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  1. #11
    sly
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    Some great info here. Thanks!

  2. #12
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    Step wedges are this thing that you get, play with for a little whiles - then forget ...

    (but worth every cent and every second)
    Cleared the bowel problem, working on the consonants...

  3. #13

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    I don't use test strips either, the main variable I find is relative humidity - where I live this can vary from 40% in winter to 75% in summer, and exposure times vary from 6 to 10 minutes.

  4. #14

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    Actually, I think absolute water content of air (and paper) is more important:
    Water content of air at 20C (68F) / 40% RH = ~15g (which is saturation humidity per kg of air at 20C) x 40 / 100 = 6g (per kg of air)
    Water content of air at 30C (86F) / 75% RH = ~28g (same as above, but for 30C) x 75 / 100 = 21g (per kg of air)

    As you can see, the water content of air changed more than 3x while the RH change was less than 2x! (1.875x, to be exact...)

    Another example:
    Water content of air at 20C (68F) / 50% RH = ~15g (which is saturation humidity per kg of air at 20C) x 50 / 100 = 7.5g (per kg of air)
    Water content of air at 25C (77F) / 40% RH = ~24g (same as above, but for 25C) x 40 / 100 = 9.6g (per kg of air)

    Now, things get interesting here; even if 40% RH (at 25C) is numerically smaller than 50% RH (at 20C), the absolute moisture content of air is more in that case, therefore your emulsion will be slightly faster!!! (Even if the RH figure was lower...)

    Moral of the story: Don't be fooled by just taking RH into account; you have to pair that with temperature, in order to be able to make a good educated guess...

    Regards,
    Loris.

  5. #15

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    Interesting analysis, Loris.

    So how many grams of water per square meter does properly humidified paper contain - as an order of magnitude? In other words could this be measured and controlled by weighing a sample of coated paper?

    Ben

  6. #16

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    Ben, I don't know; IIRC, there was such an analysis/test in Mike Ware's Cyanotype book, but I don't have it with me right now...

    I do know that carbon printers analyze the water content of their sensitized and dried carbon tissue by weighting it before and after sensitization; therefore, I assume the method you've described give some useful information indeed...

    Regards,
    Loris.

  7. #17
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    Quote Originally Posted by Paul View Post
    Thanks for the input. I too have been avoiding test strips in favor of starting with an educated guess based on past prints and working from there. I am getting better at it, but have a way to go yet. Glad to have my working methods validated by the experiences of three accomplished printers.
    Test strips can be very effective and save material. Just take care keeping the paper strips at the same humidity level. So yeah I disagree that test strips aren't useful.
    Don Bryant

  8. #18
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    Quote Originally Posted by Ben Altman View Post
    Interesting analysis, Loris.

    So how many grams of water per square meter does properly humidified paper contain - as an order of magnitude? In other words could this be measured and controlled by weighing a sample of coated paper?

    Ben
    The easiest way to control the water content of your paper/coating is to force dry it for a constant time (e.g. with a hairdryer) and then put it in a humidifying tank for a consistent time. The times depend on your paper but are easy to establish by trial.

  9. #19

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    I use a factorial drying time; I time how much a single drop of water (from a plastic pipette, on a piece of glass) takes to dry, and use (say...) 2x of this to dry my paper. 2x is just "a" ratio here, you can freely play with it (1x - 3x - ...), depending on the needs of your current process and the outcome... Works sufficiently fine for me.

    Bone drying then using a humidification chamber definitely works well -> but I don't have space for one myself...

    Regards,
    Loris.

  10. #20
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    I just wanna add a bit of info from my personal experience printing in Pt/Pd.
    I've been making 12x20 pt/pd prints for about 3+yrs now and 7x17 and 8x10s for a few years prior to that.
    And I almost always do test strips. Especially with 12x20. Often I would skip it with 8x10s as the guesstimate method works fine.
    But when it comes to making 12x20 pt/pds and using +/- 1.2 ml of Ferric Ox, +/- 1.2ml of Pd, and a fair amount of drops of Na2 Pt.... the guesstimating method just isn't real practical and feasible.
    I usually have a stack of 4-5 12x20 negs I am printing and will estimate the contrast range Na2 drop count and coat a single sheet of paper with 1.2ml FO, 1.2ml Pd, and an estimated amount of Na2. After that sheet is dried and properly humidified I cut it up and do test strips for all 5 negatives. It's a process that works well with the method of shooting I do.
    Keep in mind that I am NOT working with predictable and measurably precise negatives. I shoot architecture, landscapes, random stuff outside, etc... with Efke PL100 in 12x20 and develop by inspection in PyroHD. So my negs are precisely identical... to say the very least.

    Just and FYI for some variation on working methods.
    Nigel Tufnel: It's like, how much more black could this be? and the answer is none.
    None more black.

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