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  1. #11

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    Thanks T-Grain,
    This meens that I will put that project way way on the most rear burner. I think that someone will make a gelatin based pan emulsion in the not too distant future. But I do intend to try Jim's idea of adding pigments to a pan emulsion.
    Bill

  2. #12
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    T-Grain;

    The authentic receiving layer in the Dye Transfer process was a Thorium salt in gelatin. The Thorium precipitated the acid dye and therefore created a concentration gradient across the Matrix film into the receiver sheet. This method cannot be used today, but others have found ways to simulate this using Aluminum salts. The ph effect is there, but is a minor actor in the face of a mordant which actually precipitates the dye and totally removes it from action.

    PE

  3. #13

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    Hi Bill - the idea for a carbon tissue utilizing silver halide instead of dichromate UV depends on a hardening action to occur, either when developing in a pyro developer, or using a bleach as in the old Kodak Wash Off Relief process. You would want to verify if either of these two image hardening techniques will work with PVA. The next thing to do is to determine how much pigment you need to get a good DMAX on the print. You would want to make up four types of 'tissue' (I would coat on mylar myself) : Cyan, Magenta, Yellow and Black. The pigments themselves will absorb the exposing light, giving the light penetration limiting effect. Exposure is from the emulsion side, unlike DT. The $10,000 question is: if you put in enough pigment for a good DMAX, can you still expose the emulsion? If speed is too slow, you could always formulate a faster emulsion. I don't think grain will be much of an issue. My guess is that it will work, since the absorbtion of the pigments will be similar to the dyes in Cibachrome, which has a decent DMAX - a slow speed, but usable.

    Regards - Jim

  4. #14

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    Ron and Jim, I thought a Thorium salt was needed just to enhance sharpness not to actually hold the dye in the receiving gelatin?
    Jim, when you say using bleach as in the old wash-off relief process-is this an etch-bleach process?
    thanks

  5. #15
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    T-Grain;

    Thorium is a true mordant in the sense that the Azo-Sulfonate dyes precipitate as a Thorium salt. Today, Guanidinium salts and other positively charged quaternary ammonium salts are used as mordants.

    As I understand it, the Thorium bound so tightly to the dyes that it does enhance sharpness relative to other mordants simply by tying the dye up strongly and quickly, preventing any bleed. Thorium also altered the hue of the cyan dye a tad. Jim probably has more on that.

    PE

  6. #16

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    Ron, have you used any guanidinum salts as mordants in your dye-destruction experiments? BTW, how is going?

  7. #17
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    I had intended to have some new ones done this week, but the workshop occupied too much of my time. Preparation and etc....

    I have no mordant but have used it in experiments at EK. The dyes I have used, can be "self mordanted" due to their high molecular weight. At the present time, I am just imbibing them into the coatings. It works as a quick test.

    I lack a cyan dye though. None of the ones I can get are azo dyes. They are anthroquinones which are not suitable. I prefer using a metal mordant such as Aluminum or the like.

    PE

  8. #18

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    Thank you Jim,
    As of now, I have done exactly nothing to determine whether or not this PVA based panchro emulsion can be used as vehicle for printing pigments. But I have made 2 observations which may be relevent to the question of whether or not the base polymer will harden in pyro developer or a bleach out process. First, in trying to find an alternative to alcohol precipitation, I have found that a 7% of the the silane modified PVA in water will fall out of solution upon raising the pH with 1% KOH. After wahing the precipitate, lowering the Ph with sulfuric acid will not redesolve the polymer, no mater how long or how high the temperature. I conclude that a rise in pH has crosslinked the polymer. I am stil stuck with alcohol precipitation for the purpose of wahing the emulsion.
    Secondly, I have found that pyro developer yields a rather low D-max, compared to D19, the later being my usual developer for testing purposes.
    I am not sure that this means anything at all concerning the topic at hand. Just an observation.
    Cheers,
    Bill

  9. #19

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    Sorry,
    I left out a phrase. I meant to say-After washing the polymer and lowering the pH with H2SOS, I was still unable to re-disolve the polymer, regardless of heat.

  10. #20
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    Bill;

    Try ultrafiltration for washing. You don't need acid or base, just a filter and a pump. The setup is shown in both my book and the DVD in disk #2.

    PE

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