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. XCIII. The Way of making a very sine and pure Salt of Tartar.

NERI makes use of no Salt of Tartar, in all his Preparations of Artificial Gems; notwith∣standing this Salt being prepared after a certain man∣ner, we shall here relate, for the sake of the Curious. It serves in a great measure to work the Crystal, being a true Vehicle, for the better introducing the Colours that are to be given, and which is of use for the Tin∣ctures several ways.

Those, who in their Operations of Artificial Gems, have made no use of Salt of Tartar, have with∣out doubt been ignorant of this fine Preparation of it; for if you use ordinary Salt of Tartar, there is a Sulphur and Foulness in it, which renders Crystal obscure, and consequently would be hurtful in these Operations.

To make this Salt, you must first calcine your Tartar, till it become Grey, and not to perfect White∣ness; and then dissolve it in warm Water to extract the Salt, filter that Water, and then evaporate it o∣ver the Fire; then you'll have remaining at the bot∣tom of the Vessel, a White Salt. To take away all Foulness from this Salt, dissolve it again in warm Water, then evaporate it again over a gentle Fire; take it off the Fire, and cast it into cold Water, and you'll find it will leave on the surface of the Water a thick Froth, which you must skim off with a Skim∣mer that has little Holes no bigger than a small Pins Head: Put the Vessel again on the Fire, and evapo∣rate the Water as before, then take it off the Fire, and cast upon it fresh cold Water, and skim it well as

before. Reiterate this Process till you find no more Froth; then Evaporate the whole over a gentle Fire till it be dry, and you will have a Salt of Tartar well purified, which is not so fusil as the other, be∣cause it is free from all that Unctuosity which causes the Fusion. Keep this Salt of Tartar in a Vessel well stopped, and use of it in Crystal with your Colours when you set them to melt.

Altho' this Salt of Tartar be very fine and pure, yet it is not that of the Philosophers, which has far more Virtue, and opens more powerfully the Metals and Minerals where it is employ'd, tho' it be of the same Nature as this, and extracted from the same Principle.

The Philosophers have moreover another Salt of Tartar extracted from Metalline Matters; and this last is far more Excellent than any others.

We will treat thereof at large in the Treatise we have promised, where we will explain the Virtues both of the one and the other, as well in Medicine as in the Business of Metals, and shew se∣veral very Curious Effects performed by their means.