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  1. #1
    L Gebhardt's Avatar
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    Carbon Printing - Toxicity

    I am thinking of taking up Carbon printing. This is something I have been thinking about for quite a while, but haven't made the push to start primarily because of concerns about the chemicals (Potassium Dichromate).

    I am on a septic system and worried about poisoning myself or the ground water. Can this be done in a safe and environmentally sound manner? What steps and precautions would need to be taken.

    I do have a local hazardous waste collection every couple of months during the warm weather. I don't think it would be feasible to haul all my wash water there however. But I could certainly collect small amounts for processing.

    I also do not have a fume or dust hood, so I am worried about mixing the chemicals because of the dust.

    Are my concerns justified? Any tips on how to do it right?

  2. #2
    Vaughn's Avatar
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    You won't need a fume or dust hood. The dichromate is more of a crystal form rather than a fine powder. Wear a dust mask if you are overly concerned. You make a stock solution, so one is not always using the raw chemical. Also the dichromate does not enter the air via fumes (when, for example,, spirit sensitizing.

    I prefer to spirit sensitize -- using only the amount I need for each tissue (rather than making up baths of dichromate of different strengths that eventually can go bad and one has to deal with solutions of dichromates to get rid of.)

    Not enough in the wash water to even think about -- most will come out in the transfer bath and the development baths.

    There are ways to change the form of the dichromate from the most toxic form to a less toxic form. I am not familiar enough with that to discuss it further. You can set the transfer bath outside and evaporate off the water to reduce volume.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

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    Like Vaughn I spirit sensitize by brushing a mixture of dichromate + acetone on the tissue. Very little is needed, and you are working with very dilute solutions of dichromate, from as low of about 0.5% to a high of about 10%. To sensitize a sheet of tissue 14X20" in size I use only about 20 ml of a 6% solution of dichromate, diluted 1:1 with acetone. If you like it is possible to neutralize the solution but frankly the amount of dichromate used is so small I don't think it is necessary. There is certainly no risk of damage to a septic tank system with the amount of dichromate used in carbon printing as I have been using dichromate in my home for more than two decades.

    Sandy King

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    The best solution, and the one I practice for gum printing, is to capture all dichromated water and bottle it for hauling to a waste site. Same as you should be doing for fixer and the rest of your chems...

    Not familiar enough with carbon process to know about wash water, but with gum I collect the first wash water as well as brush/dish cleaning water.

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    I have for a long time promoted spirit sensitizing because of the very small quantities of dichromate that are used because it makes sense from an environmental point of view. For most of my work it takes about 1.0g of dichromate to sensitize a 14"X20" tissue. If one were to make a hundred carbon prints this size during a year the total amount of dichromate used would be 100 grams, or less than a quarter of a pound.

    On the other hand, some methods of sensitizing use a lot more dichromate because much of it is wasted and goes down the drain. I would encourage anyone who takes up carbon printing to look carefully at the various methods of sensitizing that are proposed by different workers and choose one that is as "green" as possible. In the end all of the methods used to sensitize work well when practiced by a skilled worker so it makes sense IMO to waste as little dichromate as possible.

    BTW, dichromate mixed in distilled water is very stable and can be retained for years and years. I have some solutions on hand that are 5-10 years old and are still as good as when freshly mixed.

    Sandy King

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    smieglitz's Avatar
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    You probably want to check with a chemist on this but adding an alkali (e.g., borax, sodium bicarbonate, sodium sulfite, etc.,) to a used dichromate wash should convert the more toxic hexavalent chromium form to a less toxic trivalent chromium compound. Filter that solution and eventually dispose of any chromate sludge as a toxic solid waste. Then, you could make a trickle tank out of a 5-gallon bucket filled with bentonite cat litter and let the waste solution slowly trickle through that into a drain (or evaporate in the bucket if you don't puncture it and have enough time). The cat litter should chelate (?) any remaining metal from solution if what I've read over the years is sound. You'll end up with a solid waste that needs to be disposed of eventually through a toxic waste disposal service, but I don't think you'd have to worry about the liquid any longer.

    A couple other references:

    http://www.apug.org/forums/forum42/5...sposal-uk.html
    http://www.cartage.org.lb/en/themes/...safedichro.htm

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    L Gebhardt's Avatar
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    Thanks all. Seems like it's possible to do this in an environmentally friendly way without hurting myself. So I'll get some stuff ordered.

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    Quote Originally Posted by L Gebhardt View Post
    Thanks all. Seems like it's possible to do this in an environmentally friendly way without hurting myself. So I'll get some stuff ordered.
    Where do you intend to purchase the Dichromate? Are you going to order Ammonium Dichromate or Potassium Dichromate.

    As to safety, I use the same skills that I learned in Industrial Chemistry in College. Wear gloves and eye protection. I wear glasses and use a small scale to measure the Dichromate by placing the Dichromate on a small piece of paper. I don't come into contact with the Dichromate in this practice as I do it in my darkroom alone with the door closed. No people, distractions and no wind. Since there is so little used there is little washed down the drain at the end of the process.

    As a side note I was talking to my neighbor and trying to explain what a Carbon Transfer print was and he said, "it's like the ball and cap rifle hobby", I said yes, if you make the rifle with hand tools and raw materials first. Hobby, I don't think so.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  10. #10

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    Quote Originally Posted by Curt View Post
    As to safety, I use the same skills that I learned in Industrial Chemistry in College. Wear gloves and eye protection. I wear glasses and use a small scale to measure the Dichromate by placing the Dichromate on a small piece of paper.
    You should also plan to wear protective gloves (latex or nitrile) when immersing your hands in water solutions that contain dichromate, as for example when mating the sensitized and exposed tissue to its final support. The very weak dichromate solutions are not toxic at this point but they can cause severe dermatological problems over time if you work without gloves.

    I would also recommend wearing the gloves when you develop the image in warm water. Repeated dunking of your hands in warm water will wash the protective oils from your hand and may cause cracks in your skin. In the past when I did not use gloves in warm water development I would get painful fissures around my fingernails.

    Sandy King

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