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  1. #11

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    I'm getting there...

    I had a good long session this weekend and think I've cracked it!

    I tried all of the suggestions various people made and also changed the dilution (i.e. the %age of gelatine) but started with 100ml plain distilled water in which I dissolve just 10g of gekatine and nothing else. This coated much the same as my original dummy emulsion with the food colouring etc. added. This proved at least that the additives were not the cause of my difficulty.

    I then went through all of the suggestions one at a time, adding to this first batch of gelatine. Rather than do everything at once, I wanted to see if there was a 'Eureka' moment. There wasn't, really.

    I won't detail everything here as the post will be too long. In a nutshell:

    Alcohol and photoflo helped a lot.
    So did keeping the emulsion at 40 degrees.
    Diluting the emulsion to 7.5% gelatine made the biggest improvement.

    Plate cleanliness wasn't my problem.
    Breathing on the plate and warming the plate to 40 degrees made the emulsion flow more easily, but also made it run off the edges much easier, too! I managed better without these steps (Room temp was about 25' C anyway).

    I think my problem was my first dummy emulsion was too viscous. It flowed badly and set far too thick. The 7.5% version with the alcohol and photoflow at 40 degrees C flowed much better and I was able to coat a dozen plates very well and they set with a nice thin, hard and even coat. I'm sure the fact that I've coated about 50 plates now has helped, too.

    Now, to see if I can repeat this with a real emulsion...
    Steve

  2. #12
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    Excellent news! hope it goes as well with the real stuff!
    How big are your plates and how much emulsion are you pouring?
    Lens caps and cable releases can become invisible at will. :D

  3. #13

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    Quote Originally Posted by ben-s View Post
    Excellent news! hope it goes as well with the real stuff!
    How big are your plates and how much emulsion are you pouring?
    Hi Ben,

    I'm using a mixture of quarter plates and 3 1/2 X 2 1/2 plates - so pretty small. I don't know how much emulsion is needed for each plate. I haven't measured it yet because my last attempt involved so much adding and diluting it was to difficult to tell. I guess I'm pouring about 8ml on a 1/4 plate and returnng about 4ml to the pouring vessel, but that's just a guess. What I do know is that 100ml of emulsion goes a long way - it would do dozens of the smaller plates. Maybe my next step (since I have a lot of my latest 'dummy' emulsion left) will be to coat another batch and measure how much I use.

    Steve
    Steve

  4. #14
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    Steve;

    Remember that a 10% real emulsion will have a viscosity more like an 8% pure gelatin solution. This is the peptizing interaction of the emulsion with gelatin and depends a lot on the type of emulsion as well.

    I use about 4 ml to coat a 4x5 with a measured coating gap of 0.005 - 0.007 inches. You will have to use more to get that same thickness as you are pouring it on, but 4 ml is a ballpark of actual use. I believe that you will need at least 6 - 12 ml to achieve that and you will recover the excess.

    PE

  5. #15

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    Quote Originally Posted by Photo Engineer View Post
    Steve;

    Remember that a 10% real emulsion will have a viscosity more like an 8% pure gelatin solution. This is the peptizing interaction of the emulsion with gelatin and depends a lot on the type of emulsion as well.

    I use about 4 ml to coat a 4x5 with a measured coating gap of 0.005 - 0.007 inches. You will have to use more to get that same thickness as you are pouring it on, but 4 ml is a ballpark of actual use. I believe that you will need at least 6 - 12 ml to achieve that and you will recover the excess.

    PE
    Hi PE,

    Hopefully this should work out ok as my real formula is a bit higher in gelatine than my 7.5% dummy, but I think I could adjust the alcohol and photo-flo to get what I now know I need it to flow like. Ill find out this weekend

    Steve
    Steve

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