PORCELAIN. 31 



Oschatz, examined the products microscopically. The result 

 ^vas a refutation of the usually received opinion that porcelain 

 is a mere mixture of fused feldspar and unaltered kaolin, the 

 latter of which is the cause of its opacity; for it was shown 

 that it consists of a glassy mass, filled with an infinite number 

 of minute needle-shaped crystals, which produce the opacity 

 of porcelain. 



Wilson's analysis of Berlin porcelain gave the following 

 results : 



Silica 71.34 



Alumina 23.76 



Oxide of iron 1.74 



Lime 0.57 



Magnesia 0.19 



Potassa 2.00 



99.60 

 Couper has published a series of analyses of the materials 

 and products of English potteries, in Phil. Mag. (3) xxxi. 435, 

 to which we refer for details. 



Yelloiv Flux for Porcelain Colors. — Salvetat's analysis of 

 such a flux from Sevres, led him to make a similar one of the 

 following composition : 88 pts. gray flux, 3| pts. oxide of zinc, 

 7 pts. hydrated peroxide of iron, and 1| pts. binantimoniate 

 of potassa. The zinc is prepared in the dry way, and the 

 gray flux consists of 22 pts. sand, 11 pts. fused borax, and %Q 

 pts. red-lead. The substances are finely powdered, fused 

 twice and cast out on an iron plate. It facilitates the fusion 

 of colors and gives them body without altering their tone, as 

 it is itself very pale. 



Aventurine Crlaze for Porcelain. — "VVgechter (Liebig's An- 

 nalen, 1849 ; Amer. Journ. 2d ser. viii. 440, and Chem. Gaz. 

 1849) proposes the following enamel for porcelain, in which 

 the golden iridescence is produced by a crystalline separation 

 of oxide of chromium from the brown ferruginous mass of the 

 glaze ; 



