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. CCLV. How to make Metal Mirrours, Concave Sphericks, or Parabolicks, usually called, Steel Burning Mir∣rours.

THE Authors cited in the former Chapter are very useful to be consulted on this occasion to demonstrate the Method, Use, and Excellency of these Mirrours; for which reason we shall say but little on that Subject.

The Moulds for them are prepared as in the for∣mer Chapter, whether Concave, or Convex, and for such as are flat, they may be cast on Sand.

The Metal of these Mirrours is called Steel, be∣cause it is of a very hard and bright Composure and Temper, and the harder the Metal, the better the Mirrour, and the easier to polish; the Whiteness of it is very convenient for giving the Quality of Burn∣ing, and not only for that, but several other Uses; if it be too Red, or Black, it alters the true Distance and Colour of its opposite Objects; you must there∣fore make them of this following Composition.

Take three Pounds of Copper, one Pound of fine Tin, half an Ounce of White Arsenick, an Ounce of Tartar: First, melt the Copper, then put the Tin in immerged in the Copper, else it will fume away in the Melting, and leave the Copper behind; these two being well melted together, cast in the Arsenick, and Tartar: After this let all melt for two or three Hours, and so Mould it.

Some Persons dose with the former weight of Copper and Tin, half a Pound of White Arsenick; ••thers instead of Arsenick,put in a quarter of a Pound

of Antimony. Here is another way to compound this Stuff of the following Ingredients; and after that another Composition much more excellent than ei∣ther.

Take a Pound of well refined Copper, melt it, then add three Pounds of fine Tin; as soon as these are well melted, add six Ounces of Red Tartar cal∣cined, one Ounce of Salt-petre, two Drams of Allom, and two Ounces of Arsenick, let these melt for three or four Hours, that the Salts may evaporate, and the Stuff will be fit for moulding; this Stuff is more solid and hard than the former, and much better to make the flat Mirrours for Looking. You shall be shewn how to polish them in the next Chapter.

We having promised to assign a much more ex∣cellent Stuff for Concaves than the former ones, will give it here; because of the hardness and compactness thereof, it is more capable of polishing, and conse∣quently much better than the rest.

Take Plates of Copper one Pound, mince 'em that they may be put into a Crucible, imbibing them with Oyl of Tartar; then powder a quarter of •• Pound of White Arsenick, and put these S. S. S. as we have shewn the Method elsewhere, until you fill the Cruci∣ble; pour on them afterwards Linseed-Oyl to co∣ver the Arsenick and the Copper; head and lute you•• Crucible, and when the lute is dry set it on a Sand-Furnace, letting the Sand arise no higher than the Head; heat the Furnace very gently till it arrive a•• a just degree, and the Oyl begins to evaporate; 〈◊〉〈◊〉 this time the Oyl will prepare the Copper for re∣taining the Arsenick, which must enter the Copper as easily as Oyl does Leather; set it again on fresh Sand, and increase the heat of the Furnace, giving i•• the same degree as before, until the Oyl evaporate•• and boyl up; then take off the Crucible, let it cool and break it, you'll find your Copper of several Co∣lours,

and would be much better, if instead of Arse∣nick, you made use of Orpiment.

Take of this Copper one part, of Latten two parts, melt the Latten on a smart Fire, and so put in the Cop∣per; when they are well melted, cast the Metal Drop by Drop into a glazed Earthen Vessel full of Water, over which lay a Bush, or Broom for the Stuff to go through; thus you'll have a Metal not to be touched with a File, nor Brittle, as good as any Steel for all uses whatsoever.

Take of this hard Metal three parts, and best Tin of Cornwall, which has no Lead in't, one part; melt the Metal before you put in the Tin; after these are well incorporated, you may fill your Moulds, &c.

This is the best of all our Compositions for ma∣king of all sorts of these Metal Mirrours; 'tis white, hard, not Brittle, and very easily polished exceeding fine.