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

72 ENAMELS AND ENAMELLING.
When a preponderating quantity of ferric oxide is used,
the fused enamels will exhibit a decidedly reddish tinge (flea
brown) ; the addition of a yellow pigment will produce a
yellowish brown, and so on.
BLACK PIGMENTS.
Although no direct black pigment for enamel is known,
black enamels are easily prepared by employing some powerful
metallic oxide, such as ferric oxide, cupric oxide, cobalt oxide,
or manganese dioxide, in larger proportion than usual.
Each of the aforesaid oxides produces a characteristic
colour, but when the amount taken is considerable the
coloration becomes so intense as to appear black. Never-
theless a comparison between two such black shades produced
by, say ferric oxide and manganese dioxide respectively, will
show decided differences in tone. However, to obtain an
absolutely pure velvet black all that is necessary is to mix
the said oxides together and fuse them with the enamel, the
various individual shades being thereby neutralised and con-
jointly furnishing a pure black.
It is evident that in the case of enamel masses intended
to be coloured in dark shades or black no particular care need
be taken over the purification of the raw materials, the yellow
tinge due to impurities being completely masked by the
darker colour.
On the other hand, the contrary is the case when enamels
are to be obtained pure white or in delicate shades ; and in
such event special artifices and adjuncts must be resorted to in
order to attain a maximum degree of colourlessness in the
mass, since it is only under these conditions that the full
beauty of the superimposed colour can be brought out.
Consequently, every enamel mass intended for artistic purposes
must be subjected to a process of decoloration.