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  1. #81

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    Actually, the Melinex from the Formulary has an anti-static coating on the back side.

    Regards - Jim

  2. #82
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    Dura-Lar

    This past week I ordered a tablet of 5 mil Graphix Dura-Lar sheets. Dura-lar (DL) is Graphix's brand of PET film. Last night I gave the DL an overnight soak in a 10% NaOH solution and I am happy to report that it worked at least as well as the PET cut out of the tomato container. Water beads like crazy on the untreated DL and spreads out and just sits nicely on the treated DL. Also, the DL did not become cloudy in it's overnight bath. Tonight, I plan to mix a batch of subbing solution and try subbing the DL.

    Question about Subbing
    When it is said that gelatin disperses in acid, does that mean that it doesn't gel? For example, if I swell gelatin and melt in 5% vinegar, it does not gel at room temperature anyway. That's what is meant by dispersion?

    -- Jason
    All this has happened before, and all this will happen again.

  3. #83
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    The context of your question is unclear. However, you can melt gelatin in acid as well as water so you end up with gelatin in hot (or warm) acid or water depending on what you want. Gelatin will gel below 20 deg C or 68 F even in acid. However, extremely strong acid denatures gelatin and prohibits gelation. This gelatin is considered useless for most purposes as it can be easily washed away.

    PE

  4. #84
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    Hi PE, patents and other literature regarding subbing discuss gelatin dispersing in weak acids. For example, from US Patent 2461475, Kaszuba et al:

    Page 1, paragraph 2 (I'm editing this a little for brevity)
    ... Since hardened gelatin, as used for glass plates does not adhere to a film base, it is necessary to use a mixture of gelatin with an organic solvent for the material of the film base, such as acetone .... or an alcohol/acetone mixture. Gelatin is insoluble in these organic solvents and the film base is insoluble in water, but it is possible to prepare dispersions consisting of gelatin in a mixture of one of the organic solvents and water with a volatile organic acid, such as acetic acid ... as a dispersing agent.
    The rest of this patent goes on to discuss the idea of using ascorbic acid rather than acetic acid as the dispersing agent. I recently reread this patent and I don't think I am clear in what they mean by dispersion. Since acid serves to desensitize an emulsion, what role is played by the acid? Why not just swell and melt gelatin in water, then add to an acetone and methanol mixture?

    Typically an 8% or so gelatin - water mixture sitting on the shelf in my darkroom at room temperature (about 70F) will gel after a few hours. The gelatin - vinegar mixture does not.

    By the way, the subbing solution discussed in the patent does actually work on CTA but its very finicky to make. If you aren't careful and have the methanol at the right temperature, you get a white, sticky glop in the bottom of your container.

    -- Jason
    All this has happened before, and all this will happen again.

  5. #85
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    A possible winner!

    Results of first coating tests with PET are in. I coated NaOH prepared test strips (10% solution) from the veggie container PET and Dura-lar with an 8% gelatin with red food dye added. Other than the NaOH treatment, there was no additional subbing done.

    Coating was simple, I just dipped the strips in the container of gelatin and made sure to coat both the treated and untreated part of the strip. This was straight gelatin - no hardener or anything. After drying, the strips were suspended in 68 F water for 10 minutes. Gelatin on the treated part of the strip stayed put. On the untreated part the gelatin showed frilling. (I would hazard a guess that gelatin on the treated part of the strip was holding it in place.) No observable red dye in the water.

    This has been my standard test and showed failure of the PVC and acetate base in the past and success of the CTA, melinex and 3M films. If the gelatin stayed put on the PET, I have some confidence it will work.

    Time to get more serious. If I have time tomorrow I think I will melt some emulsion and try this for real.
    All this has happened before, and all this will happen again.

  6. #86
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    Great!

    How can this be so simple?

    If the answer really is just to bath in some NaOH, then there is no reason for a hobbyist to try create corona treatment, or to buy ready-subbed materials more expensive and harder to find.

    Well, it makes sense that this has not been described before; in an continuous industrial process, very long chemical soaks are not feasible. But for us and our sheets, it does not matter at all.

    Now we only need a test with a real emulsion. Water beading test is the first step, coating gelatin with coloring and testing in water is a better one, but a silver gelatin emulsion may behave differently still. I had a case when I was testing acetate subbing formula that it worked for test coating with gelatin and color, "developed" in solution of sodium carbonate for 10 minutes or so, but it didn't work with real emulsion at all.

    I have fingers crossed here that your test with real emulsion works. Good luck!

  7. #87
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    Jason;

    The method described in the patent is one that has been known for years. Many authors such as Wall and Baker disclose subbing layers with gelatin in acetic acid and an organic solvent. If the gelatin does not fully dissolve, it can form a milky liquid which can be termed a dispersion. A dispersion is a mixture of a liquid and a solid, where the solid does not precipitate.

    http://en.wikipedia.org/wiki/Dispersion_%28chemistry%29

    However, in photography, the terms dispersion and emulsion have become corrupt and are reversed and thus a dispersion may be an emulsion. It is hard to say.

    http://en.wikipedia.org/wiki/Emulsion

    These references are to the classic definitions of the two. If you reverse them then it is the photographic definition and this came about because the early workers either did not know what they had, or were not aware of the definitions.

    In any event, I suspect you are discussing a classic mixture of two liquid materials which do not dissolve, and which form a single phase of one material with small droplets of the other material suspended in it. I will not use a classic term here due to possible confusion.

    It is sufficient to say that this method has been used for over 100 years, and that Kaszuba must have claimed something unique.

    I am glad that the Sodium Hydroxide method worked. Please take care as that solution is very strong and very dangerous. It could take the hide off of an elephant with no trouble at all. Use safety goggles when you use it and don't get any in your eyes.

    PE

  8. #88
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    Now we only need a test with a real emulsion. Water beading test is the first step, coating gelatin with coloring and testing in water is a better one, but a silver gelatin emulsion may behave differently still. I had a case when I was testing acetate subbing formula that it worked for test coating with gelatin and color, "developed" in solution of sodium carbonate for 10 minutes or so, but it didn't work with real emulsion at all.
    Yeah, been there, done that! I've got a full sheet of Dura-lar soaking now.


    PE, you bet! I have no desire to lose my hide!
    Last edited by kb3lms; 06-24-2012 at 12:16 PM. Click to view previous post history.
    All this has happened before, and all this will happen again.

  9. #89
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    Test #1 with emulsion

    Test #1 has given a mixed bag. For this test, I melted a small amount (10 ml) of emulsion and coated a test strip by dipping - same as the plain gelatin. After about 90 minutes drying at room temperature, a bath in stock XTOL for 10 minutes caused frilling. Now on the untreated part of the strip, the emulsion adherence was nil, on the treated part there was frilling but the emulsion in the center stayed firmly in place. I don't think the emulsion was fully dried and hardened yet.

    Some other variables in the mix: 1) I forgot the hardener (3% chrome alum) again(!) and 2) the strip was rinsed in photo-flo water rather than just plain water prior to coating.

    I have another strip coated and ready to test. The second one was only rinsed in plain water, was given a dip in a chrome alum bath for hardening and I plan to leave this one sit on my desk and fully harden overnight before testing.

    Looking at the coating on the photo-flo rinsed vs non-photo-flo rinsed right after coating, I would say the strip not rinsed in photo-flo gave a nicer, more even coating. For now, I plan to avoid photo-flo and stick with plain water for future tests.
    All this has happened before, and all this will happen again.

  10. #90
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    Check for fogging in the coatings with the NaOH treatment. Strong base can affect emulsions.

    PE

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