Quite a good coating on acetate

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by hrst, Apr 22, 2010.

  1. hrst

    hrst Member

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    Inspired by Denise's success on subbing and coating celluloid diacetate sheet, I made a quick experiment and succeeded quite well and quite easily.

    I ordered a 0.005" diacetate roll from dickblick.com.

    I made a subbing from gelatine, acetic acid, methanol and acetone. I took some random piece of cloth and gently wiped the acetate sheet with the cloth using a squeegee. The problem was that the subbing made sheet wrinkle somewhat, making proper coating impossible with our blade.

    Then, a second try; I sprinkled some water to a clean glass plate, put the acetate sheet on top and then carefully squeegeed the sheet to the glass (trying to get rid of all air bubbles) and secured the corners with masking tape. This was quite easy and guarantees the flatness throughout the rest of the process.

    Then I wiped the subbing layer on the sheet. Some minor streaking occur at this stage, but this really doesn't seem to be visible in the final scan after coating.

    I let the subbing layer dry for 15 minutes and made a test "emulsion";
    17 g hot tap water
    2.0 g gelatin (PIG food grade, of course! :wink: )
    1.0 g glyoxal 4%
    5 drops Agepon
    A tad of erythrosine

    And coated with a blade set at about 300 um gap.

    Then I let it dry and harden for 2 days.

    It remained perfectly flat on the glass plate for the whole time while drying, but curled somewhat after removed from the glass.

    I cut a 60mm wide test stripe with a box cutter and "processed" it at 24C:
    1% sodium carbonate for 10 minutes with almost vigorous agitation
    1% acetic acid for 3 minutes
    Wash for 5 minutes
    Final rinse with Agepon for 1 minute
    Dry in warm air.

    It survived!! Totally different from our results with unsubbed PET, which started flaking at the borders after 1 minute and was completely loosened after 5 minutes or so.

    The only real problem seems to be that cutting the film causes emulsion cracks at the borders. Emulsion is very "hard" in this sense. The curling is also heavy and more force is needed to lay it flat than with any real film. I think adding sorbitol will solve these problems well enough for us. I think the pig gelatin is not the best one in this sense.

    The emulsion flakes of at the cut borders where the emulsion has cracked, but now the adhesion is strong enough so that the flaking remains only at the cracked site, not spreading at all.

    Attachment: a scan of the "processed" and dried 60mm wide strip. Darker spots may be erythrosine spots because I added it just before coating. Or they may be air bubbles or dust.... Better cleaniness next time!

    I think we are ready to go for a next real emulsion.
     

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    Last edited by a moderator: Apr 22, 2010
  2. Kirk Keyes

    Kirk Keyes Member

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    That looks pretty nice! I'm looking forward to seeing some photos with your new technique!

    Perhaps less glyoxal would produce an emulsion that doesn't crack during cutting?
     
  3. hrst

    hrst Member

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    Now that's a good idea! I didn't even think about it, just adding sorbitol as plasticizer, but indeed less hardening could be good. More hardening improved the results with unsubbed PET as it reduced swelling that finally loosened the emulsion as its size changed compared to base. But, indeed, less hardening could improve even the adhesion because it gets more flexible just like the acetate base is much more flexible than PET. The optimum might be somewhere in halfway.

    I also suppose that 30 um is quite a thick emulsion for a BW film. Right? Thinner emulsion would also reduce curling, which is a major problem now. Scanning is impossible with most scanners and their lousy holders now.
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    Very nice work.

    Sorbitol will help prevent cracking.

    Coating a gelatin backing on the film will help reduce curl.

    PE
     
  5. hrst

    hrst Member

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    Oh, that's a good idea. Thank you. I could also add some black or dark dye that washes away (a small molecule?) to that backing to make it an anti-halo backing, right?
     
  6. Photo Engineer

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    There are special dyes for that. I can look them up. But, basically, yes.

    PE
     
  7. dwross

    dwross Subscriber

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    Great looking R&D, hrst.

    Couple of points: A plain gelatin backing probably won't work as an anti-curl layer. I think it will peel right off before processing, although it's possible it might last until that stage. You should consider applying your subbing solution to both sides. Literature suggests that erythrosine in the back subbing will work well to cut down halation. I don't see how you can incorporate a black or dark dye unless you know of one that will chemically clear during processing. It won't physically wash out in processing and will then interfere during printing. If you were coating glass, it would be a different story. Any backing applied to the plate before the emulsion coating step can be easily removed. Gelatin with burnt sienna pigment or ivory sienna black was a favored technique.

    Also, I don't use a hardener in any of my negative emulsions, glass or film. Never had a problem.

    d
     
  8. Photo Engineer

    Photo Engineer Subscriber

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    This is diacetate, not Estar or something like that.

    In this case you can use the same basic subbing on both sides and then put a gelatin anticurl layer on one side and the emulsion on the other. You could do the same to Estar by bombarding both sides and coating a subbing on each side after bombardment. If done correctly, it will not come off.

    PE
     
  9. hrst

    hrst Member

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    Erythrosine doesn't seem to wash away from gelatin so it would affect printing severely. And yes, subbing layer would be needed for the backing, too.
     
  10. Photo Engineer

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    Done correctly, the subbing can be the backing. It is a matter of thickness.

    You might want to try an Oxonol dye. They wash out of gelatin more easily than Erythrosine. If I can get a chance I will look one up for you. I believe though that they are available from Honeywell in Germany.

    PE
     
  11. hrst

    hrst Member

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    Thank you! If you can find information about the specific dyes, I'd appreciate it.

    I can order from VWR.

    However, for these first stages, I try to avoid the extra complexity two-sided subbing would involve, and direct that effort into emulsion making itself. But it would be interesting to try anti-halo anti-curl backing at a later stage.
     
  12. Photo Engineer

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    It is Honeywell Antihalation dye, Oxonol Red 536 PINA.

    Have fun!

    PE
     
  13. dwross

    dwross Subscriber

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    I was tempted to opine that all the old recipes couldn't wrong, but I decided it was worth the effort to do a test just to make sure. I made a erythrosin-dyed gelatin filter and contact printed it over half an artisan film negative on Ilford Multigrade. For reference, I matched the amount of pink to your attachment. The only blocking is about what you'd expect from that amount of density. I think it's safe to assume erythrosin would work fine as a backing addendum. That said, I'm with you. Emulsion making is the fun part! And, actually, I love halation. I'm trying to enhance it in the series of images I'm currently working on.

    d
     

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  14. wildbillbugman

    wildbillbugman Member

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    Coating a gelatin backing on the film will help reduce curl.

    PE[/QUOTE]
    The best way to prevent curl :- Use glass as your backing ! Not that silly acetate stuff !:D
     
  15. Photo Engineer

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    Bill, I agree! Use glass.

    But, as for Erythrosine, it certainly does bond to gelatin and paper as well. It is sometimes difficult to remove from coatings and can leave a pronounced pink stain behind.

    PE
     
  16. wildbillbugman

    wildbillbugman Member

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    Seriously though, Is it erythrosine that leaves those pink stains on TMAX-100 after the fix?
    Bill
     
  17. John Shriver

    John Shriver Member

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    Isn't erythrosine the spectral sensitizer in the old orthochrome Verichrome film? That sample is sure the same color as unprocessed Verichrome.

    I've processed ancient Verichrome, and while the results were dismal (it doesn't have the stability of Verichrome Pan), the processed negative had no hint of magenta.
     
  18. Photo Engineer

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    Erythrosine is not used in any modern film. Its last use in commercial products AFAIK was in the 40s. Also, AFAIK, it was not used in any Verichrome film.

    PE