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  1. #1

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    Potassium Ferricyanide use

    To delete an area on a negative do I need to add in a de-foggant to potassium ferricyanide? I was going to mix it 1:20 and attempt to clear an area on a negative, but I am wondering if I would need to add some potassium bromide or some other de fogggant to make the area perfectly clear to print black.
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  2. #2
    Ian Grant's Avatar
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    You need to make a 10% solution of Potassium Ferricyanide and Potassium bromide, then dilute this to use as a bleach, when you've bleached the area wash & refix the negative. You will need to use a lot of care to ensure that the bleach doesn't ffect the rest of the image when you wash the negative.

    The other alternative is to use Farmers reducer which is similar but with Sodium Thiosulphate added, I prefer the first bleach because if you make a mistake you can wash & redevelop.

    Ian

  3. #3
    OMU
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    Quote Originally Posted by Ian Grant View Post
    You need to make a 10% solution of Potassium Ferricyanide and Potassium bromide, then dilute this to use as a bleach, when you've bleached the area wash & refix the negative.
    Ian
    Hi, a little different question, but do I have to refix after bleachin a paper too??
    Tanks :-)
    - OM

  4. #4
    Ian Grant's Avatar
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    Yes, because the bleach is re-halogenating the silver back to silver bromide, if you don't fix & wash it will slowly darken again.

    Ian

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    OMU
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    Thanks for your quick reply!! :-)
    - OM

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    If you are taking the paper back to base white in the areas you are removing the image, you may get yellowish staining with ferricyanide bleaches.

    If you do find this happening, the alternative would be to use an Iodine/Iodide bleach. I don't have access to the formulae at the moment, but if you want to know I shall post them when I get home.
    Steve

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  7. #7
    Ian Grant's Avatar
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    Steve, the Ilford formula is quite simple.

    IR-4 Iodine bleach

    Potassium Iodide 16 g
    Iodine 4 g
    Water to 1 litre

    To use mix 1+19 with water. After use re-fix in 20% plain hypo solution (Sodium Thiosulphate).

    I used this bleach extensively back in the late 70's & 80's, I found it often stained the emulsion and that a quick dip in developer before re-fixing completely eliminated the staining.

    Ian

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    Quote Originally Posted by Ian Grant View Post
    I used this bleach extensively back in the late 70's & 80's, I found it often stained the emulsion and that a quick dip in developer before re-fixing completely eliminated the staining.

    Ian
    Good tip. I've never had any problems with it myself, but it is good to know how to handle them if they crop up.
    Steve

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  9. #9

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    You need to make a 10% solution of Potassium Ferricyanide and Potassium bromide
    Please excuse my lack of chemistry knowledge, but what would this mean in terms of grams of each that I'd need to add to a liter of water?

  10. #10
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    A 10% solution is 100g in 1 litre (1000ml).

    Ian

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