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])

THE ARTIST's ASSISTANT. 7g

Class VII.* Of WHITE COLOURS.

White Flake is brought here from Italv ; it is
uied for oil or varnifh painting, where a very clean
white is required; and is a kind of cerufs or lead
corroded by acid.

There is a great deal fold at the colour (hops ready-
prepared ; that is, the true kind levigated, mixed
with ftarch or fome fuch fubftance. But it is be ft to
procure the white flake in a lump, and then levigate
it, and if it is thought proper, add any quantity of
ftarch in the grinding, that may render it fuitable to
work with.

W H I T E LEAD,

Is a corrofion bv acid from plates of lead, pre-
pared bv thofe who are concerned in it at a low
price. It is much employed m common purpofes of
painting, and may be ufed in nicer ; but will require
wafhing over, and then it is inferior to flake white.
Notwithstanding its cheapnefs, it is frequently adul-
terated by the makers or wholefale dealers, by add-
ing chalk or powdered talc, which may be feen by
comparing a pure piece with a fulpefted one : as
the fraud will appear by the difference of the weight.
But to prove it more exactly ufe the following
means :

<; Take an ounce of the white lead fufpefted ;
t: and mix it well with about half an ounce of
': nearl afhes, or of any fixed alkaline fait, and

" about

* Class VII. WHITE.
"White flake. Pearl white.

White lead. Troy white.

Calcined hartlhorn, . Egg-fhell white.