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. As a 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 Bistres 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. 



