The Artist's Assistant, In the Study and Practice of Mechanical Sciences: Calculated for the Improvement of Genius. Illustrated with Copper-Plates — Birmingham, [ca. 1785]

Seite: 202
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https://digi.ub.uni-heidelberg.de/diglit/assistent1785/0216
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202 THE ARIIo i s ASSISTANT.

When the plate tarnifhes in the part where you are
at work, a little vinegar and fait, kept by you in a
vial, will take it off, wiping it dry with a clean rag.

Avoid, as much as poffible, over-fcraping any
part before the firft proving, as by this caution the
work will appear the more elegant.

Of CASTING.

To prepare clay in fuch a manner as to he fit to male all man*
ncr of moulds to cajt gold, filver, and other metals in.

rJ"'AKE as much clay as you will, put it into an
earthen pot that is glazed, and cover and lute
it very clofe ; then put it into a potter's furnace, and
let is fland as long as other earthenware. After it is
burned and cold, grind the clay upon a colour ftone
very fine, fift it through a fine hair neve into clear
water, and, after it is fettled, pour off the water and
grind the clay once more upon the ftone, as fine as
poffible ; then wafh it again in fair water as before,
and fet it in the fun, or in a warm place, to dry.

After this burned and wafhed clay is thoroughly
dry, take thereof three pounds, fal-armoniac two
pounds, tartar two pounds, and vitriol one pound ;
mix them together, and put this mixture into one
or two pots ; pour upon it about feven quarts of
clean water, and boil this compofition for fome
time ; then take this water, whilft it is warm, and
mix your burned clay therewith to fuch a confiftence
that you may form it into balls; lay thefe in a warm
place to dry, and, when dry, put them into an earthen-
pot
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