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  1. #11

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    When I started printing with pl/pd I used the commercially available Palladio paper. The dev. was citrate based and you could increase contrast by adding peroxide to the dev. When I started handcoating I used the same method and it worked quite well. In a liter of dev. I would add 10 ml at a time until I achieved the desired contrast. I was using a mixture of about 25% platinum and 75% palladium so I don't know if it would work with straight palladium. In the course of a day of printing I never noticed any loss of contrast by peroxide evaporating but by the next morning you could start over and dev. was back to where you started. I was using sodium citrate developer at the time.

  2. #12

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    A ditto to Michael's post. For convenience, the dichromate method is great. I coat a stack of paper, dry it and rehumidfy it and it sits in a paper safe. Then, I make the contrast changes with the developer. That way, I see a change in contrast immediately while using a different developer rather than having to coat and dry another sheet of paper.

    I'll also mention this method works particlalry well with a Jobo machine (in which I develop all my film and Pt/Pd prints). That way I don't have to pour developer in a tray and then pour it back into a bottle whenI change developers.

    When people hear that I use a Jobo they often ask if I get developer streaks and I never have in years and years of using it. Just think, I can make anything from 8x10 to 20x24 prints in the space of one big tray.

  3. #13
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    Wow, thanks for all the imput everybody!

    Clay,
    I think gum over would be the way to solve the problem with this print. I've made gum prints but the registration issues were a real pain. Maybe it's time to find a real method of registration because I can see where this could easily(in theory) put the kink in the curve. Any suggestions more sophisticated than a hole punch and paper clips but less expensive than a real pin registration system?

  4. #14
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    Quote Originally Posted by Mateo
    Wow, thanks for all the imput everybody!

    Clay,
    I think gum over would be the way to solve the problem with this print. I've made gum prints but the registration issues were a real pain. Maybe it's time to find a real method of registration because I can see where this could easily(in theory) put the kink in the curve. Any suggestions more sophisticated than a hole punch and paper clips but less expensive than a real pin registration system?
    I register everything by eye on a light table. I simply put a sheet of glass over the negative to flatten it out, and then shift it around until the negative is registered. I tape it down with clear, removable scotch tape.

    I think the main issue in registration is paper shrinkage after the first platinum printing step. I have only found two papers that work well without a lot of pre-shrinking prior to printing the platinum base print: Fabriano Extra White and Whatman's watercolor. Extra White will require you to soak it about 5minutes in 1% oxalic acid to get a decent print. The Whatmans is neutral to slightly acidic, and I discovered today that it does fine even without an oxalic acid pre-coat. i had been treating this paper for the last two years, but I didn't have any prepared today, so I though 'what the hell' and tried it anyway. Print looks great.

  5. #15

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    Let me add a note to Clay's information above...

    If you are going to use paper that needs an oxalic acid dip before printing (for gum) then make the water hot enough that it will also preshrink the paper, so the issue of registration is much less of an issue.

    I register that same way as Clay, and most of the time have not had any problems with incorrect printing, as long as I am careful to check all four corners. It's pretty easy to see if they are out of registration.


    ---Michael
    www.mutmansky.com
    B&W photography in Silver, Palladium, and gum bichromate.

  6. #16

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    Another advantage of the dichromate system of contrast control is that it makes clearing much easier. Some of the papers that I have used with straight palladium are very difficult to clear even with the addition of fairly significant amounts of Na2. However, even a very small amount of dichromate results in almost immediate clearing with these same papers.

    BTW, in case any one is interested here is a table that I worked out for contrast control with pure palladium using potassium dichromate. A stock 5% solution of potassium dichromate is first mixed, using distilled water, and this is added to a liter of developer in varying amounts according to the degree of contrast control required. The only disadvantages of this system are, 1) a separate bottle of developer must be kept for whatever number of contrast situations your negatives may demand, and 2) use of large amounts of dichromate, say 16 ml to 32 ml per liter of developer, may cause a grainy look on the print. This varies a lot with papers, however. But here is the chart. Bear in mind that ES means exposure scale, and while it pertains to the paper process it equates to the required DR of the negative. The amount of dichromate added is per liter of developer. Paper was COT320, sensitizer was 1:1 of 15% sodium chloropalladite plus 27% ferric oxalate (with 3g oxalic acid per 100ml). Paper was double coated, first coating diluted one to one with water. Total of 3m of SC and 3ml of FO per 8X10 sheet.

    Dichromate (5%) ES

    1ml 1.80
    2ml 1.65
    4ml 1.50
    8ml 1.36
    16ml 1.26
    32 ml 1.10

    The tests show quite linear results, with each doubling (with one exception) of the amount of dichromate per liter of solution resulting in a contrast increase of about log 0.15. Also, there is very little speed loss with increasing amounts of dichromate, assuming of course that you base speed on 90% or 95% of maximum density. If you base it on the results of plotting with WinPlotter the results indicate a lot of speed loss, which in my opinion is very misleading.

    Sandy
    Last edited by sanking; 10-26-2004 at 01:05 PM. Click to view previous post history.

  7. #17

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    There are are few caveats regarding the use of dichromate in the developer that must be stated...

    1. Dichromate is bad stuff, so you have to avoid skin contact, inhalation, etc. (everyone uses gloves in the darkroom, right?) I don't use gloves, but I don't ever touch the liquid developer. I use tongs to move the prints around, and wash my hands regularly.

    2. For that matter, Potassium Oxalate is bad stuff, too. In fact, almost every chemical in the darkroom is not terribly good, so just have an intelligent respect for the chemicals and processes.

    3. You will have to keep an eye on the developer to ensure that the contrast does not 'drift'. Actually, all developers will do this as they become contaminated with coating solution as a result of wash-off from the print. Every session, I will pour off a little bit of developer and replace it with fresh developer. This has the effect of helping maintain a constant contrast in the developer.


    ---Michael
    www.mutmansky.com
    B&W photography in Silver, Palladium, and gum bichromate.

  8. #18

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    Yet another bit of information about the dichromate method.

    I have seen it stated in writing that the dichromate method of contrast control should only be used in Pt./Pd. printing with potassium oxalate developer.

    This is not correct. Potassium dichromate is every bit as effective in palladium printing as a control agent with sodium citrate as the developer as with potasium oxalate. In fact, when used in the same amount the results with potassium dichromate and sodium citrate are a virtual mirror image of the results with potassium dichromate in potassium oxalate. Ammonium dichromate also works effectively as a control agent with sodium citrate. I don't know who started the rumor that the dichromate method was only effective with potassium oxalate but I have to assume that it was someone who never actually tried it. There are other permutations I have not tested and can not comment on, i.e. sodium dichromate in sodium and ammonium citrate, ammonium dichromate in ammonium citrate, etc.

    This information might be of interest to some people because the citrate developers, especially ammonium citrate, give much cooler tones with pure palladum (very close to platinum in some cases) than potassium oxalate.

    My advice is to never fully trust the experts. Read what they say and take advantage of their knowledge, but just remember that they, like many of us, sometimes make assumptions without fully testing the premises.

    Sandy
    Last edited by sanking; 10-29-2004 at 08:04 PM. Click to view previous post history.

  9. #19
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    I have a couple of questions about the dichromate method after Sandy's posting to this thread:

    http://www.apug.org/forums/showthrea...1867#post71867

    1. Can I avoid the mixing of potassium dichromate by buying the 2% bottle from Bostick and Sullivan and adding 3 drops of 2% instead of 1 drop of 5%?

    2. How often does the dichromate need to be added to the developer? Is this a one shot thing or over the course of a month will it need to be re-added?

    3. What else should I order from Bostick and Sullivan? I feel odd ordering something which will cost more to ship than the cost of the item ($2.48 for 25mL of 2%). I guess I'll wait until I have some extra cash and order some more palladium and ferric oxalate at the same time.
    Let's see what I've got in the magic trash can for Mateo!

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  10. #20

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    Quote Originally Posted by Jeremy Moore
    I have a couple of questions about the dichromate method after Sandy's posting to this thread:

    http://www.apug.org/forums/showthrea...1867#post71867

    1. Can I avoid the mixing of potassium dichromate by buying the 2% bottle from Bostick and Sullivan and adding 3 drops of 2% instead of 1 drop of 5%?

    2. How often does the dichromate need to be added to the developer? Is this a one shot thing or over the course of a month will it need to be re-added?

    3. What else should I order from Bostick and Sullivan? I feel odd ordering something which will cost more to ship than the cost of the item ($2.48 for 25mL of 2%). I guess I'll wait until I have some extra cash and order some more palladium and ferric oxalate at the same time.
    1.- Yes
    2.- you will have to determine that, I replenish the dichromate in my solutions every 800 sq inches.
    3.- Artcraft is a little bit cheaper.

    I dont know why you dont want to mix it, it is not as bad as it sounds. As I have been trying to say in many posts, mixing of chemicals, if done with care should not be any different than cooking. You keep the kitchen clean, you pick up what you spilled immediately and if you get it on you, you wash right away or change clothes. I ordered 200 gr of potassium dichromate, I still have a hole bunch after 3 years, so far I have not sprouted any extra arms..

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