China-clay of Cornwall, 99 



In porcelain or china and the coarser variety termed pot- 

 tery, the ingredients are so combined as. to act chemically on 

 each other, the decomposed felspar consisting of a fusible 

 glass of silicate of alumina and potash, more opaque than 

 that formed by the fused silex in which it is disseminated ; 

 and when the body is formed of China-clay, infusible at the 

 highest temperature, in the process of vitrifaction, it is so 

 acted on, as to form a substance uniformly opaque, having a 

 vitreous, waxy fracture, and when coloured by some metallic 

 base is termed stoneware. 



There are two kinds of china or porcelain ; the one termed 

 the hard china was formerly imported from France, though, 

 of late years, it has been altogether superseded by the second 

 variety, or soft china. The body of hard china may be con- 

 veniently formed by a mixture of ingredients in the following 

 proportions : — 



Kaolin, or China-clay 



70 parts 



Felspar 



14 ... 



Sand 



12 ... 



Selenite 



4 ... 



which calcined, forms the biscuit : this, after being dipped in 

 a mixture of potash and felspar, is again heated, when vitri- 

 faction ensues, the article possessing a homogeneous trans- 

 lucent structure, and not a mere glaze or coat as found on 

 the common earthenware. In making soft china the English 

 potters fully vitrify the ware by the first application of heat, 

 the shape of the article being kept by ground flint, removable 

 with ease after it is taken from the oven, and the glaze being 

 subsequently applied is vitrified at a lower temperature than 

 that used in the formation of the biscuit of soft china, the in- 

 gredients used to form which, are, — 



Bone . . . . 46 parts 

 Kaolin . . . . 31 ... 



China-stone . . . 23 ... 



In making the glaze, a frit is first formed, which renders the 

 glaze more easily applicable to the surface of the biscuit, by 

 calcining a mixture similar to the following : — 



G2 



