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  1. #31

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    [ there is a "newer" way to develop a daguerrotype plate which does not require Mercury. The plate after exposure is exposed to sunlight behind a red filter ( I think the specific color is very important to the process) and it develops the plate.


    Hi,
    That is the process taught once per summer in Montana. The best of these look animic beside a traditional Dag.
    Bill

  2. #32
    greybeard's Avatar
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    A couple of odd bits of chemistry related to posts above:

    Wasabi is a member of the mustard family of plants (Brassicaceae). In the early days of silver-gelatin technology, variability in emulsion speed was traced to the gelatin, some of which came from cows that had grazed on wild mustard. (Life in the Kodak research labs must have been very interesting in those days.) The family of sulfur compounds that give overcooked cabbage its bad reputation contains the ones that react with silver in the emulsion. So, wasabi is probably not useful as a developer per se but might replace mercury as a hypersensitizer!

    Regarding the use of vacuum to speed up mercury development of a daguerrotype: the vapor pressure of mercury is only a function of temperature, so reducing the air pressure does not increase the mercury concentration. What it does do is to greatly increase the transport rate from the liquid through the vapor space to the plate, since the air molecules are no longer in the way. Similarly, putting air back into the chamber will not magically condense the mercury; it will just dilute whatever concentration of mercury vapor that was there into a larger volume of air, so you still have the breathing hazard. Sorry about that...

  3. #33
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    Beard;

    The actual compound in mustards is / was, allyl thiourea. By refining it out we have modern inert photographic gelatins and the sensizier is now either Sodium Thiosulfate or Sodium Thiocyanate which act by decomposing and forming Silver Sulfide. This is not the same as the action of Mercury.

    Mercury is also an antifoggant under some conditions, and a preservative under others.

    PE

  4. #34

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    Quote Originally Posted by Ray Rogers View Post
    Sorry - I did not meant to hijack...

    The wasabi maybe related more to emulsion making than processing.
    I doubt there is anything on the net as the research is unpublished.

    Yes the pasta is very popular here.

    Ray
    My apologies - I did not mean to infer that you Hijacked the thread, but rather that I did. An interesting point that Wasabi might work as a sensitizer. it is green after all - think it might sensitize an emulsion to red light?

  5. #35

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    Quote Originally Posted by totalamateur View Post
    My apologies - I did not mean to infer that you Hijacked the thread, but rather that I did. An interesting point that Wasabi might work as a sensitizer. it is green after all - think it might sensitize an emulsion to red light?
    Speculating... I would have to say...
    Yes, actually!
    But way too weak to be of practical use as a color sensitser.

    This stuff can be really the opposite of clear cut.
    The same chemicals frequently act in very different ways depending upon concentration, stage of process, temperature, environment... phase of the moon and one's horroscope.

    Ray
    Last edited by Ray Rogers; 09-04-2009 at 01:52 PM. Click to view previous post history.

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