Wanting to try reversal processing but also not die

Raghu Kuvempunagar · Jul 14, 2020

I would be surprised if anyone has really used 3% peroxide bleach in reversal processing of B&W film successfully. My own experiments with 3% peroxide bleach gave unsatisfactory results. Firstly, it took hours to remove the silver. Secondly, not all silver was removed. Thirdly, it attacked the film base itself with pinholes forming.

The only reports of success I'm aware of is with much higher concentration. And as @Lachlan Young pointed out, at such concentrations, peroxide is no longer safe.

If one doesn't want to deal with either dichromate or permanganate, @Athiril's copper sulphate bleach idea is worth considering. Though slow (10-30 minutes depending on the film), it's quite effective, has good capacity, and is economical.

grainyvision · Jul 18, 2020

It's far from a trivial process, but yesterday I made "direct positive" prints by using fairly common developer chemicals and nothing else. It uses the concepts that Kodak's thermal development patents kinda hinted at, with developer inhibition and exhaustion being used to control how a fogged emulsion develops

The process is basically, one sheet of paper is fogged completely in daylight. The other sheet is exposed to the image from an enlarger. Both sheets are rinsed to remove incorporated developers, then the fogged sheet is put into an inactive developer solution (I used a little bit of hydroquinone and ascorbic acid). The negative image sheet is put into an activator solution (I used sodium hydroxide but carbonate might've worked if using a different developer). The two sheets are carefully removed, ensuring they aren't dry but also not dripping, and are then sandwiched together emulsion-to-emulsion. I used glass on top of the paper to ensure they're perfectly married, but I'm not sure it helped. Finally, after 1 minute I carefully peel up the sheets and quickly separate them and dunk them into stop bath and then fix them. The result is a negative and a positive image. As you can see from the attached example though, getting the two sheets to be perfectly sandwiched without bubbles is no trivial process. Also getting the developer and activation solution to be exactly balanced so that it exhausts just enough to give good dmin on the positive image, but also just active enough to give good dmax on the positive image, is definitely not a trivial task. But as you can also see from the picture attached, the concept has legs, even if very weak ones.

Raghu Kuvempunagar · Jul 18, 2020

earlz said:
It's far from a trivial process, but yesterday I made "direct positive" prints by using fairly common developer chemicals and nothing else.

Very interesting work!

Is the main idea this: developer exhausts fast in the heavily exposed regions of the negative sheet and hence corresponding regions in the mating positive sheet will be proportionately less developed resulting in a positive image?

grainyvision · Jul 18, 2020

Raghu Kuvempunagar said:
Very interesting work!

Is the main idea this: developer exhausts fast in the heavily exposed regions of the negative sheet and hence corresponding regions in the mating positive sheet will be proportionately less developed resulting in a positive image?

Yes, that's exactly the idea. The Kodak patent method used really strange silver salts like silver mercapto and others that when developed would release an extremely strong inhibitor. Thus, the process they used relied on inhibition to form the positive image, rather than developer exhaustion. I assume this makes things significantly more stable, but we don't have access to such rare silver salts, not to mention making even a basic emulsion is out of reach or just too time consuming for most people.

The only idea I have to work on the inhibition rather than exhaustion concept is to develop the negative paper image normally, then use a rehalogenating bleach which forms silver iodide on the negative image. And re-developing it with the positive sandwich method so that it releases a lot of iodide in the strongly developed areas. The negative paper can then of course be rebleached and used over and over. Doesn't solve the contact problems, and I'm not sure even iodide is strong enough for this purpose

Donald Qualls · Jul 18, 2020

Nice -- that's an interesting alternative to using a foggant-doped gelatin receptor to catch and fog/develop halide migrating from the negative emulsion as you develop with a monobath (i.e. the 1940s Polaroid process, partly based on invalidated 1930s Agfa patents).

Raghu Kuvempunagar · Jul 18, 2020

@earlz: if you are going to first develop the negative sheet normally then would the method be technically a direct positive method? And isn't it much simpler to simply contact print from the resulting paper negative?

grainyvision · Jul 18, 2020

Raghu Kuvempunagar said:
@earlz: if you are going to first develop the negative sheet normally then would the method be technically a direct positive method? And isn't it much simpler to simply contact print from the resulting paper negative?

I tried it in every orientation and the best results were from developer on the fogged sheet and activator on the image sheet. It might just be that with the chemistry I'm using the alkaline exhaust before the developing agents

hvfrancesco · Jul 23, 2020

I've been experimenting a new bleach process, no need of sulfuric acid at all, it uses citric acid and sodium periodate. Sodium periodate is normally used as a screen reclaiming agent in screen-printing to remove old photo emulsion from screens.
So far I've tested on negative paper reversal, and the process is very effective and fast: complete bleach is reached in ten to twenty seconds.
Sodium periodate could be possibly a viable alternative to potassium permanganate process. It has some potential toxicity but it's used in rather low dilution and it allows a fast bleach without strong acid. Still experimenting.

Donald Qualls · Jul 23, 2020

hvfrancesco said:
I've been experimenting a new bleach process, no need of sulfuric acid at all, it uses citric acid and sodium periodate. Sodium periodate is normally used as a screen reclaiming agent in screen-printing to remove old photo emulsion from screens.
So far I've tested on negative paper reversal, and the process is very effective and fast: complete bleach is reached in ten to twenty seconds.
Sodium periodate could be possibly a viable alternative to potassium permanganate process. It has some potential toxicity but it's used in rather low dilution and it allows a fast bleach without strong acid. Still experimenting.

Does this bleach directly dissolve the silver the way permanganate/sulfuric, dichromate/sulfuric, or peroxide/(citric or acetic) bleaches do, or does it rehalogenate like ferricyanide or EDTA? I presume the former, if it's useful for reversal on paper negatives. Also, is this stuff going to get us on a "list" because it's a strong oxidizer like perchlorates? For that matter, would a perchlorate work as well (likely cheaper, if you buy it from a fireworks supplier)?

Raghu Kuvempunagar · Jul 23, 2020

Donald Qualls said:
Does this bleach directly dissolve the silver the way permanganate/sulfuric, dichromate/sulfuric, or peroxide/(citric or acetic) bleaches do, or does it rehalogenate like ferricyanide or EDTA?

@Donald Qualls: This patent could be of interest to you. The composition of the bleach is given in page 13. Also see an alternative composition in page 37.

"A typical photographic bleaching composition contains an oxidant (that is, a bleaching agent), an agent to retain oxidized silver in the element being bleached (usually a halide ion), and a buffer. In bleaching compositions based on complexed high valent metal ions, persulfate or peroxide, a separate agent is needed to accomplish each of these functions. One advantage of the present invention is that periodate bleaching agents can simultaneously act as an oxidant (bleaching agent), silver retaining agent (rehalogenating agent) and buffer."

Donald Qualls · Jul 24, 2020

Raghu Kuvempunagar said:
@Donald Qualls:"One advantage of the present invention is that periodate bleaching agents can simultaneously act as an oxidant (bleaching agent), silver retaining agent (rehalogenating agent) and buffer."

So, not a silver remover, then, but a rehalogenating agent. Silver chloride is soluble in ammonium hydroxide -- allowing removal of silver bleached with a chloride-bearing oxidant. Silver iodide, however, is hard to even fix. How does this contribute to reversal (paper or film)?

Raghu Kuvempunagar · Jul 24, 2020

Donald Qualls said:
So, not a silver remover, then, but a rehalogenating agent. Silver chloride is soluble in ammonium hydroxide -- allowing removal of silver bleached with a chloride-bearing oxidant. Silver iodide, however, is hard to even fix. How does this contribute to reversal (paper or film)?

It does. Silver iodide is very slow to develop and this can be leveraged in reversal. See this post for more information.

Donald Qualls · Jul 24, 2020

Okay. Then there's the issue that the first pricing I found for sodium periodide was about $39 for 5 grams...

Raghu Kuvempunagar · Jul 24, 2020

Donald Qualls said:
Okay. Then there's the issue that the first pricing I found for sodium periodide was about $39 for 5 grams...

Yes, it's expensive. Further, fixer might get exhausted faster because of silver iodide.

Donald Qualls · Jul 24, 2020

Hence asking about whether a perchlorate would work. Potassium perchlorate is fairly easy to come by from at least one fireworks supplier (yet, hazmat shipping, but common purchase quantity is in pounds), and the resulting silver chloride could be removed with an ammonia bath, as with other rehalogenating bleaches using a chloride donor.

Raghu Kuvempunagar · Jul 24, 2020

Donald Qualls said:
Hence asking about whether a perchlorate would work. Potassium perchlorate is fairly easy to come by from at least one fireworks supplier (yet, hazmat shipping, but common purchase quantity is in pounds), and the resulting silver chloride could be removed with an ammonia bath, as with other rehalogenating bleaches using a chloride donor.

To be fair to the periodate bleach patent that I shared, they do have a composition of the bleach that uses chloride along with periodate. In such a bleach, chloride acts as the rehalogenating agent while periodate acts as the bleaching agent. When such a bleach is used in reversal processing, it should be possible to use 2% ammonia solution to remove the rehalogenated negative image. Bleaching this way could actually be faster than bleaching with copper sulphate. And as no iodide is involved, fixing will also be faster.

However, @hvfrancesco isn't using chloride with periodate and is relying on periodate to be both rehalogenating and bleaching agent. Fixing will be longer due to the iodide.

Donald Qualls · Jul 24, 2020

I've seen bleaching done with crystal iodine and potassium iodide, leaving silver iodide. It's fairly fast and doesn't require anything expensive or excessively hazardous, but doesn't lend itself much to reversal because there isn't a good way to remove the iodide and leave the chloro-bromide we need for the next steps.

Obviously, this wouldn't be safe with bromide/bromine, much less chloride/chlorine, but it might lend itself to the "slow development" cited above (though that, to me, looks like you'll get muddy highlights).

General Treegan · Nov 18, 2023

My first test with the cerium sulfate formula. It works nice, I skipped the clearing bath which was not a good idea but the bleach works well, it is slow compared to copper but I prefer to no breath ammonia,

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