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THese colours are not to be made without a great deal of Precaution, which this needs as much as any. To succeed well, you must have in the Furnace a Pot filled with 40 pound of good Cry∣stall••Fritt, carefully skimm'd, boil'd, and purifi'd, without any Manganese: having arrived thus far, you must take 12 Ounces of the Powder of Small leaves of Copper thrice calcin'd, as we have shewn
chap. XXX. And half an ounce of Zaffer in Pow∣der, prepared as in chap. XVII. Mix these Pow∣ders together, then put them at four times into the Pot, that they may the better mix with the Glass, stirring them at each time well, as you put them in, for fear it should swell too much, and run over. Two hours after the whole is incorporated, well mixed, and pretty well settled, try if your colour is deep enough then let it rest, tho' the Sea-green or sky colour seems at first Greenish you need not be con∣cerned at that: For the Salt in the Glass will consume all that Greenness, and change it into Blue.
After your Metal has stood at rest 24 hours, it may be wrought, and you'll have the colour deeper or lighter, according to the quantity of Powder you have used in it. There is no other Rule in that, but the Phancy of the Workman, which is the reason it cannot be ascertained; besides the Matter we use to tinge Glass, makes it have some more colour, some less, which proceeds from the Preparation of it.