 The Baccarat glassworks in France created an opaque green uranium glass which they named chrysoprase from its similarity to that green form of chalcedony.At the end of the 19th century, glassmakers discovered that uranium glass with certain mineral additions could be tempered at high temperatures, inducing varying degrees of micro-crystallization.This produced a range of increasingly opaque glasses from the traditional transparent yellow or yellow-green to an opaque white.