256 Porcelain and Earthenware. 



bodies on which they are laid ; and the result is that they crack and 

 peel off and not only is the ware defaced, but becomes permeable 

 by fluids, is useless, and perhaps falls to pieces. 



Soft porcelain was made at Bow and Chelsea, in England, and 

 at the Sevres works, before the disclosures of D'EntrecolIes. " It has 

 for its base" says M. Brongniart, "a vitreous frit rendered almost 

 opaque, and susceptible of being worked with clay, and is glazed 

 with an exceedingly diaphanous glass, into which there enters a great 

 deal of lead." It is very white and approaches the condition of 

 enamel, which according to the same authority is " glass made opaque 

 by the oxide of tin and rendered fusible by the oxide of lead." 



The vitreous frit alluded to above consists of one part pure clay, 

 three parts of a compound of nitre, soda, alum and selenile, with a large 

 proportion of sand and a little common salt. Another and better rule 

 assigns nine parts prepared flint, nine parts fragments of porcelain 

 ground to powder, four parts calcined gypsum, and one hundred 

 parts porcelain clay. Arsenic was formerly used at Sevres, for some 

 of the work, but the government has ordered a discontinuance of 

 that branch of manufacture. Soft porcelain is very beautiful, and 

 in the painting and brilliancy of colors the most perfect specimens 

 are scarcely inferior to the Saxon or Chinese; but it does not pos- 

 sess the gem like solidity, fineness and translucency, with the almost 

 velvet surface of the genuine pieces of those admired manufactures. . 



Stone ware is a very perfect kind of pottery, approximating in 

 density and infusibility, to the character of porcelain. When prop- 

 erly made, it will strike fire from steel. Vessels containing sixty im- 

 perial gallons are made of this ware, and are found very useful in 

 the arts. 



Lustre ware is produced by giving the surface a metallic covering. 

 This is effected after the vessels have been glazed and baked in the 

 gloss oven, by mixing the oxide of a metal levigated to a fine pow- 

 der with some one of the essential oils, and this mixture is then 

 brushed over the surface. They are then taken to the enamelling 

 kiln, where " the heat dissipates the oxygen, and restores the metals, 

 to their metallic state." Platina produces a lustre resembling pol- 

 ished steel. Gold lustre is of a dark greenish yellow color. 



Of Colors. — Those colors employed in painting on porcelain, 

 which will endure the heat of the furnace, are obtained only from 

 metallic oxides. M. Brongniart, describes these verifiable colors 



