crisping refers to the practice of banging an opiate that is orginally in pill form and is now in a liquid (but usually gel) form. (Banging refering to shooting the opiate into one of SWIY's veins usually).
Some opiate pills gel up when trying to add water to them for the purpose of banging them. By putting such a gel into a microwave (or other similar low heat sources) for a short period of time it is possible (but potentially unwise) to dry out the gel, and make it easier to shoot. However this does not make it any safer to shoot.
would highly recommend against doing this.