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  1. #1
    polyglot's Avatar
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    Bleach & colour processes

    Hi all,

    I've done a bit of reading (and searching on APUG) wrt Bleach Bypass. Clearly one can bypass the bleach stage altogether which will result in serious contrast, but what surprises me is that people recommend underexposing by a stop in order to bring some of the highlights back, presumably in favour of lost shadows. Surely it would be a much better approach to pull the film by a stop, i.e. overexpose and then underdevelop the film? That way, you ought to be able to get less-crazy contrast while still having the desaturated look.

    So, any suggestions on first-dev times to try for a pull?

    As for re-development, can someone please explain the technical difference between rehal and non-rehal bleaches? As I understand it, a rehal bleach will make the emulsion light-sensitive again whereas a non-rehal will not, therefore E-6 uses a rehal bleach in order to perform reversal fogging, correct? And C-41 uses a non-rehal bleach just to "un-develop" all the silver before fixing it all out.

    The bit I care about: assuming I apply a non-rehal (C-41) bleach to completion, I can then re-develop the latent image directly afterwards, can't I? Or must it be a rehal bleach to get that behaviour? I intend to do colour-dev, bleach, rodinal, fix to get a partial bleach-bypass look.

    Any suggestions on times for Rodinal, D76 or XTOL for redeveloping C-41 negs?

    thanks...

  2. #2
    Athiril's Avatar
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    reversal fogging occurs before the bleach in E-6.

    Non-rehal bleach removes silver off the film, rehal bleach rehalogenates it back to silver halide.

    C-41 uses a rehalogenating bleach. B&W slides use a non-rehal bleach.


    You need a rehal bleach to redevelop.


    Rodinal will add a small amount of dye to colour film. There is also no point to the process above. Also the fix needs to be after colour dev, before bleach for re-developing. Otherwise you will just develop fog/flat silver, and will have to bleach and fix the silver off to show your colour image.

    You will just bleach back the silver developed b&w neg and re-develop it.. it wont change much, except you'll add a tiny bit more colour through Rodinal.

    Normally with re-developing you run C-41 again for more colour/gain.. or b&w dev first to set the tonality from a b&w developer, then fix, bleach, re-develop, bleach, fix, etc.


    colour developer (this case C-41) also reduces silver halide to silver, same as a b&w dev, you can dev b&w film with C-41 if you bleach bypass.





    What you want to try (from the concept of your idea) is running the C-41 shorter, ie: perhaps 2 minutes, then using a stop bath, rinse twice, and then use Rodinal, and then just fix, no bleach. Or Rodinal first, stop, rinse twice, short C-41, stop and rinse, fix. etc.


    That way (either of the last two examples) you can adjust C-41 time for more or less dye as you need it. And adjust Rodinal/b&w dev time/dilution for more or less b&w neg overlay as you need it (ie: if it's overall too dense or too thin).




    During my Rodinal re-developing C-41 attempts... 1+100 1 hour stand, and 1+25 (+~16g non-iodised table salt) for 8 minutes both developed C-41 to good density, I redeveloped them to full colour and completely removed the b&w portion of these images though:


    Little Cousin by athiril, on Flickr



    Now given C-41 @ 3m 15s @ it's processing temp gives good density for it's process.. it also develops silver, which is removed normally, so bleach bypassing will shoot up the density as you will have dye density + b&w silver density, so C-41 needs to be reduced, as does normal b&w processing time that gives good density for C-41 films.

    You may want to drop to 30 celsius, where the full C-41 processing time is arond 8 minutes (according to tetenal), so you can run 3 minutes or 2 minutes if you need to for 1/4 time for very small saturation.



    For super low saturation.. you may also be interested in just Rodinal by itself with a bleach bypass.



    Rodinal Colour Developer Test by athiril, on Flickr

    Exceptionally low.. you could try that... shorten the stand to 30 min, and just add 1-2 min of C-41 @ 30c after that, should give a little more colour. (it was quite dense at the 60 minute stand to begin with)
    Last edited by Athiril; 06-27-2011 at 07:54 PM. Click to view previous post history.

  3. #3
    polyglot's Avatar
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    Why does C-41 use rehal bleach, since by default there is no redevelopment? If it is though, that's fine for my purposes.

    Got some experimenting to do I think.

  4. #4
    Athiril's Avatar
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    Rehal Bleach converts silver to silver halide, Fixer removes silver halide. Bleach in E-6 also occurs after re-development anyway. That way nothing get's left behind.

    Non-rehal bleaches can do other things to the film.. esp permanganate bleaches.

  5. #5
    polyglot's Avatar
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    Is there a reference somewhere on the different classes of bleach, typical chems used in each type and the effects that each has in terms of what will happen with subsequent processing steps?

  6. #6

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    Potassium bichromate used in bw-reversal process can't be used with C41/E6 because destroy all color layer.

  7. #7
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    You should think it like this:

    1) Rehalogenating bleaches -- ALL of the silver is turned to silver halides. This is needed when the whole image is to be redeveloped. Example: Potassium ferricyanide + bromide.

    2) Typical color bleaches, often called non-rehal -- not all silver is turned to silved halides; some is removed directly. But these are still PARTIALLY rehalogenating! Example: Ammonium ferric(III) EDTA

    3) BW reversal bleach, which is completely non-rehalogenating. It attacks the emulsion quite a bit, is very acidic and more toxic and expensive and needs a clearing bath afterwards because it stains the emulsion, so there is no point in using it if the complete direct removal of silver is not needed. In BW reversal, this is a must because the existing halides are used to make the final positive image; if the bleach converted any silver to halides, they would mix together. Example: Sulfuric acid + permanganate or dichromate.

    In E6, all of the silver is removed anyway so there is not a mix-up problem -- dyes are only created in the second development. First one is non-dye creating developer (BW developer)

  8. #8
    polyglot's Avatar
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    thankyou hrst; that clears up a lot of confusion for me.

    I take it with the rehalogenating bleaches, the result is 'activated' (exposed) silver halides that can be reduced again to silver by developer, as opposed to unexposed halides that just sit there. Or does the film need to be exposed to light before being redeveloped?

  9. #9
    Athiril's Avatar
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    You can just re-develop, but it'll help quicken the process a bit to re-expose it. After all your first developing is done and stopped (ie: at the fix step) you can open the tank to light for the rest of it.

    In practise, I haven't had a problem using Flexicolor III and Agfa AP-70 bleaches for re-developing.

  10. #10
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    Most of what you guys are doing, I did about 40 years ago. Good luck!

    PE

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