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  1. #1
    Athiril's Avatar
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    Alternative B&W Bleaching Formulas/Methods

    Been working on this for a little while.

    Dichromate bleach is excellent and reliable. Of course people have concerns with it.

    Permanganate bleach is unreliable and damages film, but is much safer for you to handle. And as it reduces, MnO2 precipitates onto the surface of the film, and also inside of the gelatin. Emulsion can peel off as well.


    Anyway, one example, which worked well for me, ended up with a dMax of 2.12 of unexposed area (old base fogged film, so it's pretty good), was potassium permanganate (enough to get that 'opaque' look in solution) in 250g/L of citric acid.

    Silver Citrate isn't soluble in water, but it is in a good concentration of citric acid. Citric acid also keeps MnO2 from building up on or in the film. And it takes the edge of the permanganate bleach, so that it can be run at elevated temperatures and long times without damage.

    It is however one shot, as the citric acid slowly reduces the permanganate and eventually clears it completely.

    The time it took me to bleach a film with this was approx 16 minutes or so. I added some more potassium permanganate solution to it near the end (just a little) to finish it off.




    The other thing I have done is copper sulphate with sodium chloride. Followed by a 300g/L Ammonium Chloride bath to dissolve the silver chloride selectively. Bleaching was done quickly, but the clearing time in the ammonium chloride I used was 30 minutes, but it becomes hard to tell when to finish. Think I also had the absolute thinnest neg left over stacked on top of the positive, basically unnoticeable.

    But some of the silver bromide was also dissolved. dMax on the same film and developer process with this ended up being just 1.52 down from 2.12, but otherwise did work.

  2. #2

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    Permanganate bleach is unreliable and damages film, but is much safer for you to handle. And as it reduces, MnO2 precipitates onto the surface of the film, and also inside of the gelatin. Emulsion can peel off as well.
    Manganese dioxide should not form if the bleach is used properly. It is important that the bleach is acidic and then the permanganate will be reduced all the way to Mn+3.

    The only bleach that I have had trouble with is the copper one which caused severe softening and frilling of the emulsion
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  3. #3
    Athiril's Avatar
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    Quote Originally Posted by Gerald C Koch View Post
    Manganese dioxide should not form if the bleach is used properly. It is important that the bleach is acidic and then the permanganate will be reduced all the way to Mn+3.
    This happened in another test I was doing, it was certainly acidic, but it wasn't sulphuric acid, it was acetic acid.

    Quote Originally Posted by Gerald C Koch View Post
    The only bleach that I have had trouble with is the copper one which caused severe softening and frilling of the emulsion
    Haven't had that, have only ever had trouble with permanganate + bisulphate and sulphuric acid bleaches. I haven't tried the CuSO4 + H2SO4, as that seems unlikely to work.

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    When bleaching is stopped at the manganese dioxide point half the bleaching capacity of permanganate is lost.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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    Athiril's Avatar
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    The citric acid on it's own will reduce permanganate over time, it's not fast like sodium sulphite for example, but over the course of an hour or so.

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    You really must use sulfuric acid in the permanganate bleach. Acetic acid is not strong enough.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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    Never had a problem whatsoever when I began using permanganic acid at 18°C

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    Quote Originally Posted by Gerald C Koch View Post
    You really must use sulfuric acid in the permanganate bleach. Acetic acid is not strong enough.
    How about Sulfamic Acid? It is so much easier to handle than Sulfuric Acid ...
    Trying to be the best of whatever I am, even if what I am is no good.

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    Dear Athiril

    Well, at least the stability of the permanganate bleach can be improved easily.
    Add about 20g Calgon per liter and the result should be much better.

    Look for this agfa link for further explanation. www.google.com/patents/EP1006408A1?cl=en


    The final formulation will look this way. The text is quite promising, but I must admit that I haven’t used it till now…

    Water 700 ml
    M 19 (Natriumkaliumhexametaphosphat) 20 g
    Potassium permanganate 2 g
    Sulfuric acid (20 wt -%) 27 ml

    Fill with water to 1000 ml (pH = 1.4)


    In this movie forum is roughly the same formulation, just slightly different sulfuric acid concentration.
    http://movies.groups.yahoo.com/group...ng/message/891

    Regards Stefan

  10. #10
    Hexavalent's Avatar
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    Quote Originally Posted by Rudeofus View Post
    How about Sulfamic Acid? It is so much easier to handle than Sulfuric Acid ...
    Sulfamic acid will merrily dissolve silver; it might just do a little more bleaching than desired.
    - Ian

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