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

62 ENAMELS AND ENAMELLING.
and yellow-forming pigments together in suitable proportions'.
Success is, however, certain only when a preparation of
antimony is used along with the red iron pigment (ferric
aluminate) ; gold compounds are unsuitable, being too readily
converted into metallic gold.
The resulting shade of orange obtained varies from orange
yellow, when the antimony preparation preponderates, to a
redder tinge when the conditions are reversed.
GREEN PIGMENTS.
Green enamel may be prepared in various ways :
by
in-
corporating certain metallic oxides with the enamel mass, or
by adding to the latter a mixture of pigments producing blue
and yellow colours respectively. As, however, in this latter
method the resulting shade of colour is less under control,
besides being more troublesome, the direct process is generally
adopted.
The oxides capable of colouring enamels green, are, ferrous
oxide, cupric oxide and chromic oxide. Each of these develops
its own particular shade of green, ferrous oxide yielding " bottle
green" (the colour of common green glass), whilst copper and
chromium furnish emerald shades of different kinds readily
distinguishable by comparing glasses tinted with these oxides.
Ferrous Oxide.
Owing to the inferior green developed by ferrous oxide,
and the difficulties encountered in producing the colour, this
substance is seldom used for colouring enamels. The author
has, however, found that a very handsome shade is obtained
provided the ferrous oxide be used in a perfectly pure state,
the depreciation of the colour being occasioned by the presence
of other metals, more especially manganese and copper, as well
as by ferric oxide.
Ferrous oxide cannot be used as such, because when pre-