Another thing to try is getting the glass very hot and dropping it into a bucket of ice water. The sudden temperature change may cause the bond to break.
SY said:Water won't do it. If the adhesive is a cyanoacrylate, a long acetone soak may work (but well away from any ignition source!). If it's PMMA, you'll have to get more aggressive, and a session with methylene chloride might be necessary. The latter should ONLY be undertaken by someone who knows how to handle explosive carcinogens.