The art of glass shewing how to make all sorts of glass, crystal and enamel : likewise the making of pearls, precious stones, china and looking-glasses : to which is added, the method of painting on glass and enameling : also how to extract the colours from minerals, metals, herbs and flowers ... : illustrated with proper sculptures / written originally in French, by Mr. H. Blancourt, and now first translated into English ; with an appendix, containing exact instructions for making glass-eyes of all colours.

CHAP. CXLIV. The Way to turn White Sapphire into true Diamond.

THE White Sapphire being fine and fixed, is on∣ly imperfect, by reason of its wanting colour and hardness, which may be remedied by means of Art, and be made to surpass Nature, because she on∣••y would have made it a perfect Sapphire, but Art can ••urn it into a true Diamond.

Only Fire can cause this Effect, in changing its Natural colour, and giving it that of a Diamond. Thus take very fine Sand, wash it in several Waters ••o clean it, till the Water become clear, and then dry it. Of this Sand fill a Crucible half full, then ••ut in your Sapphire, and fill it up with the same Sand. Then cover your Crucible with a cover of the same Earth, or with another Crucible; lute the whole

with a good lute, as we have heretofore shewn, lay it on an Inch thick, and let it dry in the shade. Be∣ing dry, set it in a Glass-house Furnace, approach∣ing it nearer the Fire by degrees, and leaving it twelve Hours in the same degree of heat. Then withdraw it little by little for the space of six Hours, and let it cool gently. The Crucible being cold, break it, and you'll find your Sapphire within, which will have all the Qualities of a fine Diamond; that is, its shining and hardness. Repolish it at the Wheel, and work it.