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. CXXXVIII. The Way of Extracting a Tincture of Iargons d'Au∣vergne, and to make very fair and hard Diamonds thereof.

THOSE Stones may be made white and hard like the true Diamonds, by taking away their Tin∣cture, which is no contemptible Secret. There have been made Rose-Diamonds of them so fine and curi∣ous, that the best Goldsmiths have been mistaken in them, and thought them true Diamonds.

You must boil your Jargons in a Balneum of Mut∣ton-Suet, wherein they will lose all their Red Co∣lour and become White.

Then take equal parts of Emery of Spain, Rock-Crystal, Pumice-Stone, and Sulphurous Trepoly, the whole reduced into fine Powder, and searced through a fine Sieve, make a Paste of it with Aqua Vitae, wherewith cement your Jargons in a great Cru∣cible S. S. S. then cover it with another, and lute them well, then set it in a Furnace over a gentle Fire for half an Hour, then augment your Fire till it be hot enough for Fusion, wherein leave the whole for four∣teen Hours, then let the Fire go out, and the Cruci∣ble

cool of its self; wherein, after you have broke it, you'll find your Stones of a very fine Diamond Colour, hard, shining, and sparkling like the true ones, which you may polish and work up as the Gold∣smiths.

This Sulphurous Trepoly, which enters into the Composition of this Paste, being not commonly known, we will shew the way of making it, that we may leave nothing imperfect, which might be any Obstruction to the Proceedings of the Curious. Take equal parts of Trepoly, of crude Antimony and common Sulphur, and grind them to a fine Powder on a Porphyry Stone, and make them into a Paste with Vinegar, which being dry will easily crumble. This is the Sulphurous Trepoly which we make use of.

Some Persons in making the same Process of taking away the colour from Jargons, and giving them the hardness and whiteness of Diamonds, have made use of Barly-meol, wherewith they make a Paste with distill'd Vinegar impregnated with Lead, wherewith they stratifie their Stones, or Jargons, in a Crucible, covered with another, and well luted, which they afterwards put in a gradual, round, or Wheel Fire, for six Hours. But this way they could not give them the true Diamond-colour. Wherefore I ad∣vise those who would try this Experiment, to fol∣low our first Process, which has several times suc∣ceeded.

There are moreover some who stratifie their Stones with pounded Coal, which they put in a Cru∣cible covered and luted, which they set on the Fire six Hours, so that the Crucible be always red hot. I don't approve of this way, because the Coals may dry the Humour of the Stone, and calcine it.