Porcelain and Earthenware. 249 



one fifth to one third and lime from one five hundredth to one two 

 thousandth part. Iron, from the minutest trace to twelve or fifteen 

 per cent, is found in the more common wares, but not in the perfect- 

 ly white porcelains. Another substance called hoache is used for 

 a fragile, light, but very beautiful ware. It is employed for glazes, 

 and, with some other ingredients, makes a splendid enamel. 



The two famous materials employed by the Chinese are kaolin and 

 pe-tunt-se. Reaumur found by analysing them, that they were com- 

 bined in the following proportions, kaolin consists of silex 74, alu- 

 mine 16.5, lime 2, and water 7. Petuntse contains of silex 74, alu- 

 mine 14.5, lime 5.5. 



The substitute in Europe for petuntse, is calcined flint : and de- 

 composed felspar for kaolin, the lime or potash being adjusted by art; 

 whereas in the Chinese the alkali is an ingredient in the native com- 

 pound. The difficulty of adjusting large masses, where success de- 

 pends on the accuracy of the nicest chemical tests, makes it obvious, 

 that art can scarcely hope to equal that, which is done in the great 

 laboratory of nature. Clays of tolerably good working quality are 

 found in several parts of Europe, similar to, although not identical 

 with those of China and Persia. 



Magnesian clays obtained from steatite, have been employed of 

 late /ears in the composition of porcelain. A small amount of it 

 with other clays limits the contraction of wares. 



III. Processes employed. 



ft 



f 



The first operation is that of mixing the clay with pure water to the 

 consistence of cream which is effected in vats, by long wooden instru- 

 ments, which the men move backwards and forwards forcibly through 

 the whole mass. It is is called blunging, and is an operation of great 

 labor. The flint is prepared in the same manner, but in a separate 

 cistern. The grosser parts soon subside, and the finer are drawn off 

 and mixed by measure; the specific gravity of each previously as- 

 certained ; the standard being twenty four ounces the wine pint for 

 the clay, and thirty two ounces the wine pint for the flint. When 

 the clay and flint are mixed in suitable proportions, the whole mass, 

 in a semi-fluid state, is passed through sieves made of the finest silk 

 lawn, in order to detain any particles that had not been sufficiently 



