Emulsion softeners

[relistan]

For purposes of attempting to get peroxide bleaches to work better with very hardened emulsions, I want to intentionally try to soften the emulsion ahead of bleaching. The problem with very hardened emulsions (e.g. ADOX Scala/Silvermax or Fomapan R100) is that they are damaged by the escape of oxygen gas during the oxidation process in peroxide bleach. My belief from lots of testing is that the hardened emulsions resist the gas too much, and allow larger bubbles to form before breaking through. This in turn puts large holes in the emulsion (large being relative).

Obviously emulsion softening is a thing that has to be done carefully and I'm sure I will screw up plenty while attempting it. What I'm looking for are chemicals that will have that effect. Please don't try to convince me it's a bad idea. I already think it's probably a bad idea but want to try it and see how bad.

So far I know only of glycerin/glycerine/glycerol depending on where you are from. I have not tried it yet. I did try propylene glycol and isopropyl alcohol, neither of which seem to do much in this regard.

Anything else worth trying? Ideally non-toxic or low toxicity chemicals.

 

[henpe]

Hi

From S. Anchell, "The Darkroom Cookbook" I have the following formula:
---
Water, 750ml
Sodium carbonate, monohydrate, 30gr
Water to make 1.0 litre

To use, soak the print for up to 10 minutes in the solution, agitating occasionally.
---

I have never tested this myself. The description above indicates the softener is intended for prints, but I cannot see why it should not work for negatives as well.

Best regards
Henrik

 

[Bronson Dugnutt]

This is off the top of my head and will likely result in disaster, but consider papaya and pineapple as sources of papain and bromelain, respectively.

Permanganate bleach certainly softens emulsions, but obviously isn't applicable in this case

 

[Raghu Kuvempunagar]

Thiocyanate in the first developer.

 

[Kino]

Have you considered Kodak's Rewashing Formula? This is for rewashing motion picture film and is designed to re-swell the emulsion to allow scratches to "heal" a bit, as well as lift off embedded dirt.

Just a thought...

https://www.kodak.com/content/produ...ssing-KODAK-Motion-Picture-Films-Module-7.pdf

 

[relistan]

I have never tested this myself. The description above indicates the softener is intended for prints, but I cannot see why it should not work for negatives as well.

Thanks! It's worth a shot: it's super simple!

This is off the top of my head and will likely result in disaster, but consider papaya and pineapple as sources of papain and bromelain, respectively.

Wow, can't say I had considered that. I will read up. Thanks!

Thiocyanate in the first developer.

Well, sure Don't have any on hand, but that is definitely a way to do it.

Have you considered Kodak's Rewashing Formula? This is for rewashing motion picture film and is designed to re-swell the emulsion to allow scratches to "heal" a bit, as well as lift off embedded dirt.

Just a thought...

View attachment 265354

https://www.kodak.com/content/produ...ssing-KODAK-Motion-Picture-Films-Module-7.pdf

Very interesting! I did not know about this at all. That's definitely worth a try. Kodak Anti-Calcium No 4 looks like it's sodium tetraphosphate?

 

[Raghu Kuvempunagar]

I'm not sure what a bath in carbonate solution or kodak rewash is going to give you that your first development can't. After all, your first developer is sufficiently alkaline (>= 10.5) and contains potassium carbonate as well as sodium sulphite.

Quoting Haist:

"Alkalis help the gelatin to swell so that the developing agent may penetrate the emulsion layer to the silver halide grain. The function of sodium carbonate in a developing solution was once attributed to the opening of the pores of the gelatin"

"Highly alkaline solutions cause the gelatin of the emulsion layer to swell and soften more than solutions at lower pH."

 

[Kino]

Very interesting! I did not know about this at all. That's definitely worth a try. Kodak Anti-Calcium No 4 looks like it's sodium tetraphosphate?

I am not sure about that; sorry!

 

[relistan]

I'm not sure what a bath in carbonate solution or kodak rewash is going to give you that your first development can't. After all, your first developer is sufficiently alkaline (>= 10.5).

If pH is the only driver, then sure. Is it? If so, why use sulfite and metabisulfite and not borax? Or borax and boric acid? Why sodium carbonate and not sodium hydroxide? Or sodium hydroxide and borax? Presumably there were reasons the chemicals that were selected were chosen. Sulfite is also a pretty special chemical that AFAIK doesn't really have a replacement. I assume that if other alkali worked as well there then they'd have used them?

Also that Kodak anti calc agent No 4 seems like it might be doing more than the name sounds like, from reading about it.

 

[relistan]

I am not sure about that; sorry!

No worries, thanks!

 

[mshchem]

Soak in 38°C water for 15-20 minutes. Not sure if swollen emulsion will change the result.

 

[relistan]

Soak in 38°C water for 15-20 minutes. Not sure if swollen emulsion will change the result.

Agreed, I am not sure either. We will find out.

 

[Raghu Kuvempunagar]

I'm not sure what a bath in carbonate solution or kodak rewash is going to give you that your first development can't.

Quoting from Kodak document that @Kino shared. Italics mine.

"Rewash RW-1 is designed to avoid these sensitometric and dye stability changes, and at the same time to produce similar emulsion swells to that obtained by going through the original developer."

 

[Kino]

Quoting from Kodak document that @Kino shared. Italics mine.

"Rewash RW-1 is designed to avoid these sensitometric and dye stability changes, and at the same time to produce similar emulsion swells to that obtained by going through the original developer."

I would point out that if you swell the emulsion BEFORE you put it in the developer with this solution (of course, giving it a good plain water wash before transfer) then it might make a difference.

Of course, the emulsion could just totally fall-off the base (not likely), but non- critical test images are suggested!

However, until someone tries it, we are just speculating.

 

[relistan]

I am not convinced that swelling and softening are the same thing. We shall see from testing.

 

[grainyvision]

I've done some experiments with swelling/softening for lith printing purposes (trying to eliminate snowballs). It's a tough problem because pH will highly affect swelling, while softening seems to only be possible by destroying the hardening agents used, such as with a strong oxidizer. It's also difficult to determine if your solution is increasing swell or true softening. IF the emulsion is softened, it will be noticeably more slippery (and fragile) when going from an acidic solution, such as citric acid stop bath, directly to warm running water. While excessive swelling will only feel more slippery in a high pH solution and the effect will go away with rinsing. I've had no success in true softening with either carbonate nor lye solutions.

The only thing I've seen reliably soften the emulsion is permanganate bleach. The emulsion being softened means it will swell more and thus becomes much more vulnerable to damage in a high pH developer, but won't feel much different in an acidic solution. It'll also be noticeably more slippery and fragile in a warm water rinse. I've compared this side by side by putting a small drip of the bleach onto one part of the paper and leaving the rest alone. When rinsing under hot water, the part with the drip felt more slippery, however, no noticeable surface change could be noted. When putting the same paper into a highly alkaline solution, it was possible to actually see where the bleach was, it was very slightly raised compared to non-bleached. When using the bleach in traditional reversal process, I could also see and feel when running under a final hot water rinse that the surface had image-wise texture. Black lines were felt to be slightly raised. Permanganate alone could produce this effect but produced stains as well. Sulfuric acid (10%) alone could not produce the effect.

Given that you're trying to soften the emulsion for peroxide bleach though, I assume you're not wanting to introduce permanganate (btw, do not use permanganate + peroxide. Permanganate will destroy the peroxide and in turn be reduced itself in a weird twist of chemistry magic). Unfortunately it seems like you may need to figure out an alternative. Have you tried keeping emulsion swelling as little as possible by using a very strong acid such as sulfuric? Less swelling could mean the bubbles have less far to go maybe and thus cause less noticeable mottling etc??

Edit: and just to note, sulfuric acid is quite the dangerous chemical, but it's not "toxic". It decays into environmentally safe things and once neutralized you could likely drink a solution without much harm. Strong solutions of peroxide are about the same way, and if you don't treat strong peroxide with respect it can leave you more scarred than sulfuric acid might. In otherwords, I wouldn't rule out using sulfuric acid even for a "safe" bleach. Also, there is no need in the common darkroom to be handling concentrated sulfuric acid. I believe it is pointlessly dangerous. Handle prediluted stuff, mine is 40% (10N) for reference. It will likely still give you a nasty burn and you need to treat it with respect, but if you add water to acid accidentally or do something else stupid it's not going to explode in an acidified steam explosion. Adding the solution to water doesn't seem to heat things up at all actually, and I've tested a few things around safety with it. Still handle with care including gloves and eye protection, but diluted sulfuric acid is not nearly as scary as concentrated

 

[relistan]

I've done some experiments with swelling/softening for lith printing purposes (trying to eliminate snowballs). It's a tough problem because pH will highly affect swelling, while softening seems to only be possible by destroying the hardening agents used, such as with a strong oxidizer. It's also difficult to determine if your solution is increasing swell or true softening. IF the emulsion is softened, it will be noticeably more slippery (and fragile) when going from an acidic solution, such as citric acid stop bath, directly to warm running water. While excessive swelling will only feel more slippery in a high pH solution and the effect will go away with rinsing. I've had no success in true softening with either carbonate nor lye solutions.

The only thing I've seen reliably soften the emulsion is permanganate bleach...
...snip...
Unfortunately it seems like you may need to figure out an alternative. Have you tried keeping emulsion swelling as little as possible by using a very strong acid such as sulfuric? Less swelling could mean the bubbles have less far to go maybe and thus cause less noticeable mottling etc??

Edit: and just to note, sulfuric acid is quite the dangerous chemical, but it's not "toxic". It decays into environmentally safe things and once neutralized you could likely drink a solution without much harm. Strong solutions of peroxide are about the same way, and if you don't treat strong peroxide with respect it can leave you more scarred than sulfuric acid might. In otherwords, I wouldn't rule out using sulfuric acid even for a "safe" bleach. Also, there is no need in the common darkroom to be handling concentrated sulfuric acid. I believe it is pointlessly dangerous. Handle prediluted stuff, mine is 40% (10N) for reference. It will likely still give you a nasty burn and you need to treat it with respect, but if you add water to acid accidentally or do something else stupid it's not going to explode in an acidified steam explosion. Adding the solution to water doesn't seem to heat things up at all actually, and I've tested a few things around safety with it. Still handle with care including gloves and eye protection, but diluted sulfuric acid is not nearly as scary as concentrated

Very good points there, and thanks for sharing your experience! Yeah, I am purposely experimenting with peroxide to see how far it could go as a replacement for permanganate. The bleach recipe we've kind of figured out is working great for certain films and abysmally for others. Notably it doesn't work well with the stocks intended as slide films.

I have done quite a bit of experimentation with pH and found that I need to keep it either around 4-4.5 or 8-9 to get good performance bleaching. However, at 8-9 the peroxide breaks down rather rapidly and the bleach does not keep more than about 24 hours. So I run it at about 4.5, which means lowering the pH further to keep swelling down won't work. BUT I think your idea of absolutely keeping swelling to a minimum might be another good path to try. Especially if real softening might be too hard to achieve. @Raghu Kuvempunagar pointed out the very high pH of the paper developer first developer. I could try running an ADOX Silvermax/Scala leader through XTOL, fixing and then bleaching to see if that works better. I believe I did that in the early days of testing the acetic acid/peroxide bleach but I don't have notes about it. I have also run sections of film that had been washed and dried immediately before bleaching. I don't think I've done that with the ADOX film, though.

I will try some of the other ideas above as well and see if anything helps. Thanks!

 

[grainyvision]

Very good points there, and thanks for sharing your experience! Yeah, I am purposely experimenting with peroxide to see how far it could go as a replacement for permanganate. The bleach recipe we've kind of figured out is working great for certain films and abysmally for others. Notably it doesn't work well with the stocks intended as slide films.

I have done quite a bit of experimentation with pH and found that I need to keep it either around 4-4.5 or 8-9 to get good performance bleaching. However, at 8-9 the peroxide breaks down rather rapidly and the bleach does not keep more than about 24 hours. So I run it at about 4.5, which means lowering the pH further to keep swelling down won't work. BUT I think your idea of absolutely keeping swelling to a minimum might be another good path to try. Especially if real softening might be too hard to achieve. @Raghu Kuvempunagar pointed out the very high pH of the paper developer first developer. I could try running an ADOX Silvermax/Scala leader through XTOL, fixing and then bleaching to see if that works better. I believe I did that in the early days of testing the acetic acid/peroxide bleach but I don't have notes about it. I have also run sections of film that had been washed and dried immediately before bleaching. I don't think I've done that with the ADOX film, though.

I will try some of the other ideas above as well and see if anything helps. Thanks!

One potential thing to consider is that with a bicarb/carbonate based first or second developer would react with improper washing (ie, left over acid going into developer or left over carbonate going into bleach) to also form bubbles in the emulsion. It could be worth trying to avoid carbonate in first/second development to eliminate the possibility of this effect happening

 

[Raghu Kuvempunagar]

@relistan: Here's a radically different idea to deal with the original problem of vesiculation due to oxygen bubbles. Instead of bleaching continuously for the whole duration, how about dividing the bleaching process into 3-4 stages? In each stage, we bleach for a shorter duration of time followed by a sulphite clear and water rinse. Any trapped oxygen in the gelatin would be scavenged by sulphite before it forms a big bubble and thereby prevent the formation of holes. It's a simple idea that should be very easy to test as it doesn't require new chemicals or require significant changes in the process.

 

[relistan]

One potential thing to consider is that with a bicarb/carbonate based first or second developer would react with improper washing (ie, left over acid going into developer or left over carbonate going into bleach) to also form bubbles in the emulsion. It could be worth trying to avoid carbonate in first/second development to eliminate the possibility of this effect happening

That's a good point. I am washing quite a bit between steps after finding that even a small amount of carryover can end up with ugly staining and other ill effects. A borax first developer might be interesting.

@relistan: Here's a radically different idea to deal with the original problem of vesiculation due to oxygen bubbles. Instead of bleaching continuously for the whole duration, how about dividing the bleaching process into 3-4 stages? In each stage, we bleach for a shorter duration of time followed by a sulphite clear and water rinse. Any trapped oxygen in the gelatin would be scavenged by sulphite before it forms a big bubble and thereby prevent the formation of holes. It's a simple idea that should be very easy to test as it doesn't require new chemicals or require significant changes in the process.

Interesting idea! I will give it a shot. I suppose it's not possible to put the sulfite in the bleach because it would be oxidized by the peroxide.

 

[Raghu Kuvempunagar]

I suppose it's not possible to put the sulfite in the bleach because it would be oxidized by the peroxide.

That would degrade the bleach as well. What you want is an oxygen scavenger that acts locally in the film while not affecting the bleach. The simple method I suggested earlier hopes to achieve this by separating bleaching from oxygen scavenging.