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  1. #1
    holmburgers's Avatar
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    Something for Friday - Panchromatic Dichromated Gelatin

    http://sutlib2.sut.ac.th/sut_content...TA/5636_40.PDF

    Here is a paper about making a panchromatic dichromated gelatin plate for use in holography. But, anyone who does carbon printing will probably have their curiousity piqued by this statement!

    The preparation is surprisingly simple (just by looking at it at least), and the sensitizing dyes are Methylene Blue and Rhodamine 6G; easily available on eBay at low prices. Potassium chromate is used, as is TMG. pH is adjusted to 9.18 with TMG or Acetic Acid.

    THAT'S IT!

    The holography community speaks of things in a slightly different manner, but the basic mechanisms going on here are the same.

    Also interesting are pages 7 & 8 which mention two methods to protect a sensitzied-DCG plate from degradation from atmospheric effects. Physical and chemical sealing. Not sure if these would work with carbon per se, but again, intriguing...

    Lastly, there's a substantial increase in speed. How much?.. I can't say. Pehaps someone versed in milli-joules per centimeter squared can translate this statement,

    "From Fig. 2, we can find that high diffraction efficiencies can be achieved for all the four used laser lines, and the exposure required to obtain a diffraction efficiency of 80% is about 35 mJ/cm2 for 633nm He-Ne laser, 25 mJ/cm2 for 488nm Ar-ion laser, 25 mJ/cm2 for 442nm He-Cd laser, and 15 mJ/cm2 for 514nm Ar-ion laser, respectively. Such a photosensitivity is significantly higher than other red-sensitive dichromated gelatin or blue-green-sensitive dichromated gelatin."

  2. #2

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    Quote Originally Posted by holmburgers View Post
    http://sutlib2.sut.ac.th/sut_content...TA/5636_40.PDF

    Here is a paper about making a panchromatic dichromated gelatin plate for use in holography. But, anyone who does carbon printing will probably have their curiousity piqued by this statement!

    The preparation is surprisingly simple (just by looking at it at least), and the sensitizing dyes are Methylene Blue and Rhodamine 6G; easily available on eBay at low prices. Potassium chromate is used, as is TMG. pH is adjusted to 9.18 with TMG or Acetic Acid.

    THAT'S IT!

    The holography community speaks of things in a slightly different manner, but the basic mechanisms going on here are the same.

    Also interesting are pages 7 & 8 which mention two methods to protect a sensitzied-DCG plate from degradation from atmospheric effects. Physical and chemical sealing. Not sure if these would work with carbon per se, but again, intriguing...

    Lastly, there's a substantial increase in speed. How much?.. I can't say. Pehaps someone versed in milli-joules per centimeter squared can translate this statement,

    "From Fig. 2, we can find that high diffraction efficiencies can be achieved for all the four used laser lines, and the exposure required to obtain a diffraction efficiency of 80% is about 35 mJ/cm2 for 633nm He-Ne laser, 25 mJ/cm2 for 488nm Ar-ion laser, 25 mJ/cm2 for 442nm He-Cd laser, and 15 mJ/cm2 for 514nm Ar-ion laser, respectively. Such a photosensitivity is significantly higher than other red-sensitive dichromated gelatin or blue-green-sensitive dichromated gelatin."
    For quite a while I've been wondering about applying panchromatic DCG to photography as well. By the way, this paper by the Chinese group is actually based on an invention of Jeff Blyth - see GB 2232263, where he suggested slightly different dyes for panchromatic DCG (methylene blue, thionine, riboflavine, phenosafranine).
    I've very limited knowledge about carbon processes. How would it be possible to incorporate a RGB scheme into one gelatin layer? Where I see high potential for panchromatic DCG though is Lippmann photography...

    As for the exposure levels from blue to red, they're certainly well above those of the 350 - 410nm range (probably by a factor of more than 10).

  3. #3

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    Hi
    How would you use this sort of plate for Lippmann photography.
    Expose the plate in a camera, and then process like a hologram?
    I wonder what the exposure time would be? My silver halide plates ran about 3-4 minutes.
    It does sound interesting--DCG holograms are very,very bright when everything works--- It might be worth a go,just to see what happens

  4. #4
    Hexavalent's Avatar
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    I tried methylene blue in a carbon-transfer 'glop' thinking that I'd end up with wonderful, fast, red-sensitive material. What I ended up with is a bright blue glop that stained everything.
    That's where the experiment ended. That was a long time ago. I've learned a little more chemistry since
    Last edited by Hexavalent; 10-22-2011 at 06:57 PM. Click to view previous post history.
    - Ian

  5. #5

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    Quote Originally Posted by R Paul View Post
    Hi
    How would you use this sort of plate for Lippmann photography.
    Expose the plate in a camera, and then process like a hologram?
    Exactly. I'm not entirely sure what processing Gabriel Lippmann had access to when he used dichromated materials (albumin mostly). He reported to have been able to replay these photographs only by wetting (breathing on) them or, by forming AgI finally within the layer in order to swell it.

    Undoubtedly DCG processing will provide very high index modulation. I'm not sure but color fidelity may not be quite as accurate as with AgX. However, due to the increased bandwidth (based on the experience of a single line holographic exposure), color rendition will become much more vivid.


    Quote Originally Posted by R Paul View Post
    I wonder what the exposure time would be? My silver halide plates ran about 3-4 minutes.
    If you're working with home made AgX plates without extra hypersensitization, my guess would be you may have to deal with speed levels of 2-5mJ/cm2. So exposure times around 15 minutes might be a good start...


    Quote Originally Posted by R Paul View Post
    It does sound interesting--DCG holograms are very,very bright when everything works--- It might be worth a go,just to see what happens

    Absolutely. For initial testing, using one dye only may simplify things a lot (Safranine O, which is compatible with Jeff Blyth's TMG system, might be a good choice since it has a fairly broad absorption spectrum).

  6. #6

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    right now I have:
    Quinaldine blue
    Quinaldine red
    Methylene blue
    Malachite Green
    Acridine orange
    Eosin Red
    Rhodamine 6G
    The first two are expensive and I can't get them replaced(the hospital lab closed)
    Eosin works well for green, and methylene blue for red, but it seemed to be Ph sensitive
    I sensitized my plates with an 0.7% ascorbic acid dip and shoot the next day
    and you can adjust the final swelling with a dip in a dilute solution of glycerin (1-2%). Nice thing is if it doesn't work ,you can rinse it out with no damage done

    Question is which dye on the list should I use, since I can't remember which are acid dyes and which are basic( I think it matters)

  7. #7

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    Quote Originally Posted by R Paul View Post
    Question is which dye on the list should I use, since I can't remember which are acid dyes and which are basic( I think it matters)
    Methylene blue, acridine orange, eosin and rhodamine 6G are OK with the TMG DCG system, I assume (generally speaking, I believe any xanthene or thiazine dye will work).

    In the context of AgX emulsions I'm familiar with quinaldine blue (pinacyanol).
    By the way, are you saying you managed to get red sensitized AgX emulsions from methylene blue as a spectral sensitizer?

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    No. I've used it with DCG. The first couple worked, and then I never got good results again. I think it was due to pH, but since I don't have a meter, it would only be a guess.

    rob

  9. #9
    holmburgers's Avatar
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    Hi guys, thanks for the interesting discussion.

    So it sounds like this isn't a balanced RGB exposure? That would be a problem for Lippmann stuff... though perhaps a filter could be used? Then we're looking at hugely long exposure times...

    I didn't have anything in mind by posting, other than in the back of my head the idea of having panchromatic DCG that could be used to make carbon imbibition matrices directly from color negatives or transparencies (relief/planographic matrices respectively).

    The other amazing thing would be to have an enlarger speed carbon tissue or camera speed carbon tissue. Ian, did you notice any speed increase, or was it hard to say?

    Also, are AgX sensitizers and DCG sensitizers two completely different things? That is, would these work with silver emulsions?
    If you are the big tree, we are the small axe

  10. #10

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    Quote Originally Posted by holmburgers View Post
    So it sounds like this isn't a balanced RGB exposure?
    You'd have to fine tune - as you'd have with AgX emulsions - by adjusting the dye concentrations.

    Quote Originally Posted by holmburgers View Post
    Also, are AgX sensitizers and DCG sensitizers two completely different things? That is, would these work with silver emulsions?
    Erythrosine, rose bengal, eosin and perhaps rhodamine G6 may work with AgX to some extent - though they are not as efficient as cyanine dyes.
    On the other hand, cyanine dyes are not compatible with the TMG system.

    However, there's been an other method in the past to marry AgX with DCG: a highly diluted, spectrally sensitized AgX emulsion is mixed with DCG - see: http://www.dragonseye.com/holography...1068398017.htm
    The details of that process remain a bit vague. I've come to believe the AgX has to be AgI in order to form a more stable latent image (without really knowing for sure). It looks like there's has been a forerunner in photography, a Kodak patent (US 1984090, Seymour, Photographic material for making colored prints), which in turn may rely on some 19th century photographic wisdom. It explicitly refers to carbon printing.

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