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  1. #11
    holmburgers's Avatar
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    Quote Originally Posted by Hologram View Post
    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...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.
    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...

  2. #12

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    Quote Originally Posted by holmburgers View Post
    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?
    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.


    Quote Originally Posted by holmburgers View Post
    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 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.

  3. #13
    holmburgers's Avatar
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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?

  4. #14

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    Quote Originally Posted by holmburgers View Post
    Stepping back a bit... how can we compare the speeds of these sensitized DCG schemes versus plain old carbon-printers DCG?
    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.


    Quote Originally Posted by holmburgers View Post
    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.
    ...and vice versa, hopefully. There may still exist some half forgotten photographic techniques that might see a revival in holography someday.



    Quote Originally Posted by holmburgers View Post
    How about diazo/azido hardeners? Do holographers use these?
    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.

  5. #15
    holmburgers's Avatar
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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.

  6. #16
    holmburgers's Avatar
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    http://www.holowiki.org/index.php?ti...07_DCG_Formula

    "This is Jeff Blyth’s formula for plates that exhibit an increased sensitivity to the green wavelengths 514 and 532."

    It's interesting that glycerine is claimed as the sensitivity booster in this DCG-hologram recipe.

  7. #17
    Hexavalent's Avatar
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    Quote Originally Posted by holmburgers View Post
    ...

    "This is Jeff Blyth’s formula for plates that exhibit an increased sensitivity to the green wavelengths 514 and 532."

    It's interesting that glycerine is claimed as the sensitivity booster in this DCG-hologram recipe.
    I add glyercine to my carbon-transfer "glop" as a humecant - can't say I've seen noticable increase in speed
    There is some alum in the formula listed on that web page, so perhaps that's part of the equation.
    - Ian

  8. #18
    holmburgers's Avatar
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    Yeah, that's what I wondered about. If you read the Q&A at the bottom it says "It is the dark reaction additive [of glycerin] that gives the G307 its increased sensitivity."

    Here's a video that I found which might very well explain it (though I haven't watched it yet) -> http://river-valley.tv/improving-the...n-laser-light/

  9. #19
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    Methylene blue was used in Lymphangiograms. The blue stains anything and everything it comes into contact with.

  10. #20

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    Quote Originally Posted by Hexavalent View Post
    I add glyercine to my carbon-transfer "glop" as a humecant - can't say I've seen noticable increase in speed
    There is some alum in the formula listed on that web page, so perhaps that's part of the equation.
    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...

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