DOI Page / Citation link:
https://doi.org/10.11588/diglit.19571#0273
THE ARTIST's ASSISTANT. 259
water, and continuing them there till they become
intirely white, even to the moft interior part ; which
will require a greater or lefs time, according to their
magnitude, and the degree of the heat of the furnace :
when they are thus rendered white, they muft be
taken out of the fire, and inftantly immerfed in cold
water, where they muft remain till they be again,
cold ; and then they will be found, if duly calcined,
to be cracked and fhivered into flaky pieces, and to
become fo fwiftly brittle as to be eafily reducible to
powder; fome part will, neverthelels, be always
found infufliciently calcined, which may be diftin-
guifhed by their harder and more obdurate confid-
ence ; and they muft be carefully feparated, in order-
to be recalcined, as they will otherwife greatly re-
tard and impede the powdering of the duly calcined
parts ; thofe which are properly calcined, muft then,
be levigated, by means of mills, or other implements,
accordingly as the quantity or opportunity may make
it expedient; and they will then be fit for ufing in
the compofitions for glafs.
Talc of various fpecies has been likewife ufed in
the fame intention as fand and flints, but feldom in
large works ; it fometimes requires a calcination, in.
order to its due preparation for entering into the
compofition of glafs ; but neither fo great a heat, nor
the quenching in cold water, are neceffary for bring-
ing it to a proper texture to bear powdering. Some
forts of talc are much more quickly verifiable than
others, and fuhng eafily with either fait of tartar, or
lead, may therefore be ufed in default of flint, or
f:md fufHciently white ; but with refpeQ: to larger
manufactures} the ufe of flints is more eligable, as
K k a they
water, and continuing them there till they become
intirely white, even to the moft interior part ; which
will require a greater or lefs time, according to their
magnitude, and the degree of the heat of the furnace :
when they are thus rendered white, they muft be
taken out of the fire, and inftantly immerfed in cold
water, where they muft remain till they be again,
cold ; and then they will be found, if duly calcined,
to be cracked and fhivered into flaky pieces, and to
become fo fwiftly brittle as to be eafily reducible to
powder; fome part will, neverthelels, be always
found infufliciently calcined, which may be diftin-
guifhed by their harder and more obdurate confid-
ence ; and they muft be carefully feparated, in order-
to be recalcined, as they will otherwife greatly re-
tard and impede the powdering of the duly calcined
parts ; thofe which are properly calcined, muft then,
be levigated, by means of mills, or other implements,
accordingly as the quantity or opportunity may make
it expedient; and they will then be fit for ufing in
the compofitions for glafs.
Talc of various fpecies has been likewife ufed in
the fame intention as fand and flints, but feldom in
large works ; it fometimes requires a calcination, in.
order to its due preparation for entering into the
compofition of glafs ; but neither fo great a heat, nor
the quenching in cold water, are neceffary for bring-
ing it to a proper texture to bear powdering. Some
forts of talc are much more quickly verifiable than
others, and fuhng eafily with either fait of tartar, or
lead, may therefore be ufed in default of flint, or
f:md fufHciently white ; but with refpeQ: to larger
manufactures} the ufe of flints is more eligable, as
K k a they