*$0,J Researches respecting the 
it succeeds it is very beautiful, and lias a great deal of 
splendour. By employing the calx of copper alone for 
the processes above mentioned you will obtain, when you 
succeed well, a red similar to the most beautiful carmine. 
The calx of iron changes the red into vermilion, accord- 
ing to the quantity added. If we had certain processes 
for making this colour, we should obtain all the shades of 
red from pure red to orange, by using, in different propor- 
tions, the oxyd of copper and that of iron. The calx of 
copper fuses argil more easily than silex : the case is the 
same with calx of iron. If you fuse two or three parts 
of argil with one of the oxyd of copper, and if the heat 
be sufficient, you will obtain a very opake enamel, and of 
a yermilion red colour ; the oxyd of copper passes from 
red to green through yellow ; so that the enamel of cop- 
per, which becomes red at a strong heat, may be yellow 
with a weaker heat. The same effect may be produced 
by deoxydating copper in different degrees : this will be 
effected according as the heat is more or less violent. 
The above composition might, I think, be employed to 
give a vermilion red colour to porcelain. The heat of the 
porcelain furnace ought to be of sufficient strength to pro- 
duce the proper effect. 
The calx of iron fused also with argil in the same pro- 
portions as the calx of copper, gives a very beautiful 
Wacko These proportions may, however, be varied. 
Blue . 
Blue is obtained from the oxyd of cobalt. It is the 
most fixed of all colours, and becomes equally beautiful 
with a weak as with a strong heat. The blue produced 
by cobalt is more beautiful the purer it is, and the more it 
is oxydated. Arsenic does not hurt it. The saline 
duxes which contain nitre are those best suited to it: you 
add a little also when you employ that flux which eon- 
