleached and fixed a stained film strip from previous experiment in flexicolor chemical. The stain was removed. I guess this support the theory that the ugly stain we encountered is elemental silver.

Good to know!

 

[kentanghk]

When I redeveloped the samples, the original bleach sample was clear, no staining. The sample with EDTA turned quite dark!

That's interesting. Maybe the EDTA version need more time for complete bleaching? I skipped second development in my previous test so I might have the same problem but I just ain't aware of it.

Or more probably the caustic soda I got also contains sodium carbonate.

Sodium hydroxide do absorb carbon dioxide in air to form sodium carbonate but it should not cause problem unless our EDTA bleach is super sensitive to carbonate.

 

[relistan]

Sodium hydroxide do absorb carbon dioxide in air to form sodium carbonate but it should not cause problem unless our EDTA bleach is super sensitive to carbonate.

Thanks! I’m betting on tap water as the issue then. The other bleach has no tap water in it. I will try with deionized water (I can’t get distilled water easily).

 

[Raghu Kuvempunagar]

If @Team ADOX can supply world wide the bleach of its Scala reversal kit separately and in larger quantity, it would be doing a great favor to those reversal enthusiasts who prefer not to use dichromate bleach.

 

[Lachlan Young]

If @Team ADOX can supply world wide the bleach of its Scala reversal kit separately and in larger quantity, it would be doing a great favor to those reversal enthusiasts who prefer not to use dichromate bleach.

I don't think it's anything significantly more special than the Agfa patent - ie permanganate, sulphuric acid, and the hexametaphosphate to sequestrate the manganese.

 

[Raghu Kuvempunagar]

I don't think it's anything significantly more special than the Agfa patent - ie permanganate, sulphuric acid, and the hexametaphosphate to sequestrate the manganese.

That's what I had guessed by color of the bleach but Adox seems to have managed to dilute the bleach enough to fly below the hazards radar. MSDS for the reversal kit didn't have a section on the bleach!

 

[Lachlan Young]

That's what I had guessed by color of the bleach but Adox seems to have managed to dilute the bleach enough to fly below the hazards radar. MSDS for the reversal kit didn't have a section on the bleach!

If you go back & check the patent, it suggests that if you accept a longer bleaching time, the bleach doesn't need to have a particularly low pH - which also (I suspect) is beneficial in reducing the potential for emulsion damage. The amount of permanganate is tiny - 0.2% in the Agfa patent - even if you raise it to the concentration of the Adox kit, it's likely not essential to list it. And the hexametaphosphate is not significant - so it's obvious that with a bit of reasonably smart chemical engineering, you can make an adequately safe reversal bleach - if you don't need an ultra high throughput or high speed bleaching.

 

[relistan]

So, I tried this today with deionized water:

• 12.8% solution EDTA — 2ml (hardware store caustic soda (NaOH) and EDTA free acid)
  
• Peracetic acid bleach as before — 20ml
• pH about 4

This should get me about 1.2g/L EDTA in the final bleach. 10 minutes of bleaching and that was not adequate. I did not detect any of that black deposit that I had seen before so I think the problem must be something in my tap water. However, although the film looked clear, it developed back down quite dark. @kentanghk when you are next in the lab would you mind redeveloping one of the strips you bleached to see if you see the same effect? It's still possible that I'm doing something wrong and it has nothing to do with adding EDTA.

I have also made an attempt to add 1 drop of ADOX Adoflo to the bleach to see if it makes any difference on emulsion damage. My thinking was that the bigger damage may happen behind the bigger bubbles and that getting the bubbles to release from the surface of the emulsion sooner might lead to less damage. I will post results later when I have analyzed the strips with a loupe. I also took two short videos of the difference in behavior because it's quite noticeable.

 

[Raghu Kuvempunagar]

If you go back & check the patent, it suggests that if you accept a longer bleaching time, the bleach doesn't need to have a particularly low pH - which also (I suspect) is beneficial in reducing the potential for emulsion damage. The amount of permanganate is tiny - 0.2% in the Agfa patent - even if you raise it to the concentration of the Adox kit, it's likely not essential to list it. And the hexametaphosphate is not significant - so it's obvious that with a bit of reasonably smart chemical engineering, you can make an adequately safe reversal bleach - if you don't need an ultra high throughput or high speed bleaching.

This is entirely plausible. Interestingly, MSDS of a commercially available 0.01M solution of potassium permanganate (which is 1.6g of permanganate/liter) product says "not classified as a hazardous chemical."

 

[kentanghk]

However, although the film looked clear, it developed back down quite dark. @kentanghk when you are next in the lab would you mind redeveloping one of the strips you bleached to see if you see the same effect? It's still possible that I'm doing something wrong and it has nothing to do with adding EDTA.

The bleached strips were milky in my previous test and that's why I fixed them. I thought it was undeveloped silver halide but if the film bleached with peracetic acid bleach without EDTA did not turn black in second development, something else may be happening here.

Film strip after bleaching. It turned clear after fixing.