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

PIGMENTS. 59
sediment of silver chloride remains behind. The solution is
poured oft' with care, and is evaporated to dryness in a
porcelain basin at a gentle heat.
Pure sodium chloride, in quantity equal
to one- fourth the
original weight of gold taken, is added to the dry residue
and the whole is then dissolved in water and re-evaporated to
complete dryness.
Tin-Gold Chloride.
Nowadays the use of purple of Cassius for producing red
on enamel is superseded by a compound chloride of tin and
gold. This is prepared in exactly the same manner as the
double salt of gold and sodium just described, except that
after the gold chloride solution has been evaporated to
dryness
it is re-dissolved in water and mixed with a solution
of tin chloride. A precipitate of tin-gold chloride is thrown
down, which, after being collected on a filter and washed
with pure water, is dried by gentle heat.
Purple of Cassius.
The substance known under this title is difficult to prepare,
and its properties and colour differ according to the method
of preparation adopted, a true gold purple of Cassius being
formed only when a solution of gold chloride is brought into
contact with a liquid containing both stannous chloride and
stannic chloride.
Out of the numerous existing recipes for obtaining this
preparation the following
are known to be reliable :
Light Purple.
According to Wachter a light shade of gold purple can be
obtained by the use of the solution of stannic chloride prepared
by dissolving 5 grams of pure tin in boiling aqua regia,
evaporating this solution to dryness on the water bath, and
re-dissolving the mass in distilled water. On the other hand, a