Earlier today I PM'ed PE with the following and while he was good enough to answer, he suggested I post to the forums and so I am. Seems this has become general interest rather than a specific error on my part.
I was hoping maybe you could point me in a direction for some trouble shooting with an emulsion I have made. I'd post this but it's a pretty specific question.
I have coated the emulsion onto the film base twice (Grafix Clear-Lay 3 mil -advertised to be cellulose acetate) and both times the emulsion has stripped off the base after drying. The first time it just curled up and fell off. This second time the emulsion remained adhered to the film so much so that as the emulsion shrank as it dryed it pulled the base into wrinkles and curled. However, when I went to cut it down to the needed size it came right off the base as I cut it. Two different subbing formulas were used between the first and second attempt. Same batch of emulsion.
1st: Wall's 1929 formula
2nd: as described in US Patent 2461475 (Kaszuba-GAF 1946) using ascorbic acid. Example IV in the patent.
The second coating was made with the emulsion at a temp of 45C. Sorry, but I don't recall the first coating temp. The film base was taped to glass which I warmed over the water bath. The glass was warm to touch but I cannot say the exact temperature.
The subbing seems to adequately adhered to the base. I can wash the base in water and it doesn't seem to come off and there is a clear difference in how the water runs off the subbed and non-subbed areas of the base. The issue seems to be between the subbing and the emulsion.
Here's what I can think of as initial problems to investigate:
1) the subbing is left to dry too long (overnight in the first attempt)
2) the subbing is not left to dry long enough (One sheet coated after an hour second sheet coated after 10 minutes)
3) Coating at too low a temperature so the gelatin in the subbing has hardened
4) Something wrong in the emulsion make.
I am using the grafix film on Denise Ross' suggestion. I also tried her trick of coating some with a thinned gesso to practice and had no problems whatsoever. The emulsion is mixed according to her TLF2 recipe with 10 drops 10% w/v solution sodium thiosulfate added as a sensitizer.
As a side note, with regard to the emulsion itself, even though it stripped, it is strong enough to hold together so I taped it to a piece of the base and exposed in camera. Developing in XTOL for 6 minutes by inspection gave a visible negative. Exposure was made at 1/8 sec, f4, under today's bright sunshine. I'm guessing an ISO of about 4 - so the sensitization didn't seem to work.
Any suggestions or references you would have would be welcome. Sorry for my long note. I'm off to mix up a 10% gelatin solution and see if I can't figure out what my problem might be.
**** And PE replied with....
I think that this question is worth posting but I will give and answer.
If emulsion strips off the support but remains as a cohesive film, then there is good hardening but poor adhesion to the support. With that understanding we can say it is one of two things, either the subbing is wrong, or the hardener is wrong. You don't mention the hardener, but generally aldehydes are used and in this case should probably work. Depends on the subbing. Wall has several formulas, one with Acetic Acid and Gelatin. In this case, the AA can inhibit (or accelerate) hardening depending on gelatin and pH.
I suggest costing between 100 - 110 F and using either glyoxal or chrome alum to harden coatings. If one will not work, the other usually does. Glyoxal takes about 4 hours to harden but CA takes up to 24 hours to harden. This includes interaction with the subbing layer.
Denise describes one of the acetates as having a subbing layer already. If so, double subbing can cause problems, but generally they are all minor and not like what you describe.
So, try changing hardeners first. If that does not work, get back to me.
***** And then I replied with the fact that I had forgotten the hardener and would have to try again..
And then later from PE....
If you have good apparent hardness with no hardener present, that is a clue. Something is helping give your emulsion a cohesiveness it does not deserve. Of course, this might just be cold gelatin on a repelling substrate. To test this theory, dip a small piece of the stripped emulsion into warm water (75 - 95 deg F) and see if it dissolves. If it does, then it was cold gelatin coming off a repelling substrate. If it remains cohesive, then it appears that something hardened your gelatin while repelling it from the subbing layer.
And now my reply to move this to the forum....
Thanks, PE. I'm going to move this to the forum and then reply when I figure something out. Right now I am just doing some trial and error with the 10% gelatin only mixture (no silver). Coating temperature of the substrate seems to have a lot to do with it because the warmer base coats better. Unfortunately, that isn't the whole problem because that will strip, too, if heated. Adding the hardener has also changed things because with hardener it seems to be harder to strip. (10% chrome alum added about .5 ml to 10 ml of 10% gelatin)
I'll also see about dipping some of the stripped emulsion into warm water.
We will figure this one out. Don't worry.
Oh, I'm thoroughly enjoying this! So no worries here!
OK, between plays, seeing that the hardener seems to help, I made a coating with the hardened gelatin but modified the subbing to raise the acetone to approximately 30%. The subbing formula given in US Patent 2461475 (Kaszuba et al, GAF, 1946) "Gelatin Subbing Compositions Containing Ascorbic Acid (Vitamin C)" in Column 4 line 25 is:
Vitamin C 0.2
Kaszuba says that examples IV and V can be substituted for any of the other formulas given. I found this formula interesting because I had ascorbic acid on hand and do not currently have glacial acetic acid. Also, I mispoke above about the base: the Graphix film is cellulose diacetate, not cellulose acetate.
Unfortunately this one also strips. I have a hunch that when the gelatin is drying (using moderate heat) the gelatin is shrinking and pulling the subbing away from the base because of the appearance of the diacetate where the subbing came off. To test this idea, I wet the stripped base and the area where the emulsion was applied is hydrophobic (the water runs right off - sort of like rain-x) and where the gelatin was not applied is still hydrophilic (as in it stays wet.)
Looks like the problem is caused by poor adhesion of the subbing to the base.
Also, a test of the earlier gelatin without hardener does dissolve in warm water. Since the actual emulsion has no hardener and strips in the same way I will presume that it, too, will dissolve.
Now that my glass is free, I will try to make a good quality coating with hardened gelatin. (My last with hardened gelatin was without the glass on a scrap of diacetate)
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I suspect (just a guess) that the subbing is not right for the support. If the subbing comes off as you indicate, then it isn't really adhering to the base which is the main purpose of a subbing layer.
Well, that's because the base (Graphix Clear-Lay) is PVC, not cellulose diacetate. Last night, I cut a piece into very small pieces and put in a jar with straight acetone to soak overnight. Nothing happened. Acetate should have dissolved. A web search this morning shows that the material is actually PVC and not their acetate product. Looks like I ordered the wrong item or maybe "Clear Lay" used to be diacetate and changed to PVC. Thankfully, with plenty of school projects still to come I doubt it will go to waste. Maybe I can find a solvent for PVC? idk.
I will get some actual acetate, try this again and report back.
Last edited by kb3lms; 02-06-2012 at 08:37 AM. Click to view previous post history.
I am watching this thread with great interest, as I have had my own struggles with coating 'film'.
IIRC, strong solutions of acetone (and most ketones) usually soften PVC. Perhaps there is some plasticizer or other additive in the product. I don't know if it's the case with Clear-Lay, but I've found that many plastics and papers benefit from a wash with water + surfactant to remove manufacturing residues (lubricants, powders etc., used to facilitate machine production, packaging), sometime a good puff of compressed air is enough.
I'm currently using fixed-out imagesetter film as a base material: it is very clear, dimensionally stable, and the subbing/emulsion layer is very tough.
Looking forward to hearing more about your adventures!
Last edited by Hexavalent; 02-06-2012 at 11:40 AM. Click to view previous post history.
Reason: additional information
I have a few feet of 4" wide (or thereabouts) acetate here somewhere. I usually use the Melinex from the Formulary, but I could check out the acetate or send a strip to you guys.
I have some of the Grafix acetate product on order. They sell it in a pad of 9x12 sheets for about $9.00. From what I can tell, that ought to work. I also have a lead on some other pre-subbed material and looking forward to trying that, too.
For posterity, here is a scan of the negative I mentioned above:
Size is 35mm. This is only the emulsion smoothed out onto a microscope slide as best possible.
Last edited by kb3lms; 02-06-2012 at 09:29 PM. Click to view previous post history.
Reason: Trying to add the image