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  1. #111
    holmburgers's Avatar
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    Quote Originally Posted by T-grain View Post
    IF we replace sucrose with sorbitol, thymol with, say benzoate (or something similar), the tissue with dichromate should be stable for a long time, provided it is kept away from UV light. Correct?
    I don't think there's any cause to believe this would be the case.

    Now, do I have hard facts to back this up? No.. but people have been carbon printing for going on 2 centuries (minus 40 years let's say) and although there's always the possibility of new discovery, I'd say that this one has been hashed out over and over again. In the literature there is information regarding extension of the shelf-life of sensitized tissues, but nothing that could compare to diazo/azido sensitizers.
    If you are the big tree, we are the small axe

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    PE, you refer to silver halide emulsions, I guess?
    maybe with dichromate or diazo stuff it would be another story

    BTW, how is going your work with mordanting the dye in your dye-destruction (cibachrome) emulsions? last time I followed your posts, you said you tried with aluminum salts

  3. #113
    Photo Engineer's Avatar
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    No salt I have used is a good mordant. I will have to move to quaternary salts to get the results I desire. I have one at the present time that I plan on trying and I have some other avenues to pursue. But, I have been busy and this is a difficult and off-topic (for me) piece of work. I have also not found a good cyan dye.

    PE

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    Quote Originally Posted by holmburgers View Post
    I don't think there's any cause to believe this would be the case.

    Now, do I have hard facts to back this up? No.. but people have been carbon printing for going on 2 centuries (minus 40 years let's say) and although there's always the possibility of new discovery, I'd say that this one has been hashed out over and over again. In the literature there is information regarding extension of the shelf-life of sensitized tissues, but nothing that could compare to diazo/azido sensitizers.
    Chris, you're probably right (I never did a dig-in into carbon literature), but diazo sensitizers are probably not the only factor influencing the shelf life of ultrastable material
    as a chemist I can tell dichromate solutions are VERY stable when kept in the bottle (in the dark of course)- we used to use dichromate for spectrophotometer calibration
    I do not have the redox potentials here at hand (they are also pH dependent), but I cannot exclude glucose from reducing dichromate ions

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    Quote Originally Posted by Photo Engineer View Post
    No salt I have used is a good mordant. I will have to move to quaternary salts to get the results I desire. I have one at the present time that I plan on trying and I have some other avenues to pursue. But, I have been busy and this is a difficult and off-topic (for me) piece of work. I have also not found a good cyan dye.

    PE
    we have faith in you, PE

  6. #116
    holmburgers's Avatar
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    Quote Originally Posted by T-grain View Post
    as a chemist I can tell dichromate solutions are VERY stable when kept in the bottle (in the dark of course)
    That's a good point actually.

    The key is keeping it away from oxidizers, right?, so any organic material? But that would preclude the use of gelatin also.
    If you are the big tree, we are the small axe

  7. #117
    Photo Engineer's Avatar
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    Dicrhomate is an oxidizer. You want to keep it away from reducing agents.

    PE

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    Quote Originally Posted by CMB View Post
    1. Add 1.5 g of Hardener #3 to 50 ml of water at 85F and QS to 60ml.
    Charles,

    Maybe a stupid question (from a non english reader) but what do you mean with 'QS to 60ml'?

    Kees

  9. #119
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    Quote Originally Posted by Photo Engineer View Post
    Dicrhomate is an oxidizer. You want to keep it away from reducing agents.

    PE
    Just looked up "redox" reaction... I get it now!

  10. #120
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    Quote Originally Posted by keesbran View Post
    ...what do you mean with 'QS to 60ml'?

    Kees
    Q.S. (quantity sufficient) means add solvent to bring the total volume to:



 

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