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. CXLII. Another Way to harden Crystals and Diamonds of Alanson.

CRYSTALS also acquire hardness in the Paste we are now going to describe, because their Hu∣midity exhales, and they become more fixt.

Take Barly-Meal well sifted, with Petroleum, or Rock-Oyl; then cut that Paste in the middle, and put all your Stones in order, so that they may not touch one another. Then cover your Stones with the other half of the Paste, then put it in a Crucible covered with another, and luted well together, and let it dry. Then set this Crucible in a gradual Wheel-Fire from five to six Hours, a small Fire the two first Hours, which en••rease from two to two Hours, till the end of the six; then let the whole cool of it self. Then break your Crucibles, and you'll find your Stones very fine, shining, and sparkling like fine Di∣amonds, which repolish at the Wheel, and set by a skilful Workman.