Something for Friday - Panchromatic Dichromated Gelatin

Discussion in 'Alternative Processes' started by holmburgers, Oct 21, 2011.

  1. holmburgers

    holmburgers Member

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    http://sutlib2.sut.ac.th/sut_contents/H95009/DATA/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. Hologram

    Hologram Member

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    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. R Paul

    R Paul Member

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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. Hexavalent

    Hexavalent Subscriber

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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. :sad:
    That's where the experiment ended. That was a long time ago. I've learned a little more chemistry since :wink:
     
    Last edited by a moderator: Oct 22, 2011
  5. Hologram

    Hologram Member

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    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.


    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...



    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. R Paul

    R Paul Member

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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. Hologram

    Hologram Member

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    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?
     
  8. R Paul

    R Paul Member

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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. holmburgers

    holmburgers Member

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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?
     
  10. Hologram

    Hologram Member

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    You'd have to fine tune - as you'd have with AgX emulsions - by adjusting the dye concentrations.

    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/net54holoarchive/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.
     
  11. holmburgers

    holmburgers Member

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    Wouldn't those researchers have tuned the emulsion for even exposure, or is that of little concern with holography? I guess it doesn't matter and so maybe they just didn't take the extra effort to do so?

    That AgX/DCG discussion was very interesting. It makes sense to me on a very superficial level (thinking carbro reaction), but that's about it. It was mentioned briefly, but does this result in better spectral sensitization or speed?

    I'm going to look at this Kodak patent...
     
  12. Hologram

    Hologram Member

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    It certainly is a concern but keep in mind we're making holograms with extremely narrow bandwidth light. So even when doing "full color" holography everything is focused just on a few laser lines (say, 633nm, 532nm, 457nm). Hence, having a spectral sensitivity from 400 - 700nm my be a bit of overkill in most cases.


    I don't know for sure. With all due caution - if it was true - what the Bulgarian research group (Mazakova) was claiming, it would suggest maybe twice the speed of the TMG system.
     
  13. holmburgers

    holmburgers Member

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    Stepping back a bit... how can we compare the speeds of these sensitized DCG schemes versus plain old carbon-printers DCG?

    Or it might be easier to compare a simple unsenstized DCG hologram exposure with one that's been sensitized.

    If there was a relatively easy method to make a faster dichromated-gelatin, it could certainly appeal to carbon printers. I'm not expecting to find some holy grail or anything, but it's certainly possible that carbon printers could benefit in some way from the researches of the holography community.

    It at least makes for a fun discussion!

    How about diazo/azido hardeners? Do holographers use these?
     
  14. Hologram

    Hologram Member

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    From my correspondence with deceased "gummist" Katherine Thayer I had learned that there was one big difference between carbon printing and DCG: carbon printing essentially relies on a photoresist (a surface relief) material. After the photographic exposure the material is processed to remove the non-exposed areas from the layer. For a couple of special holographic applications that kind of processing can be done as well (even with dichromated gelatin) but it's usually reserved for special applications only - the most important one being the making of master holograms for embossing.
    Most holographic recording processes are based on volume recordings, that's to say, the information is recorded throughout the depth of the recording medium.

    Surface relief processes seem to require substantially higher exposure levels than volume recordings. On the other hand, very powerful metal halide lamps are available. So to expose these materials in the visible range may not be that interesting, I don't know.
    On the other hand, I always wondered about the use of lasers for photographic applications - particularly now, where certain lasers (Bluray lasers at 405nm, the 445nm laser diodes from the Casio beamer or 532nm DPSS) have become rather cheap lately.


    ...and vice versa, hopefully. There may still exist some half forgotten photographic techniques that might see a revival in holography someday.



    To the best of my knowledge there has been little use of diazo materials in holography - one big exception though are the Shipley's photoresist materials, currently used by embossing companies.

    From what I gathered one issue involving diazos may be their relatively low speed. I seem to remember Kosar that they are most sensitive below 350nm - though some diazo compounds may also be spectrally sensitized. Over all, Id epxect radically polymerized photopolymer systems to provide better speed.
     
  15. holmburgers

    holmburgers Member

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    A laser-based enlarger that could project b&w negatives onto some kind of sensitized DCG-carbon tissue would be, well.... awesome.

    Holography is so fascinating... thanks for sharing your expertise as you are often wont to do.
     
  16. holmburgers

    holmburgers Member

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  17. Hexavalent

    Hexavalent Subscriber

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    I add glyercine to my carbon-transfer "glop" as a humecant - can't say I've seen noticable increase in speed :sad:
    There is some alum in the formula listed on that web page, so perhaps that's part of the equation.
     
  18. holmburgers

    holmburgers Member

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  19. Curt

    Curt Subscriber

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    Methylene blue was used in Lymphangiograms. The blue stains anything and everything it comes into contact with.
     
  20. Hologram

    Hologram Member

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    This is a volume recording medium (involving refractive index changes throughout the recording layer) - whereas in the case of carbon-transfer you're creating a surface relief structure by washing away the non-light struck areas.

    In the "G307" method the alum only serves to increase the overall gelatin hardening. It's use is not mandatory.
    The role of the glycerol is to enhance the gelatin crosslinking in the "light fringes" during the heat treatment subsequent to the holographic exposure (heat + glycerol slightly reduce Cr5 to Cr3. It's believed that the holographic exposure does convert Cr6 to Cr5 in the "light fringes"). Moreover, adding glycerol to the gelatin may actually allow for larger amounts of dichromate without the risk of crystallization. That might be important given the low absorption of 532nm radiation...
     
  21. holmburgers

    holmburgers Member

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    That's right.. we can't forget that the holoraphic use of DCG is different from carbon and unfortunately I still dont' understand that difference well enough.

    Crystallization though... that's very interesting.