ENAMELLING. 
Concerning the Red, Rose, and Brown Colours, 
obtained from Iron. 
These colours are made from red oxydat- 
ed iron, prepared with nitric acid. The 
oxides are calcined still more by expos- 
ing them to the action of fire. If too much 
heated they change to a brown. 
Their flux is composed of borax and 
minium in small quantity. 
These are the oxides which afford the 
rose and red colours, which may be substi- 
tuted instead of the same colours made 
from oxide of gold. If properly applied on 
hard porcelain they never change. Brong- 
man made roses with these colours, and there 
was no difference between the flower before 
and after baking, except the brilliancy which 
colours naturally receive from fusion. 
The colours may either be previously 
fused or not, at pleasure. 
In a violent fire, they either partly dis- 
appear, or produce a dull and brick-dust 
red colour, which is not at all agreeable. 
Their composition is the same, either for 
tender porcelain or for glass. They do not 
change on the latter, but on the former 
they almost entirely disappear by the first 
fire ; and they must be laid on very heavily 
in order to have any part visible. 
It is to the presence of lead in their glaze 
that this singular effect must be attributed. 
Brougman ascertained this by a very simple 
experiment. He placed this colour on win- 
dow glass, and fired it very strongly and it did 
not change. He then covered some parts Of 
it with minium, and again exposed it to the 
fire. The colours totally disappeared in 
those places where the red oxide of lead 
had been applied. When this experiment 
was performed on a larger scale, in a closed 
vessel, a large quantity of oxygen gas was 
disengaged. 
This observation seems clearly to prove 
the effect of oxyded lead as a discolourer of 
gdass. We see that it does not operate as 
has been supposed, by burning combustible 
impurities in the glass, but by dissolving, 
discolouring, and volatilizing the. oxide of 
iron, which may effect its clearness. 
Concerning the Yellows. 
Yellows are colours which require much 
precaution in fabricating, on account of the 
lead they contain ; which, sometimes, by 
approaching to the metallic state produces 
black i pots. 
The yellows j pf hard and tender porcelain 
are the same. They are composed of oxide 
of lead, white oxide of antimony, and sand. 
Oxide of tin is sometimes added ; and 
when it is required very lively and resem- 
bling the colour of marigold, red oxide of 
iron is added, the very deep colour of which 
disappears during the previous fusion they 
undergo, on account of the lead contained 
in this yellow. When these colours are 
once made they do not change ; they dis- 
appear almost entirely in the porcelain fire- 
yeilows. 
These cannot be applied to glass, they 
are opaque and muddy. That employed 
by the ancient painters on glass is, on the 
contrary, beautifully transparent, very bril- 
liant, and of a colour approaching gold. 
The processes they give indicate, that it 
contains a mixture of silver ; but when ex- 
actly followed they afford nothing satifac- 
tory. Citizen Meraud succeeded in making 
it as beautiful as the ancient painters on 
glass, by employing muriate of silver, oxide 
of zinc, white clay, and the yellow oxide of 
iron. These colours are applied to glass 
simply ground and without flux. The 
oxide of iron gives the yellow nearly the 
same tinge as it ought to have after the 
baking, and contributes, with the clay and 
oxide of zinc, to decompose the muriate of 
silver without disoxydating the silver itself. 
A powder remains after baking which does 
not penetrate the glass, and may be easily 
cleared off. 
This yellow when employed in greater 
quantities affords deeper shades, and pro- 
duces a reddish colour. 
Concerning the Blues. 
These are known to be obtained from 
the oxide of cobalt; their preparation is 
known to every chemist. The superiority 
at Sdvres, so justly reputed for the supe- 
riority of its blues, is owing merely to the 
care taken in its fabrication, and to the 
quality of the porcelain, which appears 
more proper to receive it on account of 
the violent fire it can support. 
Brougniart observed one fact respecting 
the oxide of cobalt, which is, perhaps, not 
known to every chemist. It is volatile in a 
Violent heat ; to this property must be at- 
tributed the bluish tint which the white 
(bordering upon blue) always receives. 
A white piece was purposely put in the 
same case next to a blue, the side of the 
white piece which was turned towards the 
blue became very bluish. 
The blue of hard porcelain, prepared for 
what is called a blue ground by strong fire, 
