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Thread: Trying out Chromium intensifier

  1. #11

    Join Date
    Jul 2010
    Location
    Singapore
    Posts
    217

    Re: Trying out Chromium intensifier

    thanks for all the good advice.
    Safety is always number 1 when handling chemicals even more when dealing with dichromate and hydrochloric acid.

    freestyle is selling a powder kit too here https://www.freestylephoto.biz/05006...Powder-1-Liter
    Looking at the MSDS, it seems to be have potassium dichromate and sodium bisulfate which make it sulphuric acid based rather than using hydrochloric acid.

  2. #12

    Re: Trying out Chromium intensifier

    Quote Originally Posted by pound View Post
    freestyle is selling a powder kit too here https://www.freestylephoto.biz/05006...Powder-1-Liter
    Looking at the MSDS, it seems to be have potassium dichromate and sodium bisulfate which make it sulphuric acid based rather than using hydrochloric acid.
    For the bleach to work as an intensifier, it needs to be rehalogenating - i.e. it should convert all silver to silver halide which can be redeveloped subsequently. This is the reason why hydrochloric acid is used in chromium intensifier as it supplies Cl- ions needed for rehalogenation of the silver by chromium and provides the pH needed for the bleach to work. If sulphuric acid (or bisulphate) is used in place of HCl, the bleach is no longer a rehalogenating bleach. All the silver will be converted by such a bleach to silver sulphate which dissolves in water. This is the bleach we use regularly in B&W reversal to remove the negative image. Maybe Formulary's intensifier also has sodium chloride which is not listed in MSDS as it's not hazardous.

    If you're mixing chromium intensifier yourself from dichromate without wanting to deal with hydrochloric acid, you can try this formula that I have used successfully for intensification of b&w slides:

    Water: 800ml
    dichromate: 10g
    glacial acetic acid: 50ml
    sodium chloride: 20g
    water to make: 1000ml

    You can replace glacial acetic acid by lower concentration variety with appropriate changes to volume used.

  3. #13

    Join Date
    Jun 2013
    Posts
    157

    Re: Trying out Chromium intensifier

    Interesting, thank you. A question: with regular chromium bleach, the degree of intensification is adjusted with the dilution of HCl, somewhere between 0.5% and 1% from "pure" HCl; less HCl for more intensification. With your alternative formulation, should one adjust NaCl (my bet) or acetic acid?

  4. #14

    Join Date
    Jul 2010
    Location
    Singapore
    Posts
    217

    Re: Trying out Chromium intensifier

    Quote Originally Posted by Raghu Kuvempunagar View Post
    ...Maybe Formulary's intensifier also has sodium chloride which is not listed in MSDS as it's not hazardous.
    ....
    If you're mixing chromium intensifier yourself from dichromate without wanting to deal with hydrochloric acid, you can try this formula that I have used successfully for intensification of b&w slides:

    Water: 800ml
    dichromate: 10g
    glacial acetic acid: 50ml
    sodium chloride: 20g
    water to make: 1000ml

    You can replace glacial acetic acid by lower concentration variety with appropriate changes to volume used.
    Good information. Indeed there is sodium chloride listed in the Formulary's intensifier MSDS too. I look around the Darkroom Cookbook book but did not find a intensifier formula listed using this 3 ingredients.

    Thank you for yr other formula. Looks like I can try household vinegar (5% acetic acid) in place of GAA as that is also hard for me to get hold off.

  5. #15

    Re: Trying out Chromium intensifier

    Quote Originally Posted by pound View Post
    Thank you for yr other formula. Looks like I can try household vinegar (5% acetic acid) in place of GAA as that is also hard for me to get hold off.
    As long as it is pure 5% acetic acid, it should work.

  6. #16

    Re: Trying out Chromium intensifier

    Quote Originally Posted by Bernard_L View Post
    Interesting, thank you. A question: with regular chromium bleach, the degree of intensification is adjusted with the dilution of HCl, somewhere between 0.5% and 1% from "pure" HCl; less HCl for more intensification. With your alternative formulation, should one adjust NaCl (my bet) or acetic acid?
    Chromium intensifier works by forming a chromium compound imagewise when the slide/print is bleached. As the bleach is rehalogenating, the original image density is gotten back by redevelopment and the chromium compound adds additional density to it. Thus there is increase in density and it is imagewise - denser regions in the slide/print acquire more density than lighter regions. For rehalogenation to go to completion, there should be sufficient amount of Cl- ions available in the bleach. If the goal is to have control over the degree of intensification, then it is best to partially bleach the slide/print i.e. pick up the slide/print before it is fully bleached, clear, wash and redevelop. In this case, chromium compound will be added only to the extent the slide/print was bleached and the original image density is gotten back.
    Last edited by Raghu Kuvempunagar; 19-Jan-2021 at 02:18. Reason: clarity

  7. #17

    Re: Trying out Chromium intensifier

    verry good advice

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