DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.19571#0276
= 52 THE ARTIST'S ASSISTANT.
the manner of calcining lead, becaufe it is done in
works appropriated to that purpofe, and is fold by
the proprietors of thefe works, at a cheaper rate
than any particular perfons could pretend to manu-
facture it for their private ufe. The perfection
of red lead lies in its being thoroughly well cal-
cined, which is beft diftingnifhed by its rednefs, in-
clining to crimfon, and in its being pure, which
may be judged of by the brightnefs of its colour.
There is indeed no materials of a red colour cheap
enough to adulterate it with, except powdered
bricks, or fome of the red okers, and they would
immediately {hew themfelves in the vitrification of
the fmalleff. quantity, by the ftrong yellow tinge
they would give the glafs.
Pearl-afhes is the next leading article among the
fubftances ufed as fluxes in glafs, and they at prefent
moftly fupply the place of the Levant-afhes, the Ba-
rillas of Spain, and many other kinds, which were
formerlv brought here, as well for making glafs as
foap. In the kinds of glafs where perfect, tranf-
parency is wanted, as in looking-glafs plates, and
all kinds of window-glafs, falts are preferable as a
flux; for, as all the lixiviate, or fixed alkaline falts
of vegatables are the fame for this purpofe, when
pure, and thofe called pearl-afhes are purer than any
other which can be provided at a moderate expence,
the ufe of them is more expedient than of any other.
This kind of fixed alkaline falts, called pearl-afhes,
is prepared in Germany, Ruffia and Poland, by melt-
ing the falts out of the afhes of burnt wood ; and,
having reduced them again to dryneis, evaporating
away the rnoiflure, and calcining them for a con-
fiderable time, in a furnace moderately heated; but,
as
the manner of calcining lead, becaufe it is done in
works appropriated to that purpofe, and is fold by
the proprietors of thefe works, at a cheaper rate
than any particular perfons could pretend to manu-
facture it for their private ufe. The perfection
of red lead lies in its being thoroughly well cal-
cined, which is beft diftingnifhed by its rednefs, in-
clining to crimfon, and in its being pure, which
may be judged of by the brightnefs of its colour.
There is indeed no materials of a red colour cheap
enough to adulterate it with, except powdered
bricks, or fome of the red okers, and they would
immediately {hew themfelves in the vitrification of
the fmalleff. quantity, by the ftrong yellow tinge
they would give the glafs.
Pearl-afhes is the next leading article among the
fubftances ufed as fluxes in glafs, and they at prefent
moftly fupply the place of the Levant-afhes, the Ba-
rillas of Spain, and many other kinds, which were
formerlv brought here, as well for making glafs as
foap. In the kinds of glafs where perfect, tranf-
parency is wanted, as in looking-glafs plates, and
all kinds of window-glafs, falts are preferable as a
flux; for, as all the lixiviate, or fixed alkaline falts
of vegatables are the fame for this purpofe, when
pure, and thofe called pearl-afhes are purer than any
other which can be provided at a moderate expence,
the ufe of them is more expedient than of any other.
This kind of fixed alkaline falts, called pearl-afhes,
is prepared in Germany, Ruffia and Poland, by melt-
ing the falts out of the afhes of burnt wood ; and,
having reduced them again to dryneis, evaporating
away the rnoiflure, and calcining them for a con-
fiderable time, in a furnace moderately heated; but,
as