B&W Reversal with Hydrogen Peroxide

relistan said:

Foma's own datasheets show that the EI of the film varies widely in different developers.

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Are you referring to the curves in page #2 of this document? It is clear from these curves that in none of the developers speed of Fomapan 400 is more than 320.

Coming back to reversal, it would be a pleasant surprise if the emulsion speed of Fomapan 400 in reversal turns out to be 800 or 1000. Of course, this doesn't mean that the film can't be shot 800 or 1000. While the slides may turn out be "acceptable" at 800 or 1000, there will be a loss of shadow detail and to some users and in some situations that might be quite acceptable. As I explained earlier, only a proper test will tell what the emulsion speed is.

relistan said:

If I do an extensive test it will be on Silvermax 100/Scala 160 since I have 200 feet of it.

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This will be real fun. You can also perhaps consider comparing results of your process with the new Scala reversal kit.

Raghu Kuvempunagar said:

Are you referring to the curves in page #2 of this document? It is clear from these curves that in none of the developers speed of Fomapan 400 is more than 320.

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Yes, I know, I said that earlier in the thread. It's between 250-320 for most developers. My point was that the range is already 1/3 stop in common developers so another 1/3 to 400 seems plausible with a very aggressive developer like Multigrade.

Raghu Kuvempunagar said:

Coming back to reversal, it would be a pleasant surprise if the emulsion speed of Fomapan 400 in reversal turns out to be 800 or 1000. Of course, this doesn't mean that the film can't be shot 800 or 1000. While the slides may turn out be "acceptable" at 800 or 1000, there will be a loss of shadow detail and to some users and in some situations that might be quite acceptable. As I explained earlier, only a proper test will tell what the emulsion speed is.

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Yep, not arguing about that at all.

Raghu Kuvempunagar said:

This will be real fun. You can also perhaps consider comparing results of your process with the new Scala reversal kit.

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I thought about that but will probably see how well I can get this working before I do that so I don't get disappointed

So @Donald Qualls and @jnantz asked for a write up of the process I'm using so far. Let's call it version 2. Here you go!

Film:
All tested films so far were 35mm.

• Full process: Fomapan 400 has been tested in the whole process
• Bleaching: Fomapan 400, ORWO N75, Agfapan APX-100 (original)

Chemicals:

• First developer: Ilford Multigrade Developer 1+5
• Second developer: Ilford Multigrade Developer 1+9
• Bleach: Hydrogen Peroxide 3% 300ml + 21ml distilled malt vinegar (white vinegar equivalent)
• Fixer: Ilford Rapid Fixer (any rapid fixer will do). Hardener might be a good idea. I have not tried.

Process:

1. Develop 1. Run the first developer for 12 minutes at 20C. Agitate as you normally would. I invert twice every minute.
   
   
2. Wash at 30C. Use 30C to help keep the film from getting shocked by the jump to 40C in the bleach. Use at least three changes of water. Ilford Multigrade Developer really sticks to film so you may see the first two baths turn yellow. You don’t want to carry that over into the bleach!
   
   
3. Bleach at 40C for about 10 minutes. In theory this can be done totally in the light if the first developers is completely stopped. I wait about 3 minutes into bleaching before opening the tank and then watch to see that the bleach runs to completion. You should see the whole film turn nearly the same color, and a faint positive image. Different films turn different shades of gray. Once nothing else is changing for awhile, you are done. For me this is about 6-10 minutes. Everything after this can be done in daylight! (not bright sun). Note: you must not attempt to do this step in a sealed canister! It will blow the lid off. I agitate 1/minute by rotation rather than inversion since I can't put the cap on.
   
   
4. Wash in the same manner as above, at 30C.
   
   
5. Re-Exposure Take the film from the spool and hold it between your hands, one on each end. Use a tungsten or halogen light and really, really expose it. It’s amazing how much light the film really needs to get fully, absolutely exposed. 1 minute or so is probably enough. Keep the film back about 25-30cm from the light source. You should avoid sunlight or other UV light sources to keep the film from printing out. Additionally, fluorescent lights will likely not give you full exposure.
   
   
6. Develop 2. Run the second developer for 6 minutes at 20C.
   
   
7. Wash in the same manner as above, at 20C

1. Fix per your normal black and white process, at 20C

1. Wash per your normal black and white process, at 20C

I'm going to continue experimenting, but this is what is working.

Pertinent information about the formation of peracetic acid and the amounts present.

https://chemistry.stackexchange.com...etic-acid-and-hydrogen-peroxide-and-its-stabi

It's an equilibrium reaction between acetic acid + hydrogen peroxide == water, peracetic acid. Since we have quite a lot more hydrogen peroxide present, I understand this to mean that the amount of vinegar added will control how much peracetic acid is formed. I suspect there is a certain point where it's too much and is just going to attack the emulsion and your dev tank. Not to mention your safety... Peracetic acid does dissolve silver, as well as copper and gold.

This does however, make me wonder if we can use substantially less peroxide, and replace the volume with water. But I suspect that both hydrogen peroxide and peracetic acid are active as bleach here. I may try it on a film leader to see.

I did a little chemical arithmetic the other night. Pure peroxide, H2O2, has a molecular weight of 34, while anhydrous acetic acid, C2H5OOH is 62. That means you need about 1.8x as much acetic acid by weight as peroxide for a balanced mixture. Correcting for dilution strengths, 3% peroxide and 5% strength acetic acid in distilled vinegar from the supermarket would give an optimum ratio of about 1.8/1.67 = 1.08 -- meaning if you use equal volumes of drug store (chemist, for those in the British sphere) peroxide and supermarket vinegar you have a slight excess of peroxide and should wind up with slightly less than 2% solution of peracetic acid. Adding a little extra vinegar -- say, around 10% more than peroxide -- wouldn't hurt anything; making the bleach acidic is probably preferred (though the peracetic acid formed likely does that anyway).

Ten minutes at 40C is a long time, though. I can get 9% peroxide easily (Amazon will ship it to my door), and in theory I can order 12% strength, and I've got 75% acetic acid on hand, so I can triple the bleach strength trivially -- maybe a bit more, since I'm adding hardly any water with the acetic acid. One should also be able to use indicator stop bath concentrate (you can back-calculate its strength from the dilution and knowing the end product is 2% acetic acid; most of it is 28% strength, as I recall), or of course glacial acetic acid if you're old school enough to keep that around for making up stop bath.

Donald Qualls said:

I did a little chemical arithmetic the other night. Pure peroxide, H2O2, has a molecular weight of 34, while anhydrous acetic acid, C2H5OOH is 62. That means you need about 1.8x as much acetic acid by weight as peroxide for a balanced mixture. Correcting for dilution strengths, 3% peroxide and 5% strength acetic acid in distilled vinegar from the supermarket would give an optimum ratio of about 1.8/1.67 = 1.08 -- meaning if you use equal volumes of drug store (chemist, for those in the British sphere) peroxide and supermarket vinegar you have a slight excess of peroxide and should wind up with slightly less than 2% solution of peracetic acid. Adding a little extra vinegar -- say, around 10% more than peroxide -- wouldn't hurt anything; making the bleach acidic is probably preferred (though the peracetic acid formed likely does that anyway).

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Thanks, this is pretty useful! Question though, since it's an equilibrium reaction, don't you end up with half as much peracetic acid? But maybe I don't quite understand that properly.

Donald Qualls said:

Ten minutes at 40C is a long time, though. I can get 9% peroxide easily (Amazon will ship it to my door), and in theory I can order 12% strength, and I've got 75% acetic acid on hand, so I can triple the bleach strength trivially -- maybe a bit more, since I'm adding hardly any water with the acetic acid. One should also be able to use indicator stop bath concentrate (you can back-calculate its strength from the dilution and knowing the end product is 2% acetic acid; most of it is 28% strength, as I recall), or of course glacial acetic acid if you're old school enough to keep that around for making up stop bath.

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The day after tomorrow I should have some time to do another experiment with more vinegar and then another where I use less peroxide and more vinegar and some water. If you have time to experiment with what you posted I would love to hear about any results.

Donald Qualls said:

I can get 9% peroxide easily (Amazon will ship it to my door), and in theory I can order 12% strength, and I've got 75% acetic acid on hand, so I can triple the bleach strength trivially -- maybe a bit more, since I'm adding hardly any water with the acetic acid.

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Don't want to spoil your fun, but you might want to read what PE wrote on a "perecetic acid bleach composed of 1 litre of 9% hydrogen peroxide (food grade) and 28ml of acetic acid glacial (98%)".

Wow, sure do miss PE. Would love to hear his comments on this, especially since he made a special study of peracetic acid.

This hydrogen peroxide reversal process looks like a fascinating method to reverse B&W film. A lot seems to be going on with it. First, the vinegar is the source of the acetic acid, (acetum is Latin for vinegar). So adding vinegar is adding acid, which of course lowers the ph of the solution. This might make the hydrogen peroxide more reactive; but more importantly, it introduces the acetate ion into the mix.

Hydrogen peroxide (H2O2) will spontaneously decompose into water (H2O) and oxygen (O2) if exposed to the proper catalyst. Metallic silver is such a catalyst. Once you perform the first development you have all this metallic silver which now forms the image on the surface of the film. Adding the H2O2/vinegar solution causes pressure to build up in the tank--probably from all the oxygen released from the hydrogen peroxide once it comes in contact with the silver. Increasing the temperature would cause more oxygen to be released since oxygen gas is less soluble in aqueous solutions at higher temperatures.

Oxygen gas is a powerful oxidizing agent. It plus the hydrogen peroxide would oxidize the acetate ions into peracetic acid. The lower ph plus all the oxidizing chemicals would oxidize the silver atoms (Ag) into silver cations (Ag+) which would form the salt "silver acetate".

Apparently this silver acetate cannot be re-exposed or redeveloped. So it stays as a silver salt until it is fixed out of the film after the second development.

It might be possible to fix the film after the bleach step. Silver acetate is much more soluble than the silver halides generally found in film. Silver acetate is formed out of the negative image which was produced in the first development. So by fixing the film after the bleach step, the more soluble silver acetate salts would dissolve out before the silver halides, (typically AgBr). The silver acetate which forms the negative image would wash away leaving the silver halides which form the positive image behind to be exposed and to form the final--positive--image.

The temperature of the fixing bath might be used to vary the contrast of the final image. A higher temperature should wash out some of the silver halides along with the silver acetate salts. This could reduce contrast. A lower temperature might wash out only the silver acetate ions.

Hydrogen peroxide will soften gelatin next to a metallic silver image. This method has been used to form gelatin reliefs on film. However most commercial films have had the gelatin hardened by chemicals, so loss of gelatin doesn't seem to be a problem.

falotico said:

It might be possible to fix the film after the bleach step. Silver acetate is much more soluble than the silver halides generally found in film. Silver acetate is formed out of the negative image which was produced in the first development. So by fixing the film after the bleach step, the more soluble silver acetate salts would dissolve out before the silver halides, (typically AgBr). The silver acetate which forms the negative image would wash away leaving the silver halides which form the positive image behind to be exposed and to form the final--positive--image.

The temperature of the fixing bath might be used to vary the contrast of the final image. A higher temperature should wash out some of the silver halides along with the silver acetate salts. This could reduce contrast. A lower temperature might wash out only the silver acetate ions.

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To make sure I didn't misunderstand what you wrote, are you recommending a fixing step (thiosulphate?) right after bleaching?! I find this puzzling because this is not usually done in reversal processing when dichromate or permanganate bleach is used. Why's this fixing after bleaching even needed because fixing after second development will remove the silver acetate any way.

falotico said:

H2O2/vinegar solution causes pressure to build up in the tank--probably from all the oxygen released from the hydrogen peroxide once it comes in contact with the silver. Increasing the temperature would cause more oxygen to be released since oxygen gas is less soluble in aqueous solutions at higher temperatures.

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@falotico: This is quite interesting! I wonder if bubbling in an inert gas or CO2, keeping practical considerations aside for now, through the 3% bleach would make it more useful for bleaching the silver image in room temperature by dislodging the dissolved Oxygen from the aqueous medium. Any thoughts on this?

Edit: sorry, I got this inverted. It's a lighter gas like Nitrogen that should be bubbled in to dislodge Oxygen. But the question remains valid. Would it make peroxide bleach more effective at room temperature?

Raghu Kuvempunagar said:

Don't want to spoil your fun, but you might want to read what PE wrote on a "perecetic acid bleach composed of 1 litre of 9% hydrogen peroxide (food grade) and 28ml of acetic acid glacial (98%)".

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Yes, I had read that previously. Basically any acid in enough concentration is a dangerous substance and peracetic acid is a more aggressive oxidizer than sulphuric acid or nitric acid. I don't think you'd want too much of it. Nobody on that thread commented on the fact that the reaction is an equilibrium reaction and again unless I'm misunderstanding, you only get about half the acetic acid converted to peracetic, at most. An interesting aspect is that we actually have a catalyst present: silver. So the reaction may be fairly efficient. I'm not a chemist, this is my layman's understanding.

falotico said:

Wow, sure do miss PE. Would love to hear his comments on this, especially since he made a special study of peracetic acid.

This hydrogen peroxide reversal process looks like a fascinating method to reverse B&W film. A lot seems to be going on with it.

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Thanks for the thinking, @falotico, very interesting. From how I understand the reactions taking place, there are a number of them, as you say. There is the equilibrium reaction between the H2O2 and acetic acid and then H20 and peracetic acid on the other side. There is the reaction between silver halides and H2O2, the reaction between silver halides and peracetic acid, The reaction between free oxygen and silver, the reaction between H2O2 and silver, and a bunch more.

From what I read, silver acetate _is_ light sensitive, but it's also one of the most soluble silver salts. So I am not sure if you need fixer to remove it. If I didn't screw this up, it looks like 1L of water can dissolve a little over 1g of silver acetate at room temperatures. 1g of silver (I know I'm ignoring the acetate mass) seems to equate to something like 1 square meter of film from my research. We're using much less film even for a couple of rolls. So even if all the silver was converted to silver acetate it ought to dissolve entirely in the water present in the bleach or the wash baths afterward, right? But this light sensitivity is actually an argument that maybe bleaching in light is not a great idea. This makes me wonder if the gold colored stain that some people were seeing (which is large silver crystals) is a result of developing silver acetate that did not fully dissolve.

From my understanding of silver as a catalyst in forming peracetic acid, it may also be that a second use bleach actually works faster than the first use? I will try and see.

If you have more insight on any of that, It would be super appreciated. If you can confirm that my understanding of the equilibrium reaction is correct (or totally wrong) that would be also much appreciated.

Raghu Kuvempunagar said:

Don't want to spoil your fun, but you might want to read what PE wrote on a "perecetic acid bleach composed of 1 litre of 9% hydrogen peroxide (food grade) and 28ml of acetic acid glacial (98%)".

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Peracetic acid, which is formed when peroxide is mixed with vinegar, is more toxic than either peroxide or acetic acid. It is also "extremely irritating to mucous membranes of the eyes and nasal passages at low concentrations".

More information on toxicity of peracetic acid.

Raghu Kuvempunagar said:

To make sure I didn't misunderstand what you wrote, are you recommending a fixing step (thiosulphate?) right after bleaching?!

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Yes, I am suggesting a fixing step right after bleaching. Once you bleach with H2O2/vinegar there are two silver salts left in the emulsion: AgBr and AgAcetate, (the trace amounts of AgCl and AgI can be ignored). AgAcetate is about 100,000 times more soluble than AgBr. As relistan suggests in his post today, above, you might be able to fix out all of the AgAcetate with just plain water, although my hunch is that it might take gallons of water. However AgAcetate is soluble in nitric acid but AgBr is not. You might prepare a weak solution of nitric acid either by diluting some that you have or by adding some potassium nitrate to a weak solution of sulfuric acid. I haven't tried it but it could dissolve the AgAcetate efficiently. However this is a strong mineral acid and should be handled with care. Dilute should be VERY dilute; safe even if some should splash.

Since AgAcetate is so soluble in aqueous solutions you might just prepare a dilute solution of normal fixer, thiosulfate, say ten to thirty per cent. It might dissolve the AgAcetate 100,000 times better than it dissolves the AgBr, effectively removing the AgAcetate and leaving the AgBr, (which forms the positive image), behind.

Fixing out the AgAcetate before second development prevents it from becoming re-exposed and fogging the positive image.

relistan said:

From how I understand the reactions taking place, there are a number of them, as you say. There is the equilibrium reaction between the H2O2 and acetic acid and then H20 and peracetic acid on the other side. There is the reaction between silver halides and H2O2, the reaction between silver halides and peracetic acid, The reaction between free oxygen and silver, the reaction between H2O2 and silver, and a bunch more.

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Whoa! Again, would that PE were around to shed some light on this!

Peroxides sometime behave wildly and don't lend themselves to a clear balanced chemical equation. In the emulsion during bleaching a grain of silver metal becomes the center for a lot of different chemical events. The metal acts as a catalyst for the oxygen in the H2O2 to be oxidized to O2 gas. At the same time it acts as a catalyst for the Acetate anion to be oxidized to Peracetic Acid anion--but I don't know if the oxidizing agent is the O2 gas or some weird complex formed on the surface of the silver metal which allows the electrons to dance. This is the stuff of graduate chemistry. While this is going on, the silver metal itself is oxidized to Ag+ and forms the silver acetate salt. Does the Acetate anion come from the Peracetic Acid anion or from free-floating Acetate from the vinegar? There might be an answer out there but be prepared to read a lot of scientific papers.

So, three separate oxidations going on all fueled by H2O2 at a low ph. O- goes to O2 gas; Acetate becomes the Peracetic Acid anion; and Ag metal becomes Ag+. I think I have got this right. If PE were around he would be quick to slam me down if I were wrong. He was a great chemist.

relistan said:

From what I read, silver acetate _is_ light sensitive, but it's also one of the most soluble silver salts. So I am not sure if you need fixer to remove it. If I didn't screw this up, it looks like 1L of water can dissolve a little over 1g of silver acetate at room temperatures. 1g of silver (I know I'm ignoring the acetate mass) seems to equate to something like 1 square meter of film from my research. We're using much less film even for a couple of rolls. So even if all the silver was converted to silver acetate it ought to dissolve entirely in the water present in the bleach or the wash baths afterward, right? But this light sensitivity is actually an argument that maybe bleaching in light is not a great idea. This makes me wonder if the gold colored stain that some people were seeing (which is large silver crystals) is a result of developing silver acetate that did not fully dissolve.

From my understanding of silver as a catalyst in forming peracetic acid, it may also be that a second use bleach actually works faster than the first use? I will try and see.

If you have more insight on any of that, It would be super appreciated. If you can confirm that my understanding of the equilibrium reaction is correct (or totally wrong) that would be also much appreciated.

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A quick scan of the literature on the internet shows that Silver Acetate is about seven per cent as light-sensitive as the AgBr which is already in the film emulsion. And yes, it does form a yellow-colored image so it might be the source of the gold colored stain .

I responded to Raghu Kuvempunagar above about fixing out the AgAcetate. Basically I suggest using some chemical, either thiosulfate or nitric acid, to accelerate the fixing out of Silver Acetate, but I haven't tried this myself. Using plain water might work by itself.

Super interesting, stuff, thanks!

falotico said:

Does the Acetate anion come from the Peracetic Acid anion or from free-floating Acetate from the vinegar? There might be an answer out there but be prepared to read a lot of scientific papers.

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From what I read about peracetic acid, it's normal reaction with compounds is to release the extra oxygen. So if that's what's happening here, peracetic acid reacting with silver forms silver oxide, which will then break down more or less immediately in the solution, releasing the oxygen again. From a lot of reading, but no real chemistry skills, I understand this to mean that any silver acetate is coming from the reaction with acetic acid.

falotico said:

So, three separate oxidations going on all fueled by H2O2 at a low ph. O- goes to O2 gas; Acetate becomes the Peracetic Acid anion; and Ag metal becomes Ag+.

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Sounds plausible to me, but I'm not a chemist

falotico said:

A quick scan of the literature on the internet shows that Silver Acetate is about seven per cent as light-sensitive as the AgBr which is already in the film emulsion. And yes, it does form a yellow-colored image so it might be the source of the gold colored stain .

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Very useful! I had not come across any info about how light sensitive it is, only that it is. I am not, myself, getting a yellow stain and I'm washing with 3 full water changes between bleaching and second developer. In the original video on this thread the slides exhibit staining, and folks in the paper reversal process have seen similar staining working with citric acid. The fact that I am not seeing staining makes me think that most of the acetate is getting washed out. In any case, I think I will try bleaching in total darkness and see if that produces better results.

falotico said:

I responded to Raghu Kuvempunagar above about fixing out the AgAcetate. Basically I suggest using some chemical, either thiosulfate or nitric acid, to accelerate the fixing out of Silver Acetate, but I haven't tried this myself. Using plain water might work by itself.

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I linked this much earlier in the thread, but this chart https://saltlakemetals.com/solubility_of_silver_compounds/ seems to indicate that it's very soluble in water. I know you said it might take gallons to remove. Is that affected by agitation?

EDIT: clearing baths used in other bleaching processes are either sodium sulfite or sodium metabisulfite. Would either of those fit the bill?

Raghu Kuvempunagar said:

Peracetic acid, which is formed when peroxide is mixed with vinegar, is more toxic than either peroxide or acetic acid. It is also "extremely irritating to mucous membranes of the eyes and nasal passages at low concentrations".
More information on toxicity of peracetic acid.

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Yes, agreed. I had read the safety info on it as well. It's commonly used as a disinfectant, though, in concentrations higher than we are using. Caution and safety are one of my goals, though. I don't intend to try to produce high concentrations of it. Maybe slightly higher than I am at now. I am also not clear on exactly how much of it is generated with everything else going on in there.

falotico said:

Wow, sure do miss PE. Would love to hear his comments on this, especially since he made a special study of peracetic acid.

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me too !

he really had an adventurous spirit and I think would be excited that the OP is having fun like this but warn of the non-archival and damage it has the potential of doing to the film...

OP
thanks for the write-up !
John

falotico said:

Yes, I am suggesting a fixing step right after bleaching.

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Very interesting and thanks for the insightful clarification. Interestingly, when using copper sulphate bleach in reversal, we get into a very similar situation. After the bleach step, there are two silver salts in the film - undeveloped silver bromide and rehalogenated silver as silver chloride. In a separate step, similar to the nitric acid step you suggested for peroxide bleach, the bleached film is treated with 2% ammonia solution to fix out the chloride. The fixing step leverages the fact that silver chloride is significantly more soluble than silver bromide in dilute ammonia solutions. In case of peroxide bleach, a short bath in dilute thiosulphate might do the trick as you said though it might also remove some detail in the highlights. I've used copper sulphate bleach on several films after learning about its use in reversal processing from @Athiril and it works quite well except that it is very slow at room temperature.

relistan said:

this chart https://saltlakemetals.com/solubility_of_silver_compounds/ seems to indicate that it's very soluble in water.

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According to this chart, silver acetate is more soluble than silver sulfate, the salt formed when dichromate or permanganate bleach is used. However, when the salts are formed inside the gelatin, there could be other factors beyond solubility that affect how much of the salts are actually removed. Even for dichromate bleach to be effective, Haist says "rates of reaction and movement by diffusion of reactants and reaction products must be harmonized". Further, "if the rate of formation of silver ion exceeds its rate of removal by diffusion from the gelatin emulsion layer into the bath, solubility limits are reached and solids are deposited which are not readily removable in the steps of the process preceding redevelopment". Something like this could also be happening with peroxide bleach.

I have had success with 3% hydrogen peroxide bleach with citric acid and silver nitrate added. But it works at 38C IIRC.

jnantz said:

me too !
he really had an adventurous spirit and I think would be excited that the OP is having fun like this but warn of the non-archival and damage it has the potential of doing to the film...

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Well we won't know for years what potential damage or archival quality there is. Unless the emulsion is damaged a lot, or the binder between emulsion and base is damaged, I am not sure what else could go wrong. I am sure PE could have told me.

jnantz said:

OP
thanks for the write-up !

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No probs! Thanks for following along on the adventure

Raghu Kuvempunagar said:

Very interesting and thanks for the insightful clarification. Interestingly, when using copper sulphate bleach in reversal, we get into a very similar situation. After the bleach step, there are two silver salts in the film - undeveloped silver bromide and rehalogenated silver as silver chloride. In a separate step, similar to the nitric acid step you suggested for peroxide bleach, the bleached film is treated with 2% ammonia solution to fix out the chloride. The fixing step leverages the fact that silver chloride is significantly more soluble than silver bromide in dilute ammonia solutions. In case of peroxide bleach, a short bath in dilute thiosulphate might do the trick as you said though it might also remove some detail in the highlights. I've used copper sulphate bleach on several films after learning about its use in reversal processing from @Athiril and it works quite well except that it is very slow at room temperature.

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This is worth a shot... @falotico, thanks for the idea. I may try a very, very dilute mix, e.g. 1g/L sodium thiosulfate and see what happens.

Raghu Kuvempunagar said:

Haist says "rates of reaction and movement by diffusion of reactants and reaction products must be harmonized". Further, "if the rate of formation of silver ion exceeds its rate of removal by diffusion from the gelatin emulsion layer into the bath, solubility limits are reached and solids are deposited which are not readily removable in the steps of the process preceding redevelopment". Something like this could also be happening with peroxide bleach.

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What would accelerate diffusion from the emulsion without also interfering with bleaching action? A plasticizer? I have some propylene glycol on hand. I know it's quite a weak plasticizer, but maybe worth a try. Or maybe that just makes it worse?

So I have some updates from a bunch of experimenting today. First, the failures to report:

I tried the exact same process with Fomapan R100 and got blank film after the bleach! I had run this in total darkness to see if I could get clearer highlights, so not by inspection as before. This outcome was a real surprise, but some experimenting afterward led me to some interesting outcomes. I thought it was the amount of time in the bleach so I reduced to 6 minutes, in a completely fresh batch of bleach, still in total darkness, and had the same result.

I then clipped off a 2cm section of R100, exposed it to a halogen light, and developed it in the first developer. I then took the blackened film and put it into the newest of the bleach batches in the light. Within about 30 seconds, it was heavily fizzing, something I had not seen before. I believe this is the silver-based anti-halation layer that is specific to R100.

I have a theory: that much bare silver is catalyzing the generation of peracetic acid and that in concentrated, localized amounts is able to eat the gelatin off the film.

That was all at 40C as before. I tried a section of Fomapan 400 in the same manner, in the same bleach. I got MUCH faster bleaching and a similar fizzing reaction after 30-40 seconds. That made me start to think.

Successes to report:

If what has happened is that there is a lot more peracetic acid than before, then maybe I could lower the temperature and try that. I cooled the bleach down to 22C (as much patience as I could manage), and then ran a 5 frames of pictures on Fomapan 400 through the first developer, wash, and bleach. This time I did the bleach by inspection. When I put the roll in, there was a lot of fizzing. I got concerned I'd end up with blank film again, but what the heck, it's an experiment. After about 2 minutes, the fizzing (you can hear it) pretty much went away and by inspection I could see that at 3 minutes, the film was fully bleached! At 22C. It appears that whatever reaction took place with the R100 has noticeably stiffened up the bleaching action. I finished the process on that roll of film and it's hanging to dry. A bit dark, but it was shot under tungsten light (it's getting dark here by 3:45pm) in my Electro 35 GSN which wouldn't have accounted for the slower film rating in tungsten light.

I then took another small clipping of Fomapan R100 and without developing it, put it into the bleach to see if the silver anti-halation layer would dissolve at 22C. It did. I only have this one roll of R100 that I can find (I swear I have more) so I will give it another shot when I've worked out more of the variables.

Follow ups:

1. Does the bleach stay strenghtened? When I get it out next time, has the effect dissipated? (presume yes)
2. Is it possible to bleach R100 at room temperature and not have it go apeshit?
3. Does catalyzing the reaction on purpose at the start make sense? I am thinking a crappy silver spoon or similar.
4. The right way to do this bleaching may be to test a film leader for the film you are going to develop by fully exposing, developing, and bleaching it. Then run the process for that length of time. At least until we've figured more out about how it works.

kentanghk said:

I have had success with 3% hydrogen peroxide bleach with citric acid and silver nitrate added. But it works at 38C IIRC.

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Very interesting! Is the silver nitrate acting as an intensifier?

Interesting! If silver could accelerate the bleach, then the question that arises is why couldn't the silver in the negative image itself act as the accelerator in case of Fomapan 400. Maybe the antihalation layer of Foma 100R has some other stuff besides the silver.