Working B&W reversal process with ferricyanide bleach

[River Mantis]

I haven't seen any notion of this process in literature but some photo chemist told me that he had read about it once. So I kind of reinvented it. The idea is simple: just use a toner right after the first development. It turns undeveloped silver halide directly into highly stable silver sulfide which allows you to use a rehalogenating bleach like in color processes. This way you are avoiding using of strong oxidising bleaches. Dichromate is not just toxic but it can be hard to obtain in some countries. The permanganate bleach in turn is prone to emulsion damage. I personally had success with it only if the stinky formaldehyde pre-hardening bath was involved.

Step	Time at 20ºC, min
First Developer	Depends on film and chemistry, for low ISO films and D-67 developer it's 7 min
Wash	5
Toner (see below)	1
Wash	5
Bleach (see below)	5 (?)
Wash	5
Acid Fixer	10
Wash	5

The toner is 1% thiourea solution in 2% sodium hydroxide solution (Haist)

The bleach is a modified ECN-2 "alternative" bleach aka SR-29

Water	900 mL
Potassium Ferricyanide anhydrous	40 g
*or Potassium Ferricyanide trihydrate	47 g
Sodium Bromide anhydrous	25 g
*or Potassium Bromide	30 g
Water to make	1 L

Possible improvements:
As the toner is not meant to be stored it's concentration can likely be lowered for one-shot use.
The number of baths can be reduced to just three if blix is used.

Some sample images:

Update:
I found at least one related post: https://www.photrio.com/forum/threa...essing-using-sepia-toner.155754/#post-2018742
Also this: https://www.35mmc.com/02/07/2022/ma...ner-kit-by-andrew-smale/?utm_content=cmp-true
And the earliest mention I could find, dated back to early 2000s: http://www.profotos.com/education/promag/articles/monotrans/index.shtml

 

[DeletedAcct1]

That's a clever and very interesting way of obtaining slides. The sepia tone adds some uniqueness to it.
I was wondering which film you used and if you've got any sort of emulsion damage (actually it's not the emulsion that fails but the subbing layer - but let's refer to it as emulsion damage).

 

[River Mantis]

That's a clever and very interesting way of obtaining slides. The sepia tone adds some uniqueness to it.
I was wondering which film you used and if you've got any sort of emulsion damage (actually it's not the emulsion that fails but the subbing layer - but let's refer to it as emulsion damage).

I used cheap Fomapan 100 for tests. And I see no damage at all. The toner is highly caustic but also very active and one minute is not enough to cause damage.

 

[khh]

That's a very interesting process. Could you use C41 bleach or RA4 Blix with this process, do you think? I might have to try.

 

[koraks]

Smart!

Could you use C41 bleach or RA4 Blix with this process, do you think?

I'd expect so, yes. Neither should affect silver sulfide, but will remove the unwanted silver negative.

 

[River Mantis]

That's a very interesting process. Could you use C41 bleach or RA4 Blix with this process, do you think? I might have to try.

I'm pretty sure you can use C41 bleach or blix

 

[lamerko]

This is very interesting and I will give it a try. But wasn't thiourea a strong fogging agent?

 

[DeletedAcct1]

I'm pretty sure you can use C41 bleach or blix

bleach yes, blix no I suppose...

 

[River Mantis]

bleach yes, blix no I suppose...

I see no reason why blix may not work. Also I added a link below to the small note made by a guy who did exactly that

 

[River Mantis]

This is very interesting and I will give it a try. But wasn't thiourea a strong fogging agent?

It can be if you put an undeveloped film in contact with it (in its pure form)

 

[lamerko]

It can be if you put an undeveloped film in contact with it (in its pure form)

My thought was that one must be very careful not to contaminate the room with this chemical...

 

[koraks]

But wasn't thiourea a strong fogging agent?

Yup. That's why it works so well here. It totally fogs the undeveloped silver halide, leaving the silver negative image unaffected.

My thought was that one must be very careful not to contaminate the room with this chemical...

There's some wildly overblown warnings about this online. I've used thiourea in several applications in my darkroom for years, and not just once or twice, but regularly. Not a single unintended fogging event noticed to date, ever.

 

[lamerko]

There's some wildly overblown warnings about this online. I've used thiourea in several applications in my darkroom for years, and not just once or twice, but regularly. Not a single unintended fogging event noticed to date, ever.

Thanks. I have always been wary of this chemical because of these warnings. But on the other hand, I have dichromate, which is certainly worse in all situations...

 

[koraks]

Dichromate doesn't fog silver halides. Of course it carries other risks.
The alleged risk of handling thiourea in a darkroom is often overstated. I'm not quite sure why this is the case. It may because people confuse it with sodium sulfide, which has a tendency to release hydrogen sulfide vapors, which will fog silver halide emulsions. Thiourea doesn't do this.
Thiourea is a suspect carcinogen, so it's not necessarily benign, but it's not a concern unless you manage to ingest it. As with all photo chemistry, evidently take precautions against this. With thiourea, these precautions don't have to be particularly draconian.

 

[MattKing]

Not a single unintended fogging event noticed to date, ever.

I assume that at least, not a chemical one

 

[koraks]

Well, I'm not in London, hehe!