Looking for a formula for rehal bleach (recovering C-41 in black and white)

[pwadoc]

Hello all, so I accidentally managed to get a C-41 roll mixed in with my black and white film and ran it through the Jobo. I've been reading that it's possible to use a re-halogenating bleach to re-silver the film and then redevelop, but I'm not quite clear on what sort of bleach would qualify. Just to be clear, this is just an experiment, I'm going to scan the roll as-is regardless, I'm just interested in what effect re-development will have.

I currently have on hand a bunch of Flexicolor Bleach III, but from what I'm read it's not what I need. I also have some powdered Potassium Ferricyanide, and a formula from the Darkroom Cookbook for a print rehal bleach requiring Potassium Ferricyanide and Potassium Bromide. I've read some accounts that indicate I can make a rehal bleach with the Potassium Ferricyanide alone. Can anyone help clarify the best way for about getting or mixing some rehal bleach to test this process? Thanks!

 

[Anon Ymous]

The Flexicolor bleach is a rehallogenating one, so it should do the trick just fine.

 

[Rudeofus]

Flexicolor Bleach III contains ammonium ions, there's a non-trivial chance that it will remove some silver. Even if it deposits that silver elsewhere it would create issues.

Most popular rehal bleaches are based on Potassium Ferricyanide and Potassium Bromide. Typical recipes use 10-50 g of each in 1000ml water.

 

[Doremus Scudder]

If you've developed and fixed your film, there's no silver left to rehalogenate except the image silver. If you bleach/rehalogenate that, the color-coupling dyes are surely gone. You could only redevelop it as black-and-white film. What is that you are trying to do?

Doremus

 

[Rudeofus]

Where would the color couplers go? They are well mordated to stay in the emulsion, or you'd have very freaky results within a few minutes of color development.

The C -41 procedure B&W developer/fixer/wash/rehal bleach/wash/reexpose/color develop/bleach&fix/wash is known to work, so I expect few issues with it apart from some limited image degradation.

 

[cowanw]

What happened to the colour couplers interested me so I looked around and found these two bits of information
en.wikipedia.org/wiki/Cross_processing
Other interesting effects can be obtained by bleaching color films processed in black and white chemistry using an hydrochloric acid dichromate mixture or using potassium triiodide (KI3) solution. If these bleached films are then re-exposed to light and re-processed in their intended color chemistry, subtle, relatively low contrast, pastel effects are obtained."


And a quote from 2005

You can convert a B/W processed C-41 film back into a colour neg film.
It is a bit long-winded and the colour reproduction is not exactly the
same as it would have been, but it would solve (most of) your problems.
The negs would still benefit from scanning.

We used to charge £15 per roll for this type of recovery, but I have
not done it for a while. If you are interested, drop us a line - we
can always do a clip test for you to see if it works well enough on
your film (I didn't see what film brand you were using - some behave
differently to others due to the anti-halation layer techniques used)
I will have to get some samples of this sort of thing on the website
when it reappears.

Dominic Roberts
'Process C-22'
England

email - info 'at' processc22.co.uk
http://www.processc22.co.uk

 

[Doremus Scudder]

Rudi and Bill,

I stand corrected! I erroneously assumed that the dye couplers not used in image making ended up being somehow made soluble and washed away, even when C41 gets processed as black-and-white. The opposite appears to be true, which I find fascinating.

Best,

Doremus

 

[Photo Engineer]

Do NOT use the C41 Bleach. It will virtually ruin the image.

Use a true rehal bleach with Ferricyanide and Bromide. Use it for about 5 minutes at 100F, then wash 5 minutes at 100F, then run a normal C41 process. The image will not be good but it will be better than B&W, and you can always print it as B&W and get a reasonable image. A bleach bypass might be good too, where you don't bleach or fix, just dev, stop, wash, final rinse and then dry. This image can be interesting as well.

PE

 

[Photo Engineer]

As a side note, I would not recommend KI3 as if forms AgI which is very difficult to develop and when/if it does, the image may be severely distorted due to adjacency effects.

PE