The artists repository and drawing magazine: exhibiting the principles of the polite arts in their various branches (2.1788)

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fine) to form a coat, or fuperficies, thereby remlipg the
menftruum on all fides. Sal ammoniac, pulverized with
the rofin, was found to preferve interftices, but this
applies only dccafionally. There are feveral gums
which poflefs nearly fimilar properties ; but the follow-'
ing appears fuperior, and is (excepting the change of
gum juniper for gum copal) the method of Monf.
Le Prince.

Grind a fufHcient quantity of gum copal; divide it by
fating, into three or four parcels at pleafure, according to
their refpective finenefs : the fineft powder Serving for
the lighter parts of the fubject to be treated, fuchas dis-
tances, fey, Sic. The fecond for middle tints ; the
coarfer for fore-grounds, and other very dark places.
To perform this, the fieves rauft vary in their finenefs.
Sift on the plate a fufHcient quantity of the finer pow-
der ; the plate will now appear of an uniform white,
unlefs clofely examined, when the interftices will be
very difcernable heat the plate gently, till the gum
changes from its white colour, and is fo far melted as
to fix on the plate, from which it is fcarce to be diftin-
guifhed by its colour. When cold, it is ready for re-
ceiving the aqua-fortis. Stop out the lights, &c. as in
common biting.

When the biting is over, (which does not laft long
to the fine powder) clean the plate by heating it, and
apply a little oil, if neceffary. Thofe parts which are of
a juft colour muff then be fecured by flopping them
out, and the fecond powder be treated as the firft, and
the coarfer powders, or rather grains of gum, as the
fecond.

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