I came across this uranium glass item; seller from whom I was buying a vase had it on ebay for 99p, so couldn't resist. Is this a piano insulator? I haven't bought any before and don't know if they came in an oval shape. Is insulator or caster a better term? Is it a salt? although it seems heavy and clunky for a dining table. It's very heavy, almost 400g. 11 cm long, 8 cm wide, 4 cm tall.