Quite a good coating on acetate
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! )
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.
Last edited by hrst; 04-22-2010 at 05:33 AM. Click to view previous post history.
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?
For up from the ashes, up from the ashes, grow the roses of success!
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.
Very nice work.
Sorbitol will help prevent cracking.
Coating a gelatin backing on the film will help reduce curl.
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?
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There are special dyes for that. I can look them up. But, basically, yes.
Originally Posted by hrst
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.
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.
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.
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.