Porcelain and Earthenware. 257 
as being unchangeable by heat, when prepared with such ingredients, 
as form a flux surround and thus give them protection and brilliancy.* 
Carmine, purple and violet, of the most delicate and beautiful 
shades are obtained from gold; they answer well on enamels, but 
will not endure the heat of the porcelain furnace. Asa fine rose 
color however, and all shades of red are obtained from oxide of iron 
prepared with nitric acid. This oxide is calcined and then fused 
with a flux composed of borax, sand and minium. 
Yellows are produced from the oxide of lead, white oxide of an- 
timony and sand. They may be deepened by red oxide of iron in 
small quantity. 
Blue is derived from oxide of cobalt. The harder and more in- 
fusible the porcelain, to which it is applied, and the greater the de- 
gree of heat, the more intense will be the color. 
Greens may be obtained from the green oxide of copper, and 
from mixing blue and yellow, but will not endure a high heat. 
“Pure chromate of lead gives a beautiful green of great intensity on 
porcelain.” 
Browns are obtained from oxide of iron; and Bustres and Russets 
from manganese, brown oxide of copper, oxide of iron and umber 
earth. 
Black is made by darkening blue, with oxides of manganese, and 
iron. 
Soda and potash are not used as fluxes, because being volatilizing in 
great heat they abandon the colors which will not then adhere to the 
porcelain. Brongniart prefers a flux of glass, lead, and borax; while 
Montamy advises one made of powdered glass, calcined borax, and 
refined nitre. With either of these fluxes, each color is ground in a 
mortar of glass, until perfectly comminuted, when they are fused in 
a crucible until the swelling ceases. ‘The greatest accuracy is re- 
quired in proportioning the relative quantities, that no more of the 
menstruum is employed, than is necessary to reach the point of vitri- 
fication. If too little were used the colors would be dull—if too 
much they would spread, and the fine touches of the artist would 
be lost. After being properly fused, and cooled, they are ground 
for use. When the artist employs the colors, he rubs them on a glass 
palette, with some liquid until they are of a suitable consistence to be 
applied with a hair pencil on the surface of the porcelain. Oil of 
* See Brongniart’s Essay on Colors. 
