When a ſmall quantity of any gypſum is melted together with borax, the glaſs becomes colourleſs and tranſparent; but I have found ſome ſorts of alabaſter and ſparry gypſa that, when melted in ſome quantity with borax, yield a fine yellow tranſparent colour, reſembling that of the beſt topaſes.