DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.19571#0278
264 THE ARTIST'S AS SI STAN T.
tinguifh this fraud, the following method is pro-
poled as eafy and certain :
Take a quantity of the fait fufpecled, and, after it
has lain in the air, fo as to be a little foftened, but
not melted, put it in a fire-fhovel, and hold it over
the fire where the heat is pretty ftrong. If it con-
tain any common fait, a crackling, and, as it were,
flight explofion will follow, as the fait grows hot ;
which decrepitation is a certain mark of common
fait wherever it is found.
The pearl-afhes require no preparation, except
"where extreme great tranfparency is required, as in
the cafe of looking-glafs, and thebeft window glafs ;
in which cafe a purification is neceffary, in the
manner which will be fhewn in fpeaking of thefe
particular kinds.
Nitre, which in its refined ftate, is commonly
called faltpetre, has been formerly much ufed as a
flux in the finer kinds of glafs, and is now like-
wile employed in mo ft compofitions of the fame na-
ture. But this is a noted one by thofe who are at all
acquainted with the principles of the art, not fo
much in the intention of a flux, as of that of a co-
lorific ingredient, from its power of rendering glafs
cclourlefs, by destroying the phlogifton in lead, or
in any kind of vegetable or animal matter, which
may tinge the glafs. As a flux, it is lefs power-
ful than fixed alkaline falts of vegetables, and, be-
ing dearer by much, its ufe would, therefore, be in
proportion lefs expedient than that of pearl-afhes,
if it were to be ernploved in this view only. The
faltpetre that is ufed here is brought from the Eaft-
Indies, in the form of what is called crude nitre,
and in commercial language rough-petre ; in which
ftate
tinguifh this fraud, the following method is pro-
poled as eafy and certain :
Take a quantity of the fait fufpecled, and, after it
has lain in the air, fo as to be a little foftened, but
not melted, put it in a fire-fhovel, and hold it over
the fire where the heat is pretty ftrong. If it con-
tain any common fait, a crackling, and, as it were,
flight explofion will follow, as the fait grows hot ;
which decrepitation is a certain mark of common
fait wherever it is found.
The pearl-afhes require no preparation, except
"where extreme great tranfparency is required, as in
the cafe of looking-glafs, and thebeft window glafs ;
in which cafe a purification is neceffary, in the
manner which will be fhewn in fpeaking of thefe
particular kinds.
Nitre, which in its refined ftate, is commonly
called faltpetre, has been formerly much ufed as a
flux in the finer kinds of glafs, and is now like-
wile employed in mo ft compofitions of the fame na-
ture. But this is a noted one by thofe who are at all
acquainted with the principles of the art, not fo
much in the intention of a flux, as of that of a co-
lorific ingredient, from its power of rendering glafs
cclourlefs, by destroying the phlogifton in lead, or
in any kind of vegetable or animal matter, which
may tinge the glafs. As a flux, it is lefs power-
ful than fixed alkaline falts of vegetables, and, be-
ing dearer by much, its ufe would, therefore, be in
proportion lefs expedient than that of pearl-afhes,
if it were to be ernploved in this view only. The
faltpetre that is ufed here is brought from the Eaft-
Indies, in the form of what is called crude nitre,
and in commercial language rough-petre ; in which
ftate