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])

274 THE ARTIST'S ASSISTANT.

To make an artificial chryfolite :—This flone is of
a green colour, and fome have the call of gold; to
imitate it, take natural cryftal prepared two ounces,
red lead eight ounces, crocus martis twelve grains;
mix the whole finely together, and proceed as before,
only leaving it a little longer in the furnace.

Another procefs for counterfeiting precious ftones;
take of black flint ftones what quantity you pleafe,
and put them into a pail of hot water, and being wet,
put them into a hot furnace ; thi- will prevent their
flying into fmall pieces ; or elie warm them thorough-
ly, by degrees, before you put them into the furnace ;
-when you fee that they are thorough red hot, then

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quench them in fair water, and they will look of a
fine white colour, dry and pulverize them very fine ;
this you may do in an iron mortar, but, as it may
contract fome of the iron, it will be proper, after
you have taken it out, to pour on it fome aquafortis,
which will clear it of the iron, and fo difengape it
from all filth and impurities ; wafh it in feveral clean
hot waters.

This powder, thus prepared, is fit to be ufed for
making the fined glafs, and for imitating the cleareffc
and moll tranfparent gems, efpecially thofe that re-
quire the luftre of a diamond or ruby : as for a fa-
phir, emerald, topaz, chryfolite. Ipirel, amethift, &c.
your labour with aquafortis may be faved, if your
mortar be bright and (tee from ruft ; fuch as have a
mortar of porphiiy, or fuch like ftone, have no oc-
cafion to ufe an iion one, but will fave themfelves
a preat deal of trouble.

In cafe you cannot have black flint ftones, you
may content yourfelf with pebble, but flint is far

preferable,