Avoiding potassium dichromate in bromoil process

Discussion in 'B&W: Film, Paper, Chemistry' started by kept, Aug 7, 2012.

  1. kept

    kept Member

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    Hello, everyone! I'm new to this forum and new to the bromoil process.
    I wanted to ask are there any possibilities of avoiding potassium dichromate in the bleaching solution preparation? Maybe there are some alternative recipes for this solution? Because it's difficult to obtain it in Lithuania because of its toxicity.

    Cheers!
     
    Last edited by a moderator: Aug 7, 2012
  2. gandolfi

    gandolfi Member

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    not to my knowlegde. The potassiumdichromate acts as a tanning agent. Without, no hardening of the gelatine, and therefore you can't ink it. (it will all be black...)
     
  3. holmburgers

    holmburgers Member

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    Well couldn't you in theory use a tanning developer, a la Kodak's dye-transfer developer? Assuming you've exposed an image onto a "bromide" paper, developing this in a pyro developer with high tanning properties would give you something analogous to a dichromate-bleached print.

    And although this would only work with oil (not bromoil, that is), you could make a diazo sensitized gelatin paper, expose and wash/clear. This would also give you a gelatin image composed of both tanned and untanned gelatin.

    So, there's some food for thought.
     
  4. MDR

    MDR Member

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    Ever since I read about the chiba system I keep thinking that a bleach with Ammonium Ferric citrate and Hydrogene Peroxide should work for Bromoils. But I am not actually sure that it does maybe one our resident chemists can help.

    Dominik
     
  5. artonpaper

    artonpaper Subscriber

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    I can't answer your question, but when it comes to shipping dichromates, here in the US, at least, the powder form requires HAZMAT shipping which is very expensive. I order dichromate from Bostick and Sullivan and I ask them to dilute it to the solution strength I need. For some reason, the dichromate in liquid form doesn't require HAZMAT shipping. Perhaps you can find a supplier who can work with you in that way.
     
  6. Klainmeister

    Klainmeister Member

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  7. holmburgers

    holmburgers Member

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    Wow, that's definitely the best, most concise account of dichromate dangers, history and disposal I've seen all in one place. Thanks for posting.
     
  8. Klainmeister

    Klainmeister Member

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    What's funny about that situation is that we had been working on those oil prints for a while and everytime someone new came by or someone outside heard of the use of dichromate, there was an instant reaction about the dangers involved...yada yada. It seems to never end. Recently playing with a revised formulation of cyanotype we tossed it in a tray of dichromate instead of hydrogen peroxide since none was available. Worked like a charm. Not worried one bit.
     
  9. kept

    kept Member

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    Thank you all very much for the answers!
    It's funny though I've found an old glass vessel almost full of potassium dichromate (according to the formula written on it) in an old photo lab. It's a bit strange it is a white powder not red, as I saw it in Wikipedia. Is it still good to use? Does potassium dichromate have an expiry date?
     
  10. holmburgers

    holmburgers Member

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    Hmmm... I think it's probably not potassium dichraomte then. It's an INTENSE, unmistakable orange, and I don't think it would turn white with time (??)

    And if it is potassium dichromate, I wouldn't want to use it in that state anyways. Always best to avoid messing with "mystery chemicals".
     
  11. Gerald C Koch

    Gerald C Koch Member

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    As a chemist I can't think of any chromium salt that is white. So I would say that it's definitely not potassium dichromate. The element chromium gets its name from the color of its compounds.

    There is an easy test to identify potassium dichromate. Dissolve a small amount in water and a few drops of 3% hydrogen peroxide. A dark blue color is produced which soon fades with the evolution of oxygen bubbles.
     
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  12. oldfaithful58

    oldfaithful58 Member

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    Hi, this is a question for discussion purposes rather than me making a knowledgeable statement:
    If potassium dichromate is used to tan the gelatin, making it hard and stable, would an alternative tanning agent act as a suitable replacement?
    I originally trained as a leather technician, many many years ago, but remember the following: chrome VI salts are most commonly used mineral tannages, with pyrogallol and catechol the main vegetable products. Clearly the potassium dichromate is providing the chrome salt. Pyrogallol complexes have good longer term stability due to buffering however catechols suffer badly from instability in acid environments. There are also other mineral tannages for high stability; aluminium oxide (16 % Al2O3, ca. 50 % basicity).
    Compared to potassium dichromate, this could be considered "nice" - Aluminium oxide was taken off the United States Environmental Protection Agency's chemicals lists in 1988.

    So Gerry or PE, do you think that it may be feasible to replace the tanning action of the potassium dichromate with basified aluminium oxide?
    I haven't done any Bromoil work, but have seriously thought about trying it. This might make the route more available in the near future?

    Dave
     
  13. Wayne

    Wayne Subscriber

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    Good question.
     
  14. Athiril

    Athiril Subscriber

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    That's not potassium dichromate. Likely to be something like sodium carbonate or sodium sulphite.

    Potassium Dichromate has a distinct orange colour, that you can even tell apart from Potassium Ferricyanide's red colour.
     
  15. Wayne

    Wayne Subscriber

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    I'm sure he's thankful for being told that. Again. 4 years later. :tongue:
     
  16. Rudeofus

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    Since this question appears to have been resurrected after four years, allow me to add my two Eurocents: There are two requirements for making a compound work for this process:
    1. The compound has to tan gelatin
    2. It must do this only in the presence of developed silver or developable silver halide, not everywhere
    The second point pretty much puts the "basified Aluminum Oxide" route to rest, since there is no way that the tanning caused by it can be specific to developed silver. Pyrogallol, on the other side, may just work. Note that Pyrogallol is quite poisonous, too, so use it instead of Dichromate only if it's easier to get, and then only with great care.
     
  17. cliveh

    cliveh Subscriber

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    No.
     
  18. Wayne

    Wayne Subscriber

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    Ah, that's no good. I only resurrected it to see if there were less toxic alternatives as I don't trust myself with dichromates and for good reason. Or pyro. I'm too mistake prone.
     
  19. Rudeofus

    Rudeofus Subscriber

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    There were a few threads about staining developers based on Hydroquinone, e.g. this one and this one. Since these developers are much less popular than staining developers based on Pyrogallol or Catechol, there is little to no public data about their suitability for bromoil processing. Given your restrictions it appears to be your only hope at this point, though.
     
  20. Wayne

    Wayne Subscriber

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    Worth a try. I've been experimenting with Q tanning developers anyway.I'm still mulling it over and researching whether I want to give bromoils as try, but if I were to try how and in what quantity would you suggest incorporating Q into the bleach process/recipe?
     
  21. Wayne

    Wayne Subscriber

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  22. NedL

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    Hi Wayne.

    If I get that process "ironed out" and working, I'll write an article about it here.
    It's getting a lot closer, but I have not had complete success yet
     
  23. Rudeofus

    Rudeofus Subscriber

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    Wayne, the Hydroquinone would be part of a specially formulated developer, not part of some bleach. There are two common ways to achieve selective tanning:
    1. Use any developer to develop the image, then use a bleach which tans gelatin wherever metallic silver was bleached. That's the approach chosen by the process using the dichromate bleach.
    2. Use a developer which tans gelatin wherever development takes place. This is what Pyrogallol, Catechol, and apparently also Hydroquinone based developers can do, if they are formulated correctly. No bleach should be necessary here as long as the developer creates sufficient tanning.
    PS: I have never done this process, so I would be the very last one to be asked for sample recipes. Ned's blog appears to be what you should be looking at, and the two links I provided in this thread point towards HQ based tanning developers which have at least been tried.
     
  24. Wayne

    Wayne Subscriber

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    ah thanks. I haven't really studied the oil process in detail only the chemical list so I (obviously)don't have a good grasp of the techniques. I already have a tanning HQ developer so I'll study this all a bit closer.

    I saved your whole blog Ned, in case you want to try to recreate it. I don't see a blog function yet but maybe it could be turned into a thread
     
  25. NedL

    NedL Subscriber

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    Thanks Wayne, I saved it too. Still working on the process!

    Just to be clear, what I'm working on is a ferric oil print. A variation of Rawlins' oil print process. It requires a full sized negative and there is no silver involved.

    A bromoil print is made from photopaper or paper coated with commercial or homemade silver bromide emulsion. It is first printed ( usually with an enlarger, but I suppose a contact print would be fine ), developed, fixed, and then bleached and tanned.

    In the end, both processes end up with a "matrix" of gelatin on paper which has been hardened where light hit the paper, in the shadow/dark areas of the image.

    I'm about 95% sure that the process I'm using wouldn't work on a bleached print to replace bromoil ( I think the ferric would react with the silver ) but maybe someday I will try it just to see if that's right!