A lot of crystal will be lead crystal (at least in part). Please don't! Especially if it's old crystal.

The oscillator circuit, which is usually quartz crystal controlled with the quartz crystal in a temperature regulated oven to stabilize its resonant frequency.

On Crystal Island.

(appears when you've fixed the oven workbench in the Temple)

Weight your sample

Heat in an oven then weight them out again, when this weigh is constant then its done.

Coz in this expermnt oven containing four probes is used to maintain the continuity with crystal