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  1. #21
    keithwms's Avatar
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    My shipping address is Keith Williams, UVA Physics, 382 McCormick Road, Charlottesville VA 22904. Sample size... well I can do very small samples if desired. I was planning to use ordinary microscope coverslips cut into ~1x1" squares. 1mL would easily coat that, many times over.

    Question is whether you want me to test exposure, or you... I could do simple tests.

    Wish I had some blank plates for my rb, it has plate holders for that, let me see what I can come up with....

    The big advantage of spin coating is that it is extremely economical in material. Whatever your emulsion costs, I can tell you that some of the resist I use are far more costly. And unused material can actually be recovered... partially at least.

    I suppose now would be a good time to mention that I am also looking into adapting an inkjet for paper coating...
    "Only dead fish follow the stream"

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  2. #22
    Photo Engineer's Avatar
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    Keith;

    I would like to remind you that the dry layer should be about 10 - 100 microns depending on emulsion which means that the emulsion itself must be put down at about 5 - 7 mils thickness. Can you do that? Resists are put down much thinner.

    PE

  3. #23
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    I can't promise Ron, but I can certainly try, and in the worst case, multilayer spinning is not difficult.

    Regarding typical thicknesses, I wonder if that's really a necessity or if that's just what the bulk coaters can do best....
    "Only dead fish follow the stream"

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  4. #24

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    Keif,
    My newwest batch is 0.25 M, based on the MW of AgNO3. Would 100 grams be enough to do all the tesing you would like to do?.
    I will supply it in a light-proof container. Refridgeration is not required.. It is a blue sensitive emulsion in its current form. My "standard" developer is undiluted Kodak D19 for 8.5 minutes..
    I do not have any glass plates that would fit your coating machine, as my usual plate size is 5"X7". Maybe someone who is sending you a sample could send you some 4"X5" plates. I think that your amber safe lights should suffice for this emulsion.
    I am quite excited about this emulsion because, even with extended soaks in developer, it shows no signe of fogging.
    I will get this off to you tomorow, Thurday.
    Many thanks for your intrest and desire to help,
    Bill

  5. #25
    keithwms's Avatar
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    Cool Bill, I look forward to seeing whether it works. Yes, 100 gr is probably, what, 25-50mL? Should be plenty. I can get some plates, no worries.
    "Only dead fish follow the stream"

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  6. #26

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    Regarding minimum thickness, I think that this might be , in part, developer dependant. With my emulsions, D19 yields deep black highlight areas. Pyro on the other hand yielss week browns.

  7. #27
    keithwms's Avatar
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    Yep I guess the thing to do is a wedge-like test and just see what provides optimal contrast. But first things first, let's get some on some glass!
    "Only dead fish follow the stream"

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  8. #28
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    Keith;

    The thickness is based on concentration and being able to get Dmax. If you coat too little you can't get Dmax. And, this is based on how much one can actually make the emulsion capable to do this.

    PE

  9. #29

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    Quote Originally Posted by Photo Engineer View Post
    Keith;

    I would like to remind you that the dry layer should be about 10 - 100 microns depending on emulsion which means that the emulsion itself must be put down at about 5 - 7 mils thickness. Can you do that? Resists are put down much thinner.

    PE
    I guess coating speed for gelatin AgX emulsions needs to be pretty low.

    In the context of holography spin coating has been widely used - both for preparing photoresist layers for embossing and the making of holographic optical elements (HOE) mainly. Richard Rallison, one of the pioneers of DCG, put a couple of papers online that explicitly dealt with spin coating. After this passing they are no longer available.

    In his paper, Control of DCG and non silver holographic materials (SPIE 1600, 1992), he wrote:

    A variable speed turntable capable of 50 to 100 RPM will coat films of gelatin or PVK from 4 to 50 microns on 8 x 10 inch glass or plastic substrates. Plates as small as 3 inch diameter or as large as 16 x16 inches have also been successfully coated with this range and technique. The turntable should be equipped with a surface or arms that will mate to a removable tray that is one or two inches larger than the substrates being coated. We have used ordinary variable speed phonograph players with pie tins turned upside down and glued to the turntables and we have used Dayton variable speed gear motors with heavy duty arms attaches. Both devices worked very well.

    Trays have been made up of stainless steel, plexiglass, polyethylene dishpans or modified from aluminum cake and pizza pans. The best trays have straight sides measuring 2 1/2 to 4 inches high and are fitted with 3 rubber posts inside and outside. The posts inside hold the substrate an inch or so off the bottom of the tray and the outside posts serve to level the tray during pouring of solutions and to center the tray during spinning. The spinning tray and substrate may generate useful turbulence that aids in drying and distributing the solution. Excess solution is caught in the tray and emptied between substrates then is easily soaked clean in hot water after a days activities.

    An important component that augments drying and uniformity is the blower-heater. It hangs off center and above the whirling tray. Turbulence and heat combine to make uniform coatings in about five minutes. We recommend the use of a variable temperature 600 watt blower such as might be found in the ceilings of some bathrooms. A little experimenting with angle and position will quickly determine the best place to hang this unit in your clean hood or bench area. Coat and examine uniformity by looking for local fringe patterns under a fluorescent lamp or better yet a fluorescent long wave black light.

  10. #30
    keithwms's Avatar
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    I do have a hair blower

    I can do low speeds, of course. I suspect that the best result will be for a combination. Maybe one cycle high speed to get an initial wetting layer, and then slow, and then a little bake to even things out.
    "Only dead fish follow the stream"

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