396 Researches respecting the 
mel on that which is raw, and the artist may afterwards 
finish with the tender colours. The colours applied on 
the raw material do not require any fiux; there is one, 
even, to which silex must be added, that is, the calx of 
copper, which gives a very beautiful green : but when you 
wish to employ it on the raw material, you must mix with 
it about two parts of its weight of silex, and bring the 
mixture into combination by means of heat. You after- 
wards pulverise the mass you have thus obtained, in order 
to employ it. 
To obtain good white enamel, it is of great importance 
that the lead and tin should be very pure. If these 
metals contain copper or antimony, as is often the case, 
the enamel will not be beautiful : iron is the least 
hurtful. 
Of Coloured Enamels. 
All the colours may be produced by the metallic 
oxyds. These colours are more or less fused in the fire, 
according as they adhere with more or less strength to 
their oxygen. All metals which readily lose their oxy- 
gen cannot endure a great degree of heat, and are unfit 
for being employed on the raw material. 
Purple. 
This colour is the oxyd of gold, which may be pre- 
pared different ways ; as by precipitating, by means of a 
muriatic solution of tin, a nitro-muriatic solution of gold 
much diluted in water. The least quantity possible of 
the solution of tin will be sufficient to form this precipi- 
tate. The solution of tin must be added gradually until 
you observe the purple colour begin to appear : you then 
stop 5 and having suffered the colour to be deposited, you 
