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. CIX. Observations for Pasts and their Colours.

WE might have inserted this Discourse in Chap. 91, as being the first of this Book; but we thought it better to place it here, where we will shew divers ways of making Pasts, no less fair than curi∣ous, and where it will be necessary to give some lit∣tle Instruction to those who undertake to make them, as also concerning the degrees of the Colours that may be therein imitated.

The making of these Pasts is the essential point of the Business; because on it depends the beauty of our artificial Gems: But the baking also is not of less Consequence, forasmuch as without that you cannot Succeed. It is not Enough to well Regulate the Fire during the time we have Noted in Chap. 92. whilst the matter is to stand in the Furnace, but you must also take care that the Crucibles don't break before the matter is well baked and purified: For if the Crucible breaks and you are forced to pour out the matter into another Crucible, the whole Work will be spoiled and the matter full of Pustles and Blisters. You had much better let the Crucible Cool, if it be not quite broken; then Lute it well, and put it in the Furnace again to make an end of baking. You must also take Notice not to break the Cruci∣ble to take out the matter before it be perfectly baked.

The curious may avoid these inconveniences, if in room of ordinary Crucibles they make them of the same Earth that the Pots for making Glass are made of, which will resist the Fire longer than we have occasion here for baking, and bear a more vi∣olent Fire than we have occasion for.

Those of Germany also will do very well for this business because they endure the Fire better than the ordinary ones. But I will yet abridge all these precau∣tions, by shewing an easy way to prepare the com∣mon Crucibles, which I have seen tryed, and resist the Fire a long time. Take an ordinary Crucible or rather one of Germany: Heat it a little in the Fire, then dip it into Olive Oyl, and let it soak a little of it in. Then take Glass reduced to an impalpable Powder, and strow it all over the Crucible, both without and within, as thick as you can, then put it into a Furnace in a small heat, and then increase the Fire to a melting Heat; then the Glass will Melt and Vitrifie so well with the Crucible, that it will en∣dure the Fire far longer than is required for our Bu∣siness.

We will also further remark that the Colours we here shew for Pasts are proportional to the Doses we give them; but those who would have them deeper or lighter, must regulate themselves accordingly: If they make small Stones for Rings, the Colour must be deeper by reason of their smallness: If they make greater, the Colour must be lighter, but deeper for Pendants than any other. The whole depends much on the Fancy of the Workman, who is to propor∣tion the Doses of the Colouring to the Work he de∣signs.

In speaking of these Colours in this Chapter, our design is only to shew more easie ways to those who exercise themselves herein, for otherwise we have sufficiently discours'd of them in the precedent

Chapter, as we shall continue to do in the follow∣ing.

We shall say nothing further here of calcined Copper, or Verdigrease, or Zaffer, or Manganese, having sufficiently done it before; but only adver∣tise the Curious, that there may be extracted from Gold a very fine Red, and one a little more obscure from Iron; an excellent Green from Copper; a Golden Colour from Lead; Blue from Silver, but a much fairer from Granats of Bohemia; which are low priz'd by reason of their smallness, but give a very fine Colour.

The same may be done with Rubies, Sapphire, and other precious Stones, as Chymists well know. If I should treat of all those Colours in this Tract, it would make it half as big again as I design it, and would be too prolix for our present Purpose; what we have shewn already, is sufficient to make very fine Works.