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WE have shewn the way to make Crocus Martis for Colouring Glass, and now we will shew that of Copper, which is very near in nature to the other as we have remarked; And which dis∣solves
in the same Acids and Corrosives. Venus as well as Mars (or Copper as well as Iron) gives us diffe∣rent Colours, which proceed from different ways of preparing them, as we shall see in the following Chapters.
Merret pretends that Brass gives us a finer blue than Copper, by reason of the Lapis Calaminaris which is mixt with it, and partly causes the Colour.
Of all Metals Copper is only used (as Allay) to give malleability to Gold and Silver in Coin: It melts easily in an indifferent heat, but it is calcin'd into powder with difficulty. There are several ways of Calcining Copper, here follow five of them by help of fire. The first is of Copper alone with∣out any addition; the second by the addition of Sulphur; the third by Vitriol; the fourth of Brass alone divers ways; the fifth by a preparation of the Vitriol of Venus. These preparations are the best, and of more value than those prepared by Spirits and Cor∣rosives. All these different ways of Calcinations and Preparations of Venus, shall be explained in several Chapters of this Treatise, whither the curious Rea∣der may have recourse.
The little Plates or Leaves, whereof we are now to shew the preparation, are a sort of Copper or Brass exceeding thin, approaching the Colour of Gold, called Festoons. These Plates are made of this Colour by Lapis Calaminaris, which does not only Colour the Copper, but augments its weight; this Brass being well calcined tinges Glass of a Blue, and Sea-Green. The way to calcine it is this.
To avoid the expence of buying new, you may make use of those leaves that have been already used and worked, they being good, and cut them with Scissers into little pieces, and put them into a
Crucible covered and luted, in the mouth of a Furnace to Calcine, and let them stand there for four days, at a Coal fire, so that the leaves may not melt: For then they would be unfit for this use. The four days being expired, the whole will be calcined, beat them on a Porphury Stone, and Searce them thro' a fine Sieve; and you will have a blackish powder, which you must spread on Tiles, and put it into the same Furnace for four days longer; then take it out and blow off the ashes that may be fallen on it; then reduce it again into Pow∣der, searceing it thro' a fine Sieve as before, and keep it for use.
You may know when it is well Calcined, if the Glass rises and swells when you put it upon it, if it does not you must calcine other leaves, those being not Serviceable by reason they are burnt in the Calcination.