4M POTTERY AND PORCELAIN. 



terwards, it is on'y in a few districts that clays are to be found that 

 retain a perfect whiteness. Tims there exists at the foot of a range 

 of high liiils that directly overlook the Staffordshire potteiie-, a 

 Strain .11 of \vi ite day lo appearance fully equal if no( superior to 

 the best Devonshire Hays, which cannot be en ployed for fine 

 pottery from its acquiring in burning a yellowish cream colour 

 vhich no art can correct. This colour is supposed to depend on 

 an inter. i ixture of iron. 



The fusibility of clays and of other pottery earths is a subject of 

 extreme importance, as it is this prop* rty that principally consti. 

 tutes the difference between common pottery and porcelain. 



We have delim d porcelain to be a species of pottery ware com- 

 posed of an earthy mixture which resists complete fusion in a very 

 considerable heat, but has been brought b) a less heat than its 

 melting point to a state of incipient fusion, and is thereby rendered 

 extremely hard, sonorous, and semi-transparent, and posses 

 semi conchoidal splentery fracture approaching to the vitreous, 

 which is completely conchoidal. This last i> quite a distinctive 

 charactt r between porcelain and pottery, for the fracture of pot. 

 tery is extremely granular : and hence porcelain may correctly 

 be regarded as a substance of a middle nature between pottery and 

 glass. 



From these circumstances it appears probable that no chemical 

 action takes place in any pottery combination till it arrives at the 

 state of porcelain. The most perfect and b-auiilul porcelains of 

 Japan in China are composed of two distinct earths ; one in which 

 silex predominates, and which units in a strong fire ; and another 

 which is infusible per se : and by the union of those two earths a 

 porcelain is product d which scarcely vitrifies at the utmost furnace 

 heat which art can excite. This substance possesses ti>e combined 

 exce'lHieies of ^reat hardness, beautiful semi. transparency, exqui- 

 site whiteness, where not artificially coloured, strong fou_ 

 and cohesion ; so that it has strength enough for the purposes for 

 whit h ii is designed when n.ade very thin, and bears sudden heat- 

 ing and coo'ing without cracking. 



Of V beautiful European porcelains which have been made in 

 imitation of tin- oriental, it does not appear that any of them unite 

 all iis excellencies. Earthy combinations have been made qua ly 

 strong, tough, an.) in.u ible,and as truly porceluincous when burnt, 

 but they have not quite rivalled the best Japanese in delicate 



