International studio (14.1901)

Enamelling

RELIQUARY, ILLUSTRATING THE USE OF CHAMPLEVE ENAMEL

SOUTH KENSINGTON MUSEUM

bined with oxides of metals. The flux is com-
posed of silica — that is, of powdered flint or
silver sand; minium, which is red lead; nitrate,
or carbonate of soda, or potash, all melted
together in a crucible until there are no bubbles
left in it. This flux, which is the base of all
enamels, is combined with different metallic
oxides in various proportions. To a certain point,
beyond which no combination occurs, the more
oxide fused with the flux, the darker in tone and
richer in colour will the enamel become, and vice
versa. Transparent enamels are made opaque
either by the addition of calx, which is a mixture
of tin and lead calcined, or else by arsenious acid,
that is to say, of white arsenic. The flux when
combined with a precipitation of gold and tin,
called purple of Cassius, gives a beautiful purplish-
red ; when combined with oxide of copper, green,
blue, and red may be obtained; with oxide of
cobalt, a blue; with iron, a brown or orange; with
manganese, a purple; with silver and gold, an
orange red; and with stannic acid or oxide of tin,
an opaque white.

These enamels can be
mixed together in the cru-
cible to obtain any variety
of colour. All of them
are made by the flux and
the oxides fused together
at an even temperature,
and the quality of their
tone is determined by the
intensity of their fusion and
the intimacy of their com-
bination. There is no
limit to the range of colour,
except that vermilion and
lemon yellow cannot be
obtained.

Enamels are either “soft”
or “ hard ”—that is, they
are either easily fused at a
comparatively low tempera-
ture or they require a great
heat. An enamel is perfect
when the combination of
the component parts of the
flux, together with the oxide
of metal, is such that there
is no difference of colour,
opacity, or transparency,
throughout the whole mass.
The best way to determine
whether the combination
is perfect is by dipping a copper rod into the
crucible and withdrawing it with a part of the
enamel sticking to the end; pull out the rod
some distance, so that a fine thread of enamel
may be formed; then pass the thread between
the thumb and finger, and the slightest difference
of surface will be detected throughout its length.
The quality of the colour will also be perceptible.
Now, the harder the enamel the greater the
quantity of silica contained in it, and the greater
the resistance to atmospheric or" chemical action;
the softer the enamel the greater its percentage of
lead and potash, and the more liable it is to be
decomposed by atmospheric influences and chemi-
cal agencies. It is very tempting to use soft
enamels, for at first they look so much more
brilliant, and are so much easier to work with, but
there are dangers to which the harder kinds are
less subject. Thus, when in a state of fusion in
the furnace, dust and foreign matters may injure
them greatly, dulling the surface and destroying their
transparency. The soft kinds of enamel contain
a large quantity of lead, and sometimes of borax

91