POTTERY. 233 



and again dried. It is then finely sifted, and most 

 accurately mingled with quartz, ground very fine; 

 to which, then, is added some burnt and finely 

 pulverized gypsum, This mass is worked with 

 water to a paste, and duly kneaded ; it is usually 

 suffered to lie in this state for years. The vessels 

 and other goods formed of this mass, are first 

 moderately burnt in earthen pots, to receive a cer- 

 tain degree of compactness, and to be ready for 

 glazing. The glazing consists of an easily melted 

 mixture of some species of earths, as the petrosilex 

 or chert, fragments of porcelain and gypsum, 

 which, when fused together, produce a crystalline, 

 or vitreous mass, that, after cooling, is very finely 

 ground, and suspended in a sufficient quantity of 

 water. Into this fluid the rough ware is dipped, 

 by which the glazing matter is deposited uniformly 

 on every part of its surface. After drying, each 

 article is thoroughly baked or burned in the violent 

 heat of the porcelain furnace. It is usual to deco- 

 rate porcelain by paintings, for which purpose, 

 enamels or pastes, coloured by metallic oxydes, 

 are used, so easy of fusion as to run in a heat less 

 intense than that in which the glazing of the ware 

 melts. 



Delft-ware, so called because first made at Delft 

 in Holland, is a kind of pottery made of sand and 

 clay, and but slightly baked, so that it resists sud- 

 den application of heat. Articles made of this are 

 glazed with an enamel, composed of common salt, 

 sand ground fine, oxyde of lead, and oxyde of tin. 

 The use of the latter is to give opacity to the 

 glaze. 



Tobacco-pipes require a very fine tenacious, and 

 refractory clay, which is either naturally of a per- 

 fectly white colour, or, if it have somewhat of a grey 



