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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1 cm

i: Evaccrate the whole to about an ciVhth : and
<; then remove it into a china cup or bafon of pro-
per fize, and evaporate it to drynefs; collecting
" it into a mats as it becomes of a ft iff confiftence."

TERRA di SIENNA unbumt.

Mention has been made of this pigment being a
native ochrous earth, brought from Italy ; that cal-
cination changes it from yellow to red—therefore
thofe that choofe to ufe it as a yellow, fhould take
care to have it extremely well levigated, and it will
ferve as a deeper fhade by many degrees than any
of the other okers, and of a luperior brightnefs.


This for ufe is much fuch another colour in yel-
low as vermillion in red, and will ftand equally
well with that. It is a preparation of mercurv,
hy calcining it together with oil of vitriol, and is
much brighter than any other yellow uled in oil,
except king's yellow. The preparation:

"Take of pure quickhlver, and oil of vitriol,
<; each fix pounds. Put them into a retort ; to
which, being placed in a fand bath, fit on a re-
t; cciver : and diftil them with a ftrong fire, while
any fumes appear to rife into the receiver : urging
4- it at la ft with as great a heat as the furnace will
<; bear. When the retort is again cold, remove it
" out of the fand bath : and having broken it. take
'•" the white mafs, which will be found at the bot-
" torn of it, and break it to a orols powder ; and
il having put it in a glafs mortar, pour water on it :
" which will immediatelv convert it to a yellow

<; colour.
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