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Thread: Obsidian Aqua, catechol staining developer

  1. #11

    Join Date
    Sep 2003
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    New Berlin, Wi
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    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by Jay DeFehr View Post
    John,

    Yes, the stain is proportional, and the same brown-ish color as other catechol staining developers.

    Evan,

    In my tests, OA produces a speed increase of about 1/3-1/2 stop over box speed with Low Frequency Agitation, and rotary processing costs up to a full stop, or about 1/2-2/3 stop under box speed. Except for the speed loss, OA is excellent for rotary processing, producing no fog or general stain, and very even development with no streaking or mottling, but it really shines with Low Frequency Agitation, where it produces maximum acutance and compensating effects. But, if you can live with the speed loss, I think you'll be very happy with your results from rotary processing, too.
    I'll try to post an example of OA with rotary processing.

    Thanks, I rate 400 TMY at 320 when metering and Pyrocat MC is one of my developer choices, I always make at least two duplicate sheets. I'll make this tomorrow and compare this weekend..Thanks, Evan
    Last edited by evan clarke; 16-Feb-2012 at 12:38. Reason: Operator error

  2. #12

    Join Date
    Apr 2009
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    334

    Re: Obsidian Aqua, catechol staining developer

    Anyone knows where you get catechol in Canada?

    /gth

  3. #13

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    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by evan clarke View Post
    Thanks, I rate 400 TMY at 320 when metering and Pyrocat MC is one of my developer choices, I always make at least two duplicate sheets. I'll make this tomorrow and compare this weekend..Thanks, Evan
    Great! I look forward to your impressions.

  4. #14

    Join Date
    Jan 2007
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    Humboldt County, CA
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    5,093

    Re: Obsidian Aqua, catechol staining developer

    Dang, Jay...you are about to drag me back to pyro...

  5. #15

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    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by Vaughn View Post
    Dang, Jay...you are about to drag me back to pyro...
    Vaughn, I think it's an ideal developer for your work, and your development method (trays, right?).

  6. #16

    Join Date
    Apr 2009
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    334

    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by gth View Post
    Anyone knows where you get catechol in Canada?

    /gth
    Trying again!

  7. #17

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    Sep 2003
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    Re: Obsidian Aqua, catechol staining developer


  8. #18

    Re: Obsidian Aqua, catechol staining developer

    Jay, a little mistake.
    "Dilute 1:500 with 6.66% carbonate solution (sodium or potassium, depending on which metabisulfite is used in the OA stock solution). 1 liter of Obsidian Aqua makes 500 liters of working solution. " You need a carbonate dilution with 6,66g in each liter (1000 ml), and this means 0,666% not 6,66%. This solution have a pH of 11,14.
    I suppose when you mix with the catechol and metabisulfite of part A, the pH lower to around 11.
    Claudio Szarfsztejn

  9. #19

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    Re: Obsidian Aqua, catechol staining developer

    Quote Originally Posted by ClaudioSz View Post
    Jay, a little mistake.
    "Dilute 1:500 with 6.66% carbonate solution (sodium or potassium, depending on which metabisulfite is used in the OA stock solution). 1 liter of Obsidian Aqua makes 500 liters of working solution. " You need a carbonate dilution with 6,66g in each liter (1000 ml), and this means 0,666% not 6,66%. This solution have a pH of 11,14.
    I suppose when you mix with the catechol and metabisulfite of part A, the pH lower to around 11.
    Claudio Szarfsztejn
    Thanks for the correction, Claudio. Your pH calculation looks about right, too.

  10. #20
    funkadelic
    Join Date
    Sep 2008
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    Nashville, TN
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    1,250

    Re: Obsidian Aqua, catechol staining developer

    Jay,
    Your mention of "produces no fog or general stain" drives me to ask... would this developer be a better choice than others when using older films from the freezer that may have a growing density of base + fog as they age (i.e. Super-XX)?

    Chris

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