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  1. #1
    mario Ag+'s Avatar
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    Potassium ferricynide question.

    Hi all,
    Is it posible to use Pot Ferricynide on it's own (without Pot bromide ) as a print bleach. I'm thinking of making a 10% solution first and highly diluting it to give me more control. Will this work? or is Pot Bromide esential in print bleach.
    Mario.

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    Ole
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    The bromide is only necessary if you are going to redevelop (i.e. tone) the print. Potassium ferricyanide will bleach on its own, but you should add either a halide (chloride, bromide or iodide) or thiosulfate (fixer) to take care of the released silver.
    -- Ole Tjugen, Luddite Elitist
    Norway

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    Les McLean's Avatar
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    Quote Originally Posted by mario Ag+ View Post
    Hi all,
    Is it posible to use Pot Ferricynide on it's own (without Pot bromide ) as a print bleach. I'm thinking of making a 10% solution first and highly diluting it to give me more control. Will this work? or is Pot Bromide esential in print bleach.
    Mario.
    If you are wishing to bleach the print to lighten highlights add a small amount of hypo crystals or ordinary fixer to the ferri solution. Ferri mixed with bromide is used to bleach the image and redevelope in toning solution when sepia toning.
    "Digital circuits are made from analogue parts"
    Fourtune Cookie-Brooklyn May 2006

    Website: www.lesmcleanphotography.com

  4. #4
    KenM's Avatar
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    Yes, you can bleach just using Pot-F. However, it's very important that you return the print to the fix to completely neutralize the bleach. I don't like adding fix to the bleach, since it drastically shortens the life of the bleach (yeah, yeah, it's cheap, I know).

    Also, keep in mind that some papers (Ilford, to name one) may not bleach very easily unless you add some fix to the bleach to help things along. Forte papers bleach very easily with just bleach....
    Cheers!

    -klm.

  5. #5
    mario Ag+'s Avatar
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    Thank you all for your replies.
    Mario.

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    Quote Originally Posted by mario Ag+ View Post
    ...or is Pot Bromide esential in print bleach. Mario.
    P. ferricyanide oxidizes elemental silver. The oxidized
    silver will complex with fixer and be removed. If bromide
    is present the oxidized silver is converted on site into
    silver bromide. So with bromide present the image is
    left as silver bromide.

    Now what would happen to that remaining image if it
    were exposed to light and put through a print developer.
    Anybody tried that? And to make it more interesting,
    if it were a chloro-bromide paper at start,
    at end it is a bromide only. Dan

  7. #7

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    Quote Originally Posted by dancqu View Post
    P. ferricyanide oxidizes elemental silver. The oxidized
    silver will complex with fixer and be removed. If bromide
    is present the oxidized silver is converted on site into
    silver bromide. So with bromide present the image is
    left as silver bromide.

    Now what would happen to that remaining image if it
    were exposed to light and put through a print developer.
    Anybody tried that? And to make it more interesting,
    if it were a chloro-bromide paper at start,
    at end it is a bromide only. Dan
    If you fix after ferri-bromide (or mix of halides) the silver halides will be removed. If you don't fix, they can be redeveloped. I use this a lot and we usually have a whole day of 'bleach and redevelopment games' on my longer workshops. It's not only great fun but very useful and can be creative.
    It gives you the chance to bring a print back in a warmer or colder tone, higher or lower contrast or in lith developer as wel as in a variety of toners.
    Yes, changing the halides does change the results.
    Tim

  8. #8

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    Quote Originally Posted by tim rudman View Post
    It gives you the chance to bring a print back...
    Yes, changing the halides does change the results. Tim
    I'd suppose the halide or mix thereof would affect
    the amount of post ferricyanide exposure needed?

    After rehalogenation and the correct amount of
    re-exposure does a same print developer
    reproduce same results? Dan

  9. #9

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    Quote Originally Posted by dancqu View Post
    I'd suppose the halide or mix thereof would affect
    the amount of post ferricyanide exposure needed?

    After rehalogenation and the correct amount of
    re-exposure does a same print developer
    reproduce same results? Dan
    You are right that different halides might require different exposures - but the exposure is all done at the first exposure. There is no need to re-expose after bleaching. The bleaching and redevelopment are all done in normal room light, not safe light.
    The idea is as follows:
    1) You buy a sheet (packet/box etc) of paper coated with a (light sensitive) silver halide all over.
    2) You expose through a neg to produce a latent (invisible) image
    3) You develop the paper to change the silver halide THAT HAS BEEN EXPOSED TO LIGHT into metallic (visible) silver - the image.
    4) at this point, you can't turn on the lights as all the original (non image) light-sensitive silver halide(s) is still present all over the paper and would react to light
    5) You fix the print. This removes all the unexposed silver halide, leaving only the metalic silver of the image. White areas have no silver (halide) left at all if you fix fully. You can now put lights on.
    6) you now wash to remove fixer AND silver/fixer complexes (argentothiosulphates)

    Now you have a halide-free print with an image made of silver metal, which (unlike the silver halide) is visible.

    If you bleach this silver image in a Pot. Ferri/halide bleach (e.g. a sepia kit bleach) you convert this metallic silver back into a silver halide.

    This is where we began - ALMOST
    But the silver halide we now have is
    a) only where the image was - not all over the paper, and
    b) is less light sensitive and can be handled in normal room light reasonably well.

    SO - we can go back to the beginning and develop again. The image is there so no further exposure is needed.
    BUT - this 2nd development can be in a different developer - e.g. cold tone, warm tone, Lith, high contrast, low contrast etc etc etc, ... so you see how useful and powerful this can be ...

    but there's more ;-) ...

    - The bleach can be full or partial (leaving part of the image unaffected)
    - The bleach can contain different halides, or mixes of halides
    - The 2nd development can be complete
    - Or it can be partial (different colours from partly developed grains - especially good with Lith dev)

    If the 2nd dev is partial the print will become lighter in the 2nd fix (you must re-fix if 2nd dev incomplete as silver halides still exist that haven't been developed back to silver metal and these are unstable in light eventually)
    SO - you may ned to compensate for this by making the original print a bit darker.

    The point of all this is that
    - you can now not only have all grades in one box of VC papers, you can have many different paper types as well! How cool is that!?
    - You can also make '2nd pass' Lith prints that are quite different.
    - You can also change the way a certain paper responds to selenium (for example) toner - WOW ;-))
    and - as they say - so much more ;-)

    That is the basis of part of my 'Day at the Bleach' worshop day - or if you prefer .. 'Once more into the Bleach dear friends'
    Tim

  10. #10
    AgCl4ever's Avatar
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    [QUOTE=mario Ag+;396191]
    Potasium Ferrocyanide by itself can be applied to the to-be-lightened area of the print and seems to do nothing... but, when the area is flushed with/ placed in hypo the dark silver is lightened/ removed/ bleached. If K Ferrocyanide is mixed with hypo you get Farmer's Reducer which bleaches in a visible way, you can see it work - you still should refix.

    Some of the (few remaining B&W) pro labs bleach by using K ferricyanide on a brush, and rinsing with hypo which is circulated through a small hose.

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