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

III.
KAW MATERIALS FOR THE MANUFACTURE OF
ENAMELS.
The raw materials worked up into enamel are numerous
a-nd diverse in character, the production of the various
coloured enamels necessitating the employment of many
substances not generally used for glass-making. They may
all, however, be divided into two main classes : the general or
fundamental materials, essential to every enamel ; and the
particular substances required to impart certain definite
qualities fusibility and colour to special kinds of enamel.
The first class may be termed fundamental, and the second
supplementary, materials; a third class, of subsidiary^materials,
comprising certain substances used in applying the enamel,
though not in the actual process of manufacture.
FUNDAMENTAL MATERIALS.
Since, as has already been stated, enamels should be
reckoned as being in the same category with glass, it follows
that their production necessitates the use of the same materials
as are used in glass-making.
Ordinary glass consists, as mentioned above, of soda, lime
and silica, or potash, lime and silica, or of mixtures of these sili-
cates, lead silicate, in addition, forming an important constituent
of many kinds such as the so-called flint glass and crystal
glass. The small, though inevitable, proportion of extraneous
impurities such as ferric oxide, may be dismissed from con-
sideration as merely accidental, especially in fine white glass.