Enamels and enamelling; an introduction to the preparation and ...

XIV.
SMELTING THE CHAEGE.
In this operation all the precautions imaginable must be
taken to prevent loss through the breakage of the crucibles,
especially the first time they are used. The following is the
method pursued :
The crucibles, after being carefully examined, are bored
with a conical steel bit, of sufficient breadth across the bottom
to make an aperture large enough to allow the fused mass to
run out. As the ground enamels are never so fluid as those
intended for the covering layer, the holes in crucibles for
fusing the former must be larger than the others, i.e., about
J inch in diameter, as compared with T^ to ^ inch.
The object of making the holes taper is to facilitate the
removal of the plugs, with which they are closed while the
mass is being fused. These plugs are preferably made of
quartz meal, moistened with gum water so as to form a plastic,
coherent mass which, under the heat of the furnace, sinters
together and prevents the contents of the crucible from escaping
until the plug has been displaced by the insertion of a pointed
iron rod. When the crucible is to be charged anew a fresh
plug must be made and put in, and with this object the neces-
sary quantity of plastic material is fixed on the tip of an iron
rod, by means of which it can be pressed into the plug hole, an
iron disc faced with clay being provided on the rod to protect
the operator's hand from the heat of the furnace.
Unfortunately it often happens, particularly when the