My concern with Bouin's in the microwave are two-fold.  I think the buildup of formalin vapors in the microwave is more a safety concern than the picric acid.  If you do this, make sure your microwave is properly vented.  The other issue concerns boil over.  The stuff just doesn't wash off the inside of the microwave.  Placing the plastic coplin jar in a plastic ziplock bag before microwaving should address both these concerns. After microwaving, move the jar and bag to a fume hood for handling.

Teri Johnson
Managing Director Histology Core Facility
Stowers Institute for Medical Research
1000 E. 50th St.
Kansas City, Missouri  64110
tjj@stowers-institute.org