Bleach without colour shift

Discussion in 'B&W: Film, Paper, Chemistry' started by Jarvman, Oct 20, 2012.

  1. Jarvman

    Jarvman Member

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    Oi oi. A quick one.

    I want to locally bleach a print with a cotton ball. However, I am aware that pot ferri. bleach shifts the tone of a print to a warmer colour. Is there any way to bleach back a print without making a noticeable shift in colour?

    Cheers,
    Gareth
     
  2. BMbikerider

    BMbikerider Member

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    It is a long time since I beached or reduced the tone of a print usin pot ferri. I seem to remember that to bring the original colour back you had to re-fix the print. Don't take my word for it, try it on an old print first.
     
  3. artonpaper

    artonpaper Subscriber

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    I take a mall amount of potassium ferricyanide like a 1/4 -1/2 teaspoon in maybe two oz of water. then I add an equal amount of fixer, working strength to the bleach. It bleaches and fixes at the same time. The effects are not reversible and I've never had a color shift. There are some very complex bleach formulas out there. if you're interested I will look around for the formulas I've collected.
     
  4. Blighty

    Blighty Subscriber

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    From 'Rayco reveals'. Non-staining reducer as follows. Solution A Thiourea 8g; sodium thiosulphate (anh) 220g; water to make 1 litre. Solution B potassium Ferricyanide 38g; water to make 250ml.
    For use, mix 5 parts of A, 14 parts of water and 1 part of B. This is my standard bleach and I've used it on several different papers. It does not stain and works pretty quickly although it does exhaust very quickly.
     
  5. jordanstarr

    jordanstarr Member

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    ...it doesn't warm. The bleach is yellowish if you're using pot ferri. After each bleaching application it needs to go back into the fixer for 1 minutes to take the bleach out, then go again. After you're done, wash for 25-45 min and then it will go back to normal.
     
  6. chimneyfinder

    chimneyfinder Member

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    Just be very patient with the process, don't try to get it in one hit and mix as artonpaper suggests or use a readily available Farmers Reducer. Look up articles by Tim Rudman, for example, or get one of his books for a real practical approach on bleaching and toning. You shouldn't get a noticeable colour stain if you have the print on a sloping board with a hose or jug of water handy to wash each application of bleaching (Preferably with the wash water running into dark areas rather than light, as lght tones would be most noticeably affected).
    I am also doing some local bleaching at the moment and not getting staining, but approach with care and do it with a good light on the piece.
    Regards, Mark Walker.
     
  7. Doremus Scudder

    Doremus Scudder Member

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    I do quite a bit of bleaching using a potassium ferrocyanide/potassium bromide rehalogenating bleach.

    My experience is that, unless the bleaching is severe, most papers do not change appreciably in image tone if you proceed carefully. The same goes for when I used ferricyanide alone or with fixer added (Farmer's Reducer).

    You do have to re-fix and wash adequately regardless of the bleaching procedure you use.

    In case you are interested, here is my procedure:

    Note: this technique turns silver into “invisible” silver bromide that needs to be fixed away. However, you can redevelop (to a certain extent) if you bleach too far by simply returning the print to the developer before the fixing step. However, since the halides formed by the bleach are different from the original, there can be a change in image tone of the bleached/redeveloped area. Sometimes it is just fine, sometimes it is different enough to ruin a print. It depends on how much redeveloping you do and the original composition of the paper.

    For local bleaching, I prepare a dilute ferricyanide/bromide solution of about 2% by adding 10 drops of 10% ferricyanide solution and 30 drops of 3.2% potassium bromide solution (I have these on hand always) to 10ml water, or equivalent for larger batches. (You can mix the appropriate dilution in larger quantity for overall bleaching, basic solution is 1g pot. ferricyanide and 1g pot. bromide / liter). This solution is a starting point and can be strengthened or weakened as needed. You can keep the solution until it changes color to green from the original yellow. Life is shortened if the solution is contaminated by fix.

    I use everything from Q-Tips to Japanese calligraphy brushes for local bleaching, sometimes even a paper towel dampened in the bleach. I like to work very slowly. I slap the print to be bleached onto the back of a tray that has been propped in the sink, so it is at an angle. With bleach in one hand and water hose in the other, I apply bleach to the area I want while keeping the water trained on the print just underneath that area to prevent streaking.

    A bit of bleaching, then a rinse, then 30 seconds or so in the fixer, then another rinse in a tray of running water; repeat as needed to gradually get the effect you are looking for.

    I find that with the rehalogenating bleach, the bleaching slows down after a couple of applications if you don't fix out the rehalogenated silver. That said, make sure that you haven't overdone it before the fix step.

    That's a "nutshell" explanation of what I do, but bleaching is really an art. I find that I can minimize changes in image tone by going slowly and making sure not to tone too much later (often, the bleached areas will tone differently). And, as I said, some papers are better than others in this regard.

    Have fun,

    Doremus


    www.DoremusScudder.com
     
  8. newcan1

    newcan1 Subscriber

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    I've been trying very weak ferri bleach to bleach back papers that have a bit of base fog. I have found that it does render a neutral of cold black somewhat warmer/muddier. Very weak solution seems better.

    Has anyone tried iron EDTA bleach, such as RA4 bleach, for bleaching b&w paper? I may give this a try this week