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  1. #181
    Photo Engineer's Avatar
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    The Lippmanns that I saw had no Mercury as far as I could determine. They did not seem to be heavy at all. But, they were in a frame and I could not even tell for sure if there was a mirror present. I suspect that there may have been a mirror to enable the image to be as bright as it was in each of these. They can be made available for viewing during the October workshop at GEH.

    PE

  2. #182

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    Quote Originally Posted by holmburgers View Post
    Now, the thing that has me wondering is whether or not you can just leave the emulsion on the mirror during processing & for viewing. There seems to be some disagreement, or at least a lack of clear concensus on this.
    You can leave the emulsion on the mirror for processing, Chris - but not for viewing. To what extent this is doable practically is another matter (you've to struggle with two opposing issues: on the one hand the emulsion must remain on the mirror/glass plate during processing and on the other hand, you have to be able to remove the developed layer from the mirror without damaging it subsequently).


    Quote Originally Posted by holmburgers View Post
    J.S. Friedman in the History of Color Photography clearly states that the mirror must be present for viewing, and that this is of course difficult with mercury.
    I've Just had a look into Friedman: "...the illumination of these plates must be in accordance with the taking scheme; that is, with a mirror in contact with the print so that standing waves will be reformed. For this reason, the plates can be viewed only at a certain critical angle."

    Friedman is just plain wrong about this. Obviously, he is confusing the mirror (reflector, mercury layer etc.) used during recording with the glass wedge, which the Lippmann photograph used to be optically contacted to for better viewing. The 10° wedge simply serves to shift the viewing angle away from the specular reflection of the glass surface.

  3. #183
    Struan Gray's Avatar
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    Bear in mind that most metals which are good for making a front surface mirror will be affected by the processing of the emulsion. Platinum or Palladium are (perhaps) exceptions, but not cheap. Aluminium, nickel or other shiny, broadband reflective metals will all be etched and/or interfere with the photographic reactions. Gold is yellow.

    If you have a set of silver fringes suspended in gelatin with the right spacing, they will automatically reflect light back at the right wavelength. The effect will be strengthened by reflection off the back of the emulsion. The refractive index mismatch between gelatin and air will do this on it's own, but silvering the back will make the effect stronger still.

    These days, I suspect the best method would be to vacuum coat the rear of the emulsion with Aluminium after processing.

  4. #184
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    Martin, thanks for the response, that's precisely the line I was referring to.

    I wondered if that could be the case; I know that even the most careful of researchers can be mistaken. Perhaps it is corrected in subsequent editions? My book is from 1946 (IIRC), 1st edition.

    However, Struan's post puts us back in contradiction; saying that the reflector will strengthen the effect.

    Can the reflector remain for viewing or not? that is the question

    It seems that with the reflector present, there would be no way to produce a black.
    If you are the big tree, we are the small axe

  5. #185
    Struan Gray's Avatar
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    I have not made or seen Lippmann emulsions, but I am a physicist. You don't need a metallic mirror to get a strong reflection (jewel beetles and morpho butterflies do very well with lamellae of chitin and air). However, the silver lamellae in a Lippmann emulsion are created with a metallic reflecting surface on the back of the emulsion, and it seems clear that reproducing that metallic coating will maximise the wavelength-specific reflection when viewing. The phase shift when light reflects off the back of the emulsion will be the same with or without a metallic layer, but the strength and wavelength dependence will certainly be different.

    Black you get by destructive interference. The light is either absorbed, or scattered to non-viewing angles.

  6. #186
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    Thanks Struan. Indeed it does seem reasonble that a reflector would help the viewing, but with all the talk against it I'm wondering what the deal is.

    I'm curious to see what Hologram will have to say.

    Back to the aluminum; what problems might this pose for processing?
    If you are the big tree, we are the small axe

  7. #187
    Struan Gray's Avatar
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    An aluminium front surface mirror will be clouded and/or etched by quite weak solutions of either acid or alkali. Most developers and stop baths would do the trick. If the gelatin is porous enough to develop the emulsion fully the Al is likely to be corroded. You might be able to do something with a barrier layer of hardened gelatin.

    Al ion in solution also interfere with the balance of Ag redox reactions. Most darkroom books advise against using Al trays for this reason. I'm not enough of a darkroom chemist to say how bad the effects are, but the warning makes sense to me.

    I'm about to go into radio silence for Midsummer celebrations - please don't interpret any lack of response as indifference.

  8. #188

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    Quote Originally Posted by holmburgers View Post
    However, Struan's post puts us back in contradiction; saying that the reflector will strengthen the effect.
    No, it won't. If it would, wouldn't then all interference filters and reflection holograms have such reflectors?
    A reflector may severely weaken image contrast and add noise (reflections).

    Quote Originally Posted by holmburgers View Post
    Can the reflector remain for viewing or not? that is the question
    It can't. All the Lippmann photos I've seen (made on AgX materials) reveal their color effect but on the emulsion side. That might be different though with high index modulation materials like DCG etc.

  9. #189

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    Quote Originally Posted by Struan Gray View Post
    I have not made or seen Lippmann emulsions, but I am a physicist. You don't need a metallic mirror to get a strong reflection (jewel beetles and morpho butterflies do very well with lamellae of chitin and air). However, the silver lamellae in a Lippmann emulsion are created with a metallic reflecting surface on the back of the emulsion, and it seems clear that reproducing that metallic coating will maximise the wavelength-specific reflection when viewing. The phase shift when light reflects off the back of the emulsion will be the same with or without a metallic layer, but the strength and wavelength dependence will certainly be different.
    I guess there's a difference between the Lippmann lamellae and say those of a Morpho butterfly wing. In the Lippmann case you're dealing with a volume recording medium. From what I read about the Morpho butterfly structures, I got the impression they mainly involved surface relief effects (perhaps akin to a "blazed hologram").

    Quote Originally Posted by Struan Gray View Post
    An aluminium front surface mirror will be clouded and/or etched by quite weak solutions of either acid or alkali.(...)

    Al ion in solution also interfere with the balance of Ag redox reactions. Most darkroom books advise against using Al trays for this reason. I'm not enough of a darkroom chemist to say how bad the effects are, but the warning makes sense to me.
    I don't know either. But regarding front surface mirrors I'm sure most of them have a very thin protective(MgO, SiO2 etc.) coating on the aluminium layer.

    Quote Originally Posted by Struan Gray View Post
    However, the silver lamellae in a Lippmann emulsion are created with a metallic reflecting surface on the back of the emulsion (...).
    ... a "bunch" of silver nanoparticles, Ag or AgCl/HgCl2, maybe even HgAgCl2 (after a mercuric chloride bleach) within a gelatin matrix. In any case this is not plain silver.

  10. #190
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    Ok, the fact that you view the color from the emulsion side is probably the most important fact here. Indeed, Friedman is completely wrong in this case.

    I'm very interested in what you physicists and "hologramistes" can do for a modern day reflector. Martin, you mentioned aluminized PET and methods to destroy the reflector, and then Yve's Gentet is supposedly working on such a means as well.

    Here's a theoretical proposition... is there another liquid that would be easier to work with than mercury and more reflective than no mirror whatsoever? For instance, would there be an advantage in using water as opposed to no reflector at all. In the reflector-less, Bjelkhagen method (we'll call it), the reflection comes from the emulsion-air interface, correct?

    I'm just wondering if there's another option that hasn't been tried yet, but I admit to asking this in total ignorance of the necessary conditions.

    Struan, as for Midsummer... har de bra!
    If you are the big tree, we are the small axe



 

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