Exploding Glass Tears-- forgot the name, but it's called "(some Austrian city) tears." ?
You get a super-strong tear-shaped glass object that's incredibly strong-- stood up to repeated hammer blows on the bulb end. But when the "tail" is snapped, it bursts into powder. There's a wikipedia entry, but I need the name to find it again. I'd like to try it, but I need better info to avoid long trial/error sessions with hot glass.