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  1. #141

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    Quote Originally Posted by R Paul View Post
    to R Shaffer
    Yes I liked gp-2 myself. Ascobate developers worked but the images faded out after 2-4 months. Also found that two isopropyl alcohol baths one at 70% and one at 90+% for two minutes each after developing really helped bring out the image.
    The recipe I use came from Darran Green, who is really great about helping curious but clueless people like myself get a handle on this. I can PM it to you if you like.
    There are modern papers written on Lippman photography, naturally I can't recall any now except the SPIE (society of photonics ,imaging and light) had a few. I would have to go and dig them up to see what I have

    rob
    Interesting on the alcohol baths, I'll need to give that a try next go around. I already have Darran Greens instructions for making the emulsion, kudos to you for pulling it off. It looked to complex for me to handle. I got a lot of help from Darran, Hans Bjelkhagen and others here on the list to get as far as I did. I definitely qualify as a 'curious but clueless' in oh so many ways.

  2. #142

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    Quote Originally Posted by Hologram View Post
    Here's Jeff' Blyth's explanation (http://holoforum.org/forum/viewtopic...t=67&start=0):

    However in the case of hologram treated with citric acid and then blow dried at room temperature we are left with a swollen gelatin which is different from the case of one swollen with water plus sorbitol or glycerol. In citric acid we have in effect the line of 3 carbons ins glycerol now with their alcohol groups (-OH) replaced by carboxylic acid groups (-COOH) except for the central carbon which has the (-COOH) added in place of H leaving one alcohol OH still there (mor on this later). These -COOH groups introduce a different effect to cause the swelling of the gelatin. This time the citric acid (-COOH) groups can partially displace the original internal (-COOH) groups from their attraction to the amino groups. Thse displaced (-COOH) groups are still firmly attached to the gelatin biopolymer of course and are not free to wander off in solution so the rest of the citric acid molecules is forced to be accomodated into the gelatin structureas most of the surrounding water is now evaporated off thus leaving the gelatin in a swollen state when it is left to equilibrate with ambient humidity.-- Fortunately it is a chemically weak arrangement easily completely reversed by plenty of fresh water so that it becomes energetically more favourable for all the ions involved to go back to surrounding themselves with water-molecule clouds again. The upshot of this is that if you are not satisified with the color of your treated hologram you can go back to square one without any difficulty.

    One might add that the citric/succinic acid treatment is muss less aggressive to the emulsion than chemicals like urea for example.

    This makes me smile. I can get as far as the 1st sentence.... and then woooosh

    it goes right over my head. I really should have tried harder in college chemistry. Having said that, I can follow directions, so here is another thing to try out.

  3. #143

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    Quote Originally Posted by Photo Engineer View Post
    The action of Urea is reversible, but it depends on hardness, hardening (type of hardener) and a number of other conditions.

    Now, type of hardener is important as chrome and alum type hardeners can be undone but aldehyde hardeners generally cannot be undone. So, you see my point I hope. (it depends)

    Sorry I cannot be more specific.

    PE
    What I was worrying about was that ,if you oversoak a lippmann plate in glycerin solution, it ruins the color effect, but a soak in water will reverse that and bring you back to where you started from. I want to keep that ability. Also wouldn't want to change the chrome alum. too little and the emulsion dissolves off the plate,too much and I figure you wouldn't get any Lippmann effect at all.

    In fact, once I shot a plate backwards in the camera (by accident),
    I soaked it in 10% formalin for 40sec and developed it. Turned out to be a beautiful image like an ambrotype; a negative on transmission ,but a positive on reflection

    rob

  4. #144
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    Wow, looks like a can of worms has been opened.

    Great stuff.. it goes to figure that swelling would be as important for Lippmann's as it is for holography. To what degree of perfection can you dial in a color with swelling of holograms?

    Could the hardening step be incorporated in a fixer? I know that the common wisdom is to not fix Lippmanns, but isn't there a danger of the image fading over time? This seems like a stumbling block.

    I forget if I mentioned it, but supposedly Yves Gentet is working on a Lippmann plate with an integral reflector, a la the original mercurcy, but of course easier and safer. I heard this straigth for the horses mouth, Yves himself. I really hope he succeeds; we could be on the verge of a Lippmann revolution.

  5. #145

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    I think citric and succinic acids were used with dichromated gelatin holograms, not silver halide. The one time I tried citric acid with DCG it melted the coating right off the plate, so I never tried it again..
    As for fixing lippmanns, I never did ,except for the backwards one I mentioned earlier . Just gp-2 , two alcohol baths and done. I haven't noticed any darkening in the older ones (2006).
    I hope he can make those plates . It would remove a big bunch of variables from the equation. Wonder what material he is using for a reflector and how much they will cost?
    rob

  6. #146
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    Since hardened gelatin hardens at the amino groups in all types of processes using aldehydes and tanning, I cannot see how citric acid is able to soften gelatin or swell it, once hardened properly by these methods. Hardening by Alum and Chromium are different and reversible by acid / base treatment. So, a strong acid can possibly displace the metal ion.

    In any event, citrates are not known as softening/swelling agents. The only one I can think of OTOMH is Urea, as I mentioned before. I might also add that there are reported cases of amino acids causing swelling or softening of gelatin.

    I have no direct knowledge but suggest that you try before you decide and leap!

    PE

  7. #147

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    Quote Originally Posted by R Paul View Post
    I think citric and succinic acids were used with dichromated gelatin holograms, not silver halide.
    Actually, the whole thing did start with AgX materials. One issue was shifting 532nm exposures to a "redder" wavelength by post-swelling the emulsion.
    And of course there's the background of the SMART HOLOGRAMS, which exploit differences of the swelling behavior of certain recording media in order to make many kinds of holographic sensors (from devices to measure the amount of water in kerosene to medical applications). They used to be based on AgX technology most of the time.
    DCG only came later. But in that area it would be a significant achievement to finally resolve a problem (shifting the reconstruction wavelength towards a longer wavelength) that has been intriguing people involved with DCG for such a long time.


    Quote Originally Posted by R Paul View Post
    The one time I tried citric acid with DCG it melted the coating right off the plate, so I never tried it again..
    As for fixing lippmanns, I never did ,except for the backwards one I mentioned earlier . Just gp-2 , two alcohol baths and done. I haven't noticed any darkening in the older ones (2006).
    Yes, that's what I did too, both for the homegrown "Lippmanns" and Russian holographic AgX emulsions.
    I always assumed the silver solvent (thiocyanates mainly) in the colloidal developer did remove all the unexposed AgX grains (if present in the right amount) to have them reduced on the exposed grains. So it involves kind of a fixing action.

  8. #148

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    Quote Originally Posted by Photo Engineer View Post
    In any event, citrates are not known as softening/swelling agents. The only one I can think of OTOMH is Urea, as I mentioned before. I might also add that there are reported cases of amino acids causing swelling or softening of gelatin.

    Now they should become known. Citric acid nicely post-swells an AgX emulsion (hardened with a compatible hardener).
    I guess it really is a novelty. I can't seem to find a parallel in photography - putting Lippmann photography aside - where such subtle emulsion swelling would play a role.

  9. #149
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    I'm sure that Citric Acid acts as you say. I'm just saying that I am unaware of any use of it as a swelling agent. I guess it was due to the fact that we tried to reduce swell. We also had some excellent swelling agents in hand such as urea and pH itself.

    BTW, the old color paper stabilizer bath was a pH 3.5 citric acid bath later changed to pH 4.5. In this, we never observed excessive swell. So there must be something going on here more than meets the eye or more than can be logically figured out.

    PE

  10. #150

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    Quote Originally Posted by Photo Engineer View Post
    I'm sure that Citric Acid acts as you say. I'm just saying that I am unaware of any use of it as a swelling agent.
    I think that's no surprise. The swelling effect of say citric acid is pretty small in "photographic terms". Bathing the hologram in a 5 - 10% citric acid solution may shift the reconstruction wavelength from 530 to maybe 580nm. This would make a moderate 10% increase in layer thickness.



 

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