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

PIGMENTS. 61
a precipitate continues to form. The precipitate is washed,
mixed with 70 grams of lead flux and 27 grams of silver
carbonate, and dried.
There are many other recipes for preparing gold purple,
but in all of them the rule applies that, to obtain a good
colour, the solutions employed must be very dilute. It should
also be observed that the colour of the preparations themselves
is no criterion of that imparted by them to enamel, an ugly
brown-red purple often producing the most beautiful shade,
whilst a bright-looking preparation may yield shades the
reverse of handsome.
The quantity of gold purple, or other gold preparations,
required to produce intense coloration of the enamel, is very
small, gold being characterised by a specially high pigmentary
power.
Owing, however, to the trouble involved in its preparation
and the irregularity of the results obtained, gold purple is
going out of use as a pigment for glass, porcelain and
enamels, and is being supplanted by tin-gold chloride, or by
the double chloride of gold and sodium.
Cuprous Oxide.
A purple red, equal in beauty to that obtained from gold
oxide. Unfortu-
compounds, is produced in glass by cuprous
nately, however, this substance cannot be used for enamels,
owing to the readiness with which it is converted into cupric
oxide during the repeated meltings necessary in the case of
these preparations.
As cupric oxide produces a bluish-green
colour in glass the results are, therefore, liable to be erroneous.
ORANGE PIGMENTS.
No single preparation capable of producing an orange
shade in enamel is known ; but, as this colour is a mixture of
red and yellow, it can be prepared by mixing red-forming