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)