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  1. #91
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    Yes, Chris. Email sent to himself!

    PE

  2. #92
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    And the answer is:

    Any sensitizing dye will sensitize an emulsion wherever it has a peak. This does not have to occur at 1/2 Lambda max.

    PE

  3. #93

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    PE,
    To skip to another question on dye sensitization: Using dyes such as SDA3057, which are added at the end of the make. Once a dye has been sufficiently mixed, such that the dye has coated the silver-halide crystals, would washing wash out the dyes, or are they sufficiently bonded to the halide to withstand washing. I am thinking that this might be a way to optimize dye concentration and eliminate excessive dye. Of course, I could take a very small amount of dye sensitized emulsion and try it. But I hate to waste emulsion, if you already know the answere..
    Bill

  4. #94
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    Quote Originally Posted by BobCrowley View Post
    When I saw the UV/blue response at 1/2 lambda of the IR films, I thought there had to be either harmonic doubling, or instrument artifact.
    I suspect maybe the blue/UV sensitivity is merely the native sensitivity of the emulsion, without dyes. The dye absorbs in the IR region and emits in the Blue/UV region, giving the IR sensitivity but retaining the original sensitivity.

  5. #95

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    The two blue peaks are quite pronounced and are at lambda/2. So this is actual response, and not an instrument artifact? Also, apparently a strong, broad absorber in the sensitizing target region has to do more than absorb, it has to exchange electrons with adjacent halides. Any absorber can produce something, like heat, but others are better at charge transfer to an adjacent molecule. Does that require a chemical bond?

  6. #96
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    Bob;

    Remember that sensitizing dyes are also desnsitizers in the blue region and you can use enough such that the blue speed is strongly repressed. They are also, in some cases, development inhibitors.

    Bill;

    Yes, you can wash off excess dye, but that is NOT the way to go. You should do a dye series and then coat and test and pick the best level. Otherwise you introduce another variable.

    PE

  7. #97

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    Quote Originally Posted by BobCrowley View Post
    The two blue peaks are quite pronounced and are at lambda/2.
    If a diffraction grating is used in the design of a recording spectrograph, then care does have to be taken to eliminate 2nd order diffractions so that they do not show up when trying to measure a 1st order diffration. The second order pattern will be at 1/2 the wavelength of the 1st order, and when trying to record wide ranges of wavelengths, it can be a big problem.

    It's not an issue if a prism is used.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  8. #98

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    Here's a nice article on absorption of a cyanine dye and how it can be solved using Schroedinger's wave equation (the particle in a box analogy).
    http://www.dartmouth.edu/~chemlab/ch...chemistry.html
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  9. #99

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    PE,
    Would not a wahing of a pigmented emulsion be a more accurate way of eliminating excess pigment, as grain size may vary somewhat from batch to batch, regardless of how much care is given to temperature and rate off adition of Ag, and all that factors that influence grain size.Assumung one is not using an automated programed system? What if I were to hold off all washing untill the pigment had been added and dispersed? Could the same process be used for Au and S sensitization.
    I do not want to sound stuborn here. But I want to make sure that this is a bad idea befor I abandone it completely.
    Bill

  10. #100
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    Well, lets firsts not call the dyes pigments as they are entirely different, especially here and it can confuse casual readers.

    Now, as to the question, the dyes adsorb at their preferred ratio if you add them to the emulsion. Since you stir, the dye is distributed and used up at the proper amount for each grain size. It is only when you have too much that the situation is as you describe. If you do a proper series, you see this actually take place.

    And, I would add that your method would work if there was an excess of dye, but you would also change the vAg of the emulsion thereby changing its surface adsorption characteristics. It would therefor cause some sort of secondary problem IMHO.

    PE



 

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