dichromate in developer

Discussion in 'Alternative Processes' started by Mateo, Oct 24, 2004.

  1. Mateo

    Mateo Subscriber

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    Just curious, what is the advantage of using dichromate in potassium oxalate in addition to Na2 in the coating. The Na2 contrast agent seems to take care of all my negatives so I'm wondering why people also use the dichromate. Anybody?
     
  2. Jorge

    Jorge Inactive

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    I have founnd that I can fine tune the contrast better with the dichromate method. The platinate is such an agressive restrainer that very little goes a long way and sometimes I find it hard to find a small enough dilution to make small changes.
    In my case I only use platinum to preven solarization, so I rarely use platinate as a restrainng agent.
     
  3. Mateo

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    Any idea how little Na2 can be used in the sensitizer? I've been able to get away with 1 drop of 2.5% for an 8x10 without fogging and Kevin Sullivan says that he can do pure palladium prints without contrasting agent. I've been considering the dichromate method but having that many bottles of dev seems to be a pita. Is it worth it?
     
  4. Jorge

    Jorge Inactive

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    I do pure palladium with the dichromate method and it works for me. I guess it is all in how you like to work, it seems to me you are doing fine, why change? If you calibrate everything you will find you only use one or two bottles, and have the rest for emergencies. I typically use my developer #2 and #3. WHich have 2ml dic rhomate/200 ml developer and 3 ml/200 ml. Typically I am working with DRs of 1.4 to 1.6. But I have messed up and done prints with a DR of .6 by using my developer #5 plus 3 drops of chlorate .6%.

    To onaswer your question, to me is worth it, it might not be to you. Your prints are beautiful, if it aint broke, dont fix it.
     
  5. Mateo

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    I guess I'm just looking to do something that ain't possible. I've got a work print with high values and low values right where they belong but I wish the areas at zone VI were closer to zone V. I was hoping that you guys used the dichromate because it effected contrast in a different way than Na2 so that I could put a subtle kink in the printing curve to make the print look like I want it to. The neg is as good as I'm ever going to make one and the zone VI should print where it does I just think it would look better if I could change it. I guess I'll have to dodge/burn or make a mask. Thanks Jorge.
     
  6. clay

    clay Subscriber

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    Mateo:

    i use dichromate in the developer because it will not change the image color of a pure palladium print. I find that on the papers i really like, the Na2 will appreciably cool down the image tone even when used in very small quantities.

    As far as doing what you what with the printing curve, it sounds to me like it may be time for you try gumover platinum. Because the exposure scale of gum is much shorter than palladium, you can do all sorts of tonal curve manipulation by choosing the contrast and exposure of the gum layer. It is a great way to increase the shadow contrast of a print for instance. You just make a platinum prints with weakish low contrast shadow tones, and then put a gum layer on with a short brief exposure. It will pump density in the shadows and leave the highlights alone.
     
  7. Michael Mutmansky

    Michael Mutmansky Member

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    In addition to Clay's response, I feel that the dichromate method is superior to other contrast control methods (including NA2) because it enables a more consistant workflow. I can coat up several sheets of paper, and work with subtle changes in contrast at the developer end, not by recoating more paper.

    I often will try the developer mix on either side of the ideal, simply to ensure that the one I have selected is doing what I want in the image. This is more complicated and time consuming if I have to make coating adjustments to obtain the contrast desired.

    I see NA2 as a last-resort contrast agent, not as the primary method for adjusting contrast. Others have switched to it, but I don't see it working as well in my workflow.

    ---Michael
     
  8. wm blunt

    wm blunt Member

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    I have been using the dichromate in the dev. for most of my printing with using the NA2 very sparingly to just kind of tweak a print once in a while. A mistake I made in the beginning was to mix alit of different cox dev and dichromate combinations and now like Jorge I use mostly #2 and #3 mix. It took me awhile to figure out I could further dilute those bottles like #6 that I didn't use to get a #3 mixture ( I've never been accused of being too bright).
    I like the color of the prints with the dichromate method much better.
     
  9. cjarvis

    cjarvis Member

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    What about peroxide in the sensitizer? I don't know of any way to adjust middle tones without affecting the other ends of the curve, but I'd love for someone to test all the methods and report back. :smile:
     
  10. sanking

    sanking Member

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    A few drops of hydrogen peroxide added to 2ml of sensitizer will get rid of some slight fogging that you may get with pure palladium. The result is similar to what you would get by adding a drop of 2.5% Na2 to the same amount of sensitizer, or adding about 1ml of a 5% potassium dichromate per liter of potassium oxalate developer. However, as far as I know no one has designed a contrast control system based only on hydrogen peroxide.

    On the whole I find both the Na2 method and the dichromate method about equally effective in contrast control. The Na2 method requires fewer solutions and gives good results with low contrast negatives, but gives cooler tones than pure palladium. The dichromate method allows slightly finer contrast adjustments and keeps the warm tones of palladium but gives poor results (grainy prints) with low contrast negatives. Both methods are in my opinion much easier to use than the old A+B method.

    BTW, choice of UV light source may be a way that can be used to change the slope of the curve in the mid tones without changing it in the toe and shoulders. When I compared the curve of a SA light to that of a BL or Nu-Arc metal halide lamp I found that the SA gave a straighter line response with a shorter toe and less shouldering. These results were based on a 1:4 platinum/palladium mix, mixed 1:1 with FO and no further contrast control.

    Sandy
     
  11. wm blunt

    wm blunt Member

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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.
     
  12. wmlaven

    wmlaven Member

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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.
     
  13. Mateo

    Mateo Subscriber

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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?
     
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  15. clay

    clay Subscriber

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    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.
     
  16. Michael Mutmansky

    Michael Mutmansky Member

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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
     
  17. sanking

    sanking Member

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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 a moderator: Oct 26, 2004
  18. Michael Mutmansky

    Michael Mutmansky Member

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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
     
  19. sanking

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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 a moderator: Oct 29, 2004
  20. Jeremy

    Jeremy Member

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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/showthread.php?p=71867#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? :smile: 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.
     
  21. Jorge

    Jorge Inactive

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    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.. :smile:
     
  22. sanking

    sanking Member

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    1. Yes, but the bottle of 2% solution won't go far. Just bite the bullet and buy 100 or 200 grams of potassium dichromate. It will last forever in powder form, or in solution if you mix it with distilled water.

    2. Dichromate does not need to be re-added. All you need to do is top off your developer to replace what is used in processing with fresh developer, adding back dichromate as need.

    3. Palladium printing is very simple. All you need is ferric oxalate powder, potassium oxalate, sodium citrate or ammonium citrate developer, and sodium chloropalladite. You might also want to have on hand a small amount of oxalic acid and/or citric acid depending on which developer you settle on. And either Na2, dichromate or hydrogen peroxide (or other) depending on how you plan to control contrast.

    Sandy
     
    Last edited by a moderator: Nov 1, 2004
  23. Jeremy

    Jeremy Member

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    Jorge, I wanted to buy it pre-mixed because according to Bostick & Sullivan ordering it in powder form necessitates a hazardous chemical charge will probably be about 10x the cost of the actual chemical.
     
  24. Jeremy

    Jeremy Member

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    If I don't need to re-add it, but just mix it in with my developer to top off why would I need so much? I am pretty sure that 100mL (~$3.50) should last me a couple of years if I'm only adding 1-3 drops/liter.
     
  25. Peter Schrager

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    Dichromate

    Jeremy-I'll send you some for free-just PM me your address. Like Jorge said I also bought 5 LBS and it will last forever!
    Regards Peter
     
  26. Jorge

    Jorge Inactive

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    not really, it depends on the amount. I bought it from them and I dont remember being outrageous, or I would not have bought it.

    As to replenishment, I have found that the dichromate does exhaust after repeated uses, even if you are not topping off with PO. I let my bottles go to about 3/4 before I refill with PO, and even before then I see I need to add dichromate after 800 sq inches or my prints starts loosing contrast. This makes sense from the chemistry point of view.

    But heck Peter S is offering to send you some, take him up on it.