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..