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

60 ENAMELS AND ENAMELLING.
solution of stannous chloride is prepared by dissolving tin in
hydrochloric acid, the metal being in excess. This solution is
concentrated to a density of 1'7, and 2 grams are then added
to the stannic chloride solution, the whole being diluted with
10 litres of water.
To this liquid is added a solution of gold chloride (prepared
by dissolving 0'5 gram of gold in aqua regia, evaporating to
dryness and re-dissolving in water), the whole being stirred
thoroughly and treated finally with 50 grams
of ammonia.
The greater part of the liquid is decanted from the resulting
precipitate, and the latter is then collected on a filter, washed
quickly, mixed with 20 grams of lead flux whilst still moist,
and finally dried.
This lead flux is compounded of a mixture of 2 parts of
red lead, 1 part of quartz and 1 part of calcined borax.
The resulting preparation is amethyst in colour but may
be converted into true purple by adding to it, when dry, 3
grams of dry silver carbonate prepared by treating a solution
of silver nitrate (lapis infernalis) with sodium carbonate so
long as a precipitate continues to form; then washing the
latter and drying it.
Dark Purple.
To prepare a dark purple, a solution of 0'5 gram of gold
is diluted with 10 litres of water and mixed, by continuous
stirring, with 7 '5 grams of stannous chloride solution (sp. gr.
J.7) and a few drops of sulphuric acid. The moist precipitate
is mixed with 10 grams of lead flux and 0'5 gram of silver
carbonate.
Rose Purple.
Rose purple is obtained by dissolving 1 gram of gold in
aqua regia, and mixing this solution with a solution of 50
grams of alum in 20 litres of water, and 1*5 grams of stannous
chloride (sp. gr. 1*7), ammonia being then added so long as