Bleach composition question

[Anon Ymous]

Hello all,

lately I got interested in toning and as a result I started searching for information about it. I'd like to try sepia toning and it seems (from what I've read so far) that indirect toning gives stronger results. Moreover, warmtone papers are said to be more up to the task. So, it seems that chlorobromide emulsions are more receptive. I've got some questions and I'd be grateful if you could tell me if I'm wrong or right. (Or probably where I'm wrong)

1. The various bleach formulae have a rehalogenating effect. I assume that the metallic silver left on the paper becomes silver halide, just like it was before being developed*. As far as I can tell (from my web searches), all bleaches are made of potassium ferricyanide and potassium bromide. I guess it means that bleaching turns silver to silver bromide.

2. If 1 is correct, then using a different potassium salt could give a different halide. Why not use potassium chloride, or a KBr/KCl combination? Wouldn't that make a difference regarding the final image tone?

That should (in effect) make a bromide paper chloride/clorobromide, but I guess I'm wrong somewhere. After all, toning must be the result of the following reaction:

2AgX + Na2S -> Ag2S + 2NaX

But that would make the actual halogen irrelevant.
Comments anyone?

* Hence the safelight warning I've seen when doing it.

 

[snallan]

Hi Anon Ymous, the ferri bleaches using pot bromide as rehalogenating agent are the most common.

However, you can substitute other halide salts or combinations of them, and it can have a significant effect on the colour achieved. In fact you do not have to use a ferri/halide bleach. You can check out a couple of samples I posted on this thread (there was a url link here which no longer exists), these are using a ferri/bromide bleach, a ferri/chloride bleach, and a cupric sulphate bleach.

Lighting for bleach/tone operations can be pretty bright, I generally do it under normal room light. Though I stay away from fluorescent light, or bright daylight. As the UV content of both could cause premature printing out of the bleached image.

 

[Anon Ymous]

Interesting thread Steve, thanks a lot!

 

[dancqu]

I guess it means that bleaching turns silver to silver bromide.
...........................................................................
But that would make the actual halogen irrelevant.
Comments anyone?

Ferricyanide is a strong oxidizer and converts elemental
silver into silver ferrocyanide. Silver ferrocyanide is very
insoluble; the image stays in place. In the presence of
an even more insoluble salt the silver is converted
into that least soluble salt.

Although no one claims to have tried it I see no reason,
other than end results, to not tone after bleaching.
That is, tone the ferrocyanide image. Or, for
that matter, expose and redevelop.

According to Mr. Rudman bleaching can precede
the conversion of the silver ferrocyanide image.
The halogens are not the only highly
insoluble salts of silver. Dan