SAND — CLAY. 373 



palpable powder The kaolin is mixed with a certain pro- 

 portion of feldspar, flint and lime. The whole are worked 

 up together in water, by mallets and spades, and well knead- 

 ed by the hands and sometimes the feet of the workmen. 

 The plastic material is thon laid aside in masses of the size of 

 a man's head, and kept damp till required ; the dough, as it is 

 called, is now ready for the potter's lathe, (or other means, x 

 by which it is moulded into the various forms of china ware. 

 After moulding, they are slowly and thoroughly dried, and 

 then taken to the kiln, for a preliminary baking. They come 

 out in the state of biscuit, and are ready for painting and 

 glazing. The colors are metallic oxyds, which are put on 

 either from a wet copper-plate impression on bibulous paper, 

 or by means of a brush. The former is used for flat sur- 

 faces ; the paper is rubbed on carefully to transfer the im- 

 pression to the porcelain, and is then wet and washed off. 

 It is then carefully heated to evaporate any oil or grease em- 

 ployed in the printing. The glaze is made of a quartzose 

 feldspar ; it is ground to a very fine powder and worked into 

 a paste with water, and a little vinegar. The articles are 

 dipped for an instant into this milky fluid, and as they absorb 

 the water they come out with a delicate layer of feldspar in 

 a dry state. They are touched with a brush wherever not 

 well covered. They are then ready to be finally baked in 

 the kiln, for which purpose each vessel is placed in a sepa- 

 rate baked clay case or receptacle, called a sagger. In this 

 process the material undergoes a softening, amounting al- 

 most to a partial fusion, and thus receives the translucency 

 which distinguishes porcelain from earthen or stone ware. 



The blue color of common china is produced by means 

 of oxyd of cobalt ; carmine, purple and violet, by means of 

 chlorid of gold ; red of all shades by oxyd of iron ; yellow 

 by oxyd of lead, or white oxyd of antimony and sand ; green 

 by oxyd of copper or carbonate of lead ; brown by oxyd of 

 iron, manganese, or copper. A steel luster is produced from 

 chlorid of platinum. 



The best Sevres ware is made from 63 to 70 parts of 

 kaolin, 22 to 15 of feldspar, nearly 10 of flint, and 5 or 6 of 

 chalk. In China the kaolin is mixed with a quartzose feld- 

 spar rock, consisting mainly of quartz, called peh-tun-tsz. 



Soapstone is sometimes used in this manufacture ; and as 

 :t substitutes magnesia for a part of the potash, it makes r. 

 harder ware : but it is also more brittle. 



