Of strange (jlajses .

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Chap. XXIII. r * ^

How Metal Looking-Glaftes are made. ~

B Ut Metal-GUsses are made another way. Wherefore if a Parabolical-Glass beto be made, draw a Parabolical line upon a brass or wooden Table; what iswithout it, must be filed away, that it may be equal, smooths and polished : fasten itupon an Axis in the middle, a'pd fit it with Instruments, that maybe fitly turnedabout, let there be clay with straw under it, made up with dung, that the Table be-ing turned about, it may receive a Concave form exactly i then let it dry, strewashes upon it, and plaister clay above that,'of a'COnvenient thickness ; let it dry bythe fire, ot if you will, by heat of the Sun, take it off, for it will easily part from theashes: unite,them together, that as much space may be between both forms,as youthink fit, for the thickness of the Glass : whfcn it is dry , cover it with this, leavingan open orifice on the top, and some breathing places, that the Air may breatheforth at it. Then make such a mixture; let them be put into a new pot that will en-dure the fire, and lute it well within, that it may hold the faster ; let it dry well,and do this twice or thrice over: set it to the fire, and melt in it two pounds of Tar-tar, and as many of white Arsenick ; when you see them fume, pour in fifty poundsof old brass, often used, and let it melt six or seven times, that it may be pure andcleansed; then adde twenty five ponnds of English Pewter, and let them melt toge-ther : draw forth some little of the mixture with some Iron, and try it, whether it bebrittle or hard; ifi it be brittle,put ip more Brass; if too hard, put in Pewter: or elselet it boil,that some part of the Pewter may evaporate: when it is come to the tem-per it should be, cast upon it two ounces of Borax, and let it alone till it dissolveinto smoke; then cast it into your Mold,and let it cool: When it is cool, rub it witha Pumice-stone, then with powder of Etnril. When you fee that the superficies isperfectly polished and equal, rub it over with Tripolis. Lastly, make it bright andshining with burnt Tin; most adde a third part of Pewter to the Brass, that themass may be the harder, and become more perspicuous.

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