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. LXXVIII. The Way to tinge Natural Crystal of a Viper colour.

THE Green Viper Colour is not disagreeable, but it is very dangerous to make, by reason of the Materials whereof it is composed, if you are not very careful in making it. Take two Ounces of Rock Crystal of a good Water, two Ounces of crude Antimony, and as much Orpiment, with one Ounce of Sal-Armoniack; reduce these three last into Pow∣der: Stratifie with these Powders the Pieces of Crystal, in a good Crucible; cover it with another that is bored through the bottom, lute them well to∣gether, and when the Lute is dry, put them in the middle of the Coals in a Furnace, let them be gently lighted that the Crucible may grow hot by degrees. It will smoak very much when it first grows hot, wherefore this Operation must be made in a large Chimney, that the Smoak may fly away, and you must go out of the Laboratory, because it is very dangerous and may prove Mortal. Let the Fire kin∣dle of it self, and the Crucible grow cold; then take out the Pieces of Crystal which lie on the top of the Crucible, which will have the Colour of Rubies, and be marked with fine Spots; and those which are at the bottom will for the most part have the Colour of Vipers. Separate the other pieces from them, which will be of other Colours, and polish the whole at the Wheel like other Stones, then with Foils you may set them in Gold. These Stones will be of a very agreeable colour. You might tinge a great number together, but that would be more charge∣able.