INGENUITY AND LUXURY 



England, and several other European countries, as 

 well as in certain places in America. As it contains 

 many impurities wherever found, it must be washed 

 before being used for making pottery. This is done 

 by adding large quantities of water until a thin "so- 

 lution" is made, when the impurities, which are heavier 

 than the kaolin, settle to the bottom. The lighter 

 particles of the clay may then be run off. 



It is a peculiar characteristic of this clay that the 

 commoner qualities are the more plastic and require 

 less care in handling than the finer grades. None of 

 them are as plastic as the ball clay, however, but they 

 contain very little of the objectionable iron. This 

 clay is used in the pottery to strengthen it against 

 heavy weights and sudden changes of temperature, 

 as well as to increase its whiteness. Muspratfs analy- 

 sis shows it to contain substances in the following 

 proportions: 



Silica 45.52 



Alumina, with a trace of oxide of iron 40 . 76 



Lime 2.17 



Potassia, with trace of soda i .90 



Magnesia, phosphorus (traces) , and sulphuric acid (traces) 



Water, with small quantity of organic matter 9-65 



For the glass-forming materials used in the body 

 of the earthenware, as well as in the glaze, a granite 

 in which the felspar is incompletely decomposed and 

 which is still fusible because of the presence of alka- 

 line silicates, is used. It is called china-stone, or Cornish 

 stone, since the English supply comes from the hills of 

 Cornwall. It is rich in silica (about 73 per cent.) but 

 contains also about 18 per cent, of alumina with 



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