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])

142 THE ARTIST'S ASSISTANT.

perfection of the flux to be foft, or run eafilv into
fufion. But the great point, with rcfpeft to this par-
ticular, is, that when feveral mixtures of colours and
fluxes are ufed at the fame time, they fhould all cor-
refpond to each other in the degree of this quality.
Chherwife fome would be rendered too fluid, and
perhaps run the matter of the enamel ground into
fufion, and mix with it, while others remained folid
and infufRciently fufcd themfelves. It is always
neceffars', Lkewife, that the enamel of the ground
fhould be confiderably harder than the mixtures for
the colours: for if they both melt with the fame de-
gree of heat, they will neceffarily run together.

It being requifite that the body painted in enamel
fhould undergo a heat fufficient to melt foft glafs, the
matter of fuch body can only be gold, filver, copper,
porcelean. or china-ware, hard glafs, and earthen-
ware. And where the metals are ufed, if the paint-
ing be of the nature of a picture, or demand a vari-
ety of colours, it is neceffary that a ground of white,
or fome other colour, fhould be laid on the metal ; the
body of which ground muft neceffarily be of the fame
vitreous nature as the flux, but harder. As nothing
elfe can endure fo great a heat that is capable of in-
corporating with, and binding the matter of the
white, or other colour, to the furface of the metal.
The ground, therefore, makes another principal fub-
ftance uled in enamel painting.

The third fubftance is the colour, which muft
likewife be a body capable of fuffering the heat of
melted glafs ; and fuch as will either itfelf be con-
verted into glafs, or kindlv incorporate with it, in a
melted {late. This, of courfe, confines the matter of
fuch colour to metals, earths, or other mineral bodies;

all