Judy (or better: Carmen...), the hardening usually is just for the transfer
paper's gelatin coating. And sometimes for the final images. NEVER for the
tissue. There is certainly no alum or whatsoever hardening substance mentioned
in any formula for pigment tissue in the world. I really start getting bad
conscience. My demo must have been so weird that I left your student in total
confusion ):-(
Fighting the bubbles: She should try to coat the pigmented gelatin on a clean
sheet of plexiglas. After gelling, a wet sheet of paper is laid on top of the
gelatin and carefully rolled or squegeed down. It is even possible to do this
combination work under water, as if one was to combine the exposed tissue with
the transfer paper for developming. After drying (over night) one can peel off
the paper from the plexi with a perfect gelatin surface. The bubbles (which have
been on the surface of the gelatin during coating) now are between the paper and
the gelatin.
Regards,
Klaus
Klaus Pollmeier