Dichromate method & density

Discussion in 'Alternative Processes' started by Shinnya, Mar 16, 2006.

  1. Shinnya

    Shinnya Advertiser Advertiser

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    Hi,

    I am in the middle of printing Pt/Pd, and I am a little confused about the dichromate method and the change of the density.

    It seems that as I change to a higher contrast developer, the density goes lower. So, I need to change the time every time I change the contrast. I was under an impression that I adjust the highlight by time and shadow is go deeper as I change the contrast. Was I totally mistaken to think this way?

    How do people usually figure out the time and contrast with this method? Any good idea for the work flow?

    Thanks.

    Warmly,

    p.s. by the way, I am using potassium dichromate like Sandy suggested...
    Tsuyoshi
     
  2. Shinnya

    Shinnya Advertiser Advertiser

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    Hi,

    I should do a little search before I post a question. I did find something about bleaching if higher contrast developer like #4 is used with Pd prints. I am mixing 1:9 (pt/pd). It certainly does look lighter in shadow. Is this because of bleaching?

    Also, about the amount of dichromate, I am getting different information. Some say 1 drop per 200ml and others say 1ml per 200ml. My understanding is that 1 drop is 0.05ml. It does not sounds like they are talking about the same amount...

    Thanks again.

    Warmly,
    Tsuyoshi
     
  3. sanking

    sanking Member

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    With the dichroamte control method you basically match the amount of dichromate you add to the developer to the density range of your negative. For that reason you need to have a separate solution that covers the varying DR of your negatives. I develop my in-camera negatives to a DR of about 1.8, and try to get the same contrast with digital negatives. This limits the number of separate solutions I need to have on hand to two or three.

    Although your experience may be slightly different from mine due to paper choice and chemistry here is the method of control I keep for printing with pure palladium.

    1. Negative DR --1.80 1ml of a 5% potassium dichromate solution per liter of developer.

    2. Negative DR -- 1.60 2ml of the 5% PD solution per liter.

    3. Negative DR -- 1.40 4 ml of the 5% PD solution.

    4. Negative DR -- 1.20 8 ml of the 5% PD solution.

    I don't recommend using more dichromate than this because of the increased grainy look that results.

    Drops vary also, but generally 1ml equals about 20 drops.

    Sandy




     
  4. Shinnya

    Shinnya Advertiser Advertiser

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    Sandy,

    Thanks for clarification about the amount of Dichromate. The amount you mentioned is the exact mix that I am using.

    One question. When you change a developer to a developer with higher concentration of dichromate, does it affect highlight or shadow? That is also what I would like to confirm.

    Thank you again.

    Warmly,
    Tsuyoshi

    p.s.: DR is a little bit beyond my capacity since I cannot measure my negatives yet... Is that something I can measure with step tablet?
     
  5. sanking

    sanking Member

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    A developer with a higher concentration of dichromate affects all densities to some extent, but primarily highlight densities first, then mid-tone densities, and finally shadow densities. Normally in adjusting the contrast of a negative with the dichromate control method there is no need to change exposure. However, if you need to add dichromte beyond about 8ml of a 5% solution per liter of developer you might have to add some exposure time to compensate for density loss.

    Sandy

     
  6. donbga

    donbga Member

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    Tsuyoshi,

    My experience with dichromate in the developer is that it does affect the highlights first. You might want to print a step tablet with each of the different dichromate concentrations to get a feel for how the print contrast changes and the effect on the speed of the sensitiser. So yes it is something you can measure with a step tablet.

    Don
     
  7. Allen Friday

    Allen Friday Member

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    I use the dichromate method for contrast control in my pl/pt prints. I think the main problem you are having is that you are deciding on the proper exposure based on the highlights. This method works for silver paper, but not for pt. Set the exposure based on the shadows. Once you have good shadows, then adjust the highlights by changing the amount of dichromate in the developer. Once the shadows are set, the highlights will fall into place pretty quickly with minimal change to the exposure time.

    This is the opposite of the way most people print with silver paper. This is because the dichromate acts as a restrainer on the highlights. As you add more dichromate, the highlights get help back in their development. Dick Arentz discusses this is his book on pt printing and recommends setting the shadows first. Sorry, I don't have a copy of the book here, so I can't give you a reference to the page.

    Allen