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])

256 THE ARTIST'S ASSISTANT.

or parchment fize is ufed. Some recommend tobacco-
pipe clay in the place of whiting, and add a little
lamp black, to give a iiiver-like greyifhnefs to the
compolition.

Of the NATURE and COMPOSITION
of GLASS.

HPHE materials employed to give a bodv to glafs
are, fand, flints, talc, fpar, and fome other ftony
and terrene fofhTes.

Sand is, at prefent, a'mofl the only kind oF fub-
ftance which is ufed in this intention in the Bri-
t'iffi manufactories or glafs, and with great reafon,
as it extremely well anlwers the purpofe ; and does
not demand the previous preparation of calcination
that is neceffary with re!pe£t to Hints and other
ftones : and as it can be with certainty procured, in
any quantity demanded. The kind of fand mofl fit
for making the white tranfparent kinds of glafs, is
that brought from Lvnn in Norfolk, by the name of
which place it is diftinguifhed : and there is alio
another kind of this, but inferior, brought from
Maidftone, in Kent ; it is white and fhinincr, and,
examined by means of a microfcope, aopears to be
fmall fragments of rock chrvftal, from which it does
not feem, by any experiments, to differ in its qua-
lities ; and the glafs formed of it may, therefore,
properly be conhdered as made of chryftal. The
introduction of it into the manufactories of glafs in
this country has almcit wholly fuperfeded that of
flints, from which it no way differs in this appli-

* J 11

cation,

i