I'm not sure that sticking would be caused by high surface tension in the
plexiglass - perhaps, but I would certainly believe that the cleanliness of the
surface would make a difference. I've experimented with this problem from the
opposite angle, namely trying to get the gelatin to "stick" to the plastic.
Recently I pretreated a plastic sheet with a thin (1%) solution of gelatin. A
subsequent coating of 7% gelatin adhered to this surface quite well. Basically
this is the the substrate pretreatment used in the preparation of collotype
plates given in the Keepers of Light book, pg 275.
My "wild guess" explanation for why this works, is that the dilute gelatin
solution is leaves some gelatin residue attached to the surface imperfections in
the plastic. The thicker gelatin mixture is then able to bind to these sites.
Some of my earlier tests showed that I could improve the bond by using a
slightly rougher surface, which supports this "guess", and also indicates that
you should stay away from abrasive cleaners if you don't want the gelatin to
stick. A wax pretreatment sounds like a good idea.
- Wayde Allen
(74160.3410@compuserve.com)