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]

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148 THE ARTIST'S ASSISTANT.

There is a fort of ftone, which the French call
mi-Ion, that forms the upper craft, and lies round
the free-ftone in molt quarries. This flone will lofe
its tenacity in a moderate fire, and, when calcined,
runs much fooner into vitrification than either flints
or fartd. It is therefore, when it can be obtained, a
better matter for the body of fluxes or foft enamel,
than either of the other. It will, with the fame
proportion of the fluxing ingredients, make a much
fofterflux; or, it otherwife admits of the diminu-
tion of the proportion of feme of them ; which,
for many experimental reafons, is in certain cafes an
advantage.

Of the fubjlances uffdfor producing a white colour in enamel^
for forming the grounds.

Putty, or calcined tin, is ufed as a body of colour
for the enamel grounds. As tin is very troublefome
in calcination, requiring a long continuance of fire,
and to be Ipread into a very thm furface, it is much
the belt way to procure it for the purpofesof enamel-
ling ready calcined, of thofe who make it their
proper bufmefs to calcine it, for the ufe of lapida-
ries, and other artifts who ufe it. For they have
large furnaces, fitly conflrufted for performing that
operation in large quantities, and can confequently
afford it much cheaper than it can be prepared in
fmall quantities; befides the fparing the trouble. It
muff be demanded of them by the name of putty ;
and care muft be taken that it be not fophifticated,
which it feldom fails to be before it comes out of
their hands for common purpofes. The fophiftica-
tion, which is generally by chalk, lime, or fome
fuch white earth, may be thus diftinguifhed. Put

the
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