PORCELAIN. 



441 



There are various clays pipe-clay, for instance, which is white ; potters' clay 

 is coarser. There is porcelain clay as well as porcelain earth, of which 

 more belo\v. Yellow ochre and sienna are clays used by a-rtists. Bole is a 

 reddish clay ; and tripoli is employed for polishing. There are, besides, 

 andalusite, or chiastolite and disthene, crystalline forms of clay. 



Porcelain has been known to the Chinese for centuries. In 

 1701 it was discovered in Germany by Bottcher, a chemist, who while 

 endeavouring to make gold by Royal command, found the porcelain, and 

 was thereby enriched. Porcelain earth is frequently found ; is known in 

 many places as kaolin, and usually comes from the decomposition of 



Fig. 465. Porcelain furnace. 



felspar. But in Cornwall we find it as decomposed granite, and the filter- 

 ing process can be viewed from the railway, while both gneiss and granulite 

 have been known to yield kaolin. It is also found in China, Saxony, and 

 France. It is free from iron, and when ground and mixed with silicic acid, 

 it is handed to the potter or moulder. After the vessels have been dried in 

 the air they are put into the kiln, and then become white and hard. After 

 that they are glazed in a mixture of porcelain earth and gypsum, or ground 

 flints and oxide of lead, made fluid with water in the glazing of earthenware. 

 The vessel is then put into the furnace again, or " fired," as the process is 

 called, and then comes out white, hard, and partly transparent. 



Earthenware utensils are made of a coarser material, clay and 



