According to Sheperd Paine's book on how to build dioramas, the best coat
is *no coat at all.* Spraying any kind of fixative over the pastels may
make them clump up, spoiling the effect. Paine suggests that you affiix
the model to a permanent base first, then use pastels as the final step.
After that, don't touch the model itself -- pick it up by the base.
Mark