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

58 ENAMELS AND ENAMELLING.
later must also be taken in fusing the enamel masses-,
coloured with this preparation.
By changing the proportions of ferrous sulphate and
aluminium compounds in the mixture different shades of red
can be produced. For instance, 10 parts of ferrous sulphate
and 30 parts of alum, mixed and treated as above, will
furnish a product imparting a handsome flesh tint to enameL
The wealth of colour afforded by the ferric oxide prepara-
tions, combined with their cheapness, places them among the
most valuable and most extensively employed pigments now
used in the enamel industry.
Gold Preparations.
The preparations of gold serving for the production of
purple red shades in enamels and glass masses yield the finest
colours known, though at the same time the manufacture of
the pigments (or rather their incorporation with the enamel
mass)
with in this connection. Formerly, purple of Cassius was
the sole means employed for the preparation of gold reds, but
is the most difficult of all the tasks we have to deal
of late its place is frequently taken by pure gold chloride in
combination with sodium chloride.
Sodium-Gold Chloride.
This product formerly also used in medicine under the
name of gold salt, Sal auri Figuieri, or Aurum muriaticum natro-
natum crystallisatum is prepared in the following manner:
Gold, preferably in the form of gold ducats, which are made
of very pure metal, is placed in a glass beaker standing in a
basin of water, and covered with freshly prepared nitro-
hydrochloric acid aqua regia composed of 1 part
of nitric
acid and 4 parts of hydrochloric acid, the reaction being
assisted by the application of heat to the water bath.
When ducats have been employed no residue is left, the
gold entirely dissolving : but if silver be present,
an insoluble