Unannealed

A Prince-Rupert's-drop, which is a tear of unannealed glass, lasts indefinitely, if you keep it from meddling hands; but break its tail off, and it explodes and resolves itself into powder.

The experiment may be varied in this way: Placing in front of the polarizer a plate of unannealed glass, you have a series of beautifully coloured rings, intersected by a black cross.