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  1. #111
    kb3lms's Avatar
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    No, that would never be any fun! I have glyoxal now as well as sorbitol, so some different things to try. Also picked up some Everclear, which is available in Maryland. Now all I need is some time.

    Chris, is your coating on wet-media Dura-lar still holding?
    All this has happened before, and all this will happen again.

  2. #112
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    Amazingly, yes!

    Even on cut edges and without sorbitol, there appears to be no signs of delamination or peeling. I'm skeptical... I think it's a trick.. as soon as I coat something important, it will peel!

    I'd encourage you to experiment with this wet-media stuff though, so we can say with confidence that it works.

    In the meantime, I'm trying to think of some ways that I can stress the coatings to really see how good they're holding. Any ideas?
    If you are the big tree, we are the small axe

  3. #113
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    Chris,

    I will get a pad of 5ml wet media dura-lar. Got in this far, might as well try one more! The NaOH treatment definitely works but if we can get rid of it, so much the better. Another thing I think that might have something to do with stripping and frilling is pH of the NaOH solution. The last sheets I prepped I tried using a 1.0M NaOH solution rather than 2.5M. After processing a few sheets, I didn't think it was doing a great job and on a hunch I checked the pH which IIRC was around 11.7. NaOH should be higher than that, I think. Possibly the terepthalic acid and ethylene glycol are lowering the pH. After the NaOH sat in its jug over the 1 1/2 weeks since going on vacation, I now note a layer of grey powder or crystals on the bottom of the jug. I'm guessing this is terepthalic acid.

    WRT stressing the coatings, yes.

    1) Soak in an alkaline solution such as your favorite developer and see how long it lasts. At cut edges the water seems to work in an under the gelatin is adhesion is not good. This test is mine.

    2) The scotch tape test: Take an x-acto knife (or similar, but razor sharp) and a ruler and cut across the gelatin. Cut through the gelatin but not the base. Attach a piece of tape, say 2 inches long, across the cut. Carefully pull up the tape to the cut, then rip up the rest of the tape as fast as possible. The amount of emulsion that peels off tells you how well it sticks. No peeling is obviously best. This came from a Kodak patent.

    3) Wet stripping test: See US Patent 2014547, Babcock ass. Kodak, 9/17/35 Page 3. There is also a dry stripping test given but PET will not tear in the same way.

    If you search some of the patent literature on subbing from the mid-1930s through the mid-1950s you can find a number of different tests. Kodak patents seem to have given the best information.

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

  4. #114
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    Jason, those are fantastic test ideas; thank you very much!

    Here's the test from patent 2,014,547:

    The stripping test usually comprises two parts, namely, dry stripping and wet stripping. The wet stripping test is carried out as follows: A strip of the emulsion coated film of convenient size, say 6 to 40 inches, is soaked in water at 70°F for ten minutes. It is then removed from the water and fixed on a flat surface with the emulsion side up. The emulsion is then gouged or creased with the finger nails at points near the middle and end of the strip. Each nail scratch tears the emulsion away from the support to a certain extent. The scratched places are then rubbed with considerable force with the balls of the finger tips for several seconds. A film is said to have satisfactory wet stripping (emulsion adherence) properties when no peeling, or substantially no peeling, of the emulsion occurs as a result of this rubbing action. Wet stripping is said to be unsatisfactory when an appreciable or large amount of the emulsion comes off. For most types of film it should not be possible thus to remove pieces wider than 1/4 inch by this test.

    Is the terphthalic acid coming from the PET and "poisoning" your NaOH subbing bath? What about the ethylene glycol, where does that come from? It's a very clever theory, and seems like a good explanation if you're discovering that the peeling sheets are those which were treated in this potentially compromised bath.

    Unfortunately my coatings have no hardener in them, so I might have to harden them or lower the temp° of any wet tests.
    If you are the big tree, we are the small axe

  5. #115
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    Chris,

    The PET, or poly(ethylene) terepthalate, is made by the estrification terepthalic acid ethylene gylcol. By soaking the PET in the NaOH solution with some heat, the PET is subjected to saponification (base hydrolysis of an ester) which breaks the PET down into the salt of the carboxylic acid (terepthalic acid) and the alcohol (ethylene glycol) that formed it.

    Terepthalic acid is a colorless solid with very low solubility in water, so it makes sense that it would have settled out. Ethylene glycol is miscible in water, so it's in solution. Because of the hydrolysis the solution starts going bad from the moment you start using it. However, hardware store lye is cheap. And I suppose it cleans out your drain somewhat when you dump it.

    I'm on the edge of my chemistry so if I have this all wrong, please jump in and correct me. Anyway, unfortunately I did not check the pH of the 1M NaOH solution before I started. So maybe it's the acid, or the ethylene glycol, or my solution is defective, not really sure.

    At the moment, I am fooling with an alternative process that looks even more promising. Or it might be a bust!

    More to come.

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

  6. #116
    kb3lms's Avatar
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    Even on cut edges and without sorbitol, there appears to be no signs of delamination or peeling. I'm skeptical... I think it's a trick.. as soon as I coat something important, it will peel!
    Chris, put it through some developer and see what happens. The Melinex 535 and the 3M product do not seem to require any sugar alcohol or hardener. IDK if it would work better with those additives.

    On another note, the other night I processed some Tri-X in the same plastic tub I used for washing the NaOH treated PET. This was a mistake! PE told me that NaOH was a foggant and I believe that some residual NaOH in the tub got into the water and messed up the Tri-X. Now I haven't used Tri-X in a long time and never in 120, but I don't remember it having a purple frosted base. Fortunately the negs are not important and look usable but word of caution, the NaOH seems t work itself into some plastics and is a b%&$h to get out!

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

  7. #117
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    Jason;

    You have the saponification correct above. However, some of the PET will be partially saponified and the phthalic acid in this case will be attached on one side to the ethylene glycol and the other end will be free to grab gelatin. This is a very efficient way to create the adhesion we want. OTOH, you have to remember that in all of these methods a thin layer of PET is destroyed. The choice then is to choose the least harmful method.

    In the case of NaOH, didn't you mean NH4OH? Sodium Hydroxide in excess will cause extremely rapid development that leads to fog, but alone it does not cause fog. In fact, I doubt if there was enough residue in your tub to cause any problem at all. NaOH washes out very rapidly and completely with just several changes of water.

    PE

  8. #118
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    Jason,

    Thank you for the "heads-up!" to avoid using the same plastic containers to both sub with NaOH and process film. It makes perfect sense that anything that is strong enough to alter PET would hard-to-impossible to clear from the plastic. NaOH does indeed fog emulsion. (See post #90.) Traditionally, that implys its use in developers, but use is use.

    Excellent work! I've got my fingers crossed tight for you. Although 3M assures me (and I believe them) there will always be PET film subbed for hydrophilic coatings, it's always cool to be able to go DIY all the way. Do you think you'll need to deal with any residual NaOH in the subbing? Perhaps a coating of plain gelatin (or maybe a bit of added acid?) between the subbed PET and the emulsion? Again, really cool stuff. Congrats! Also, I'm trying to pull together everything I can find on the ins and outs, ups and downs of gelatin with a new section on TLF: http://thelightfarm.com/Map/Gelatine/GelatinePart1.htm (It's a work in progress, but can't that be said for everything )

    Thumbs up!
    d
    www.thelightfarm.com
    Dedicated to Handmade Silver Gelatin Paper, Film, and Dry Plates.

  9. #119
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    Let me clarify that post.

    Strong base can affect raw emulsion during coating and drying due to pH shifts and the low (relatively) water content of the emulsion during coating. Therefore, if the surface pH of the substrate is alkaline, the emulsion may be fogged.

    But, if you have a strong base in a developer, the effect is much lower and it can be used there safely. Many developers contain very strong bases. However, the strong bases give high activity and if this is not controlled you can get fog there too.

    So, as a summary, you should coat at pH 5.5 to 7 for best results. Above that and you can induce fog and this happens in the presence of strong base. Ammonium Hydroxide is even worse due to its solvent effects. Strong base can be used in developers with no serious problem except their high activity. This can lead to fog.

    PE

  10. #120
    kb3lms's Avatar
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    PE, next time I coat I will check the pH of my emulsion. If it is too high, what is best to use to lower it?
    All this has happened before, and all this will happen again.



 

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