CLAYS OF NEW YOKK T93 



Yellow ware and Rockingham ware. These differ from stoneware 

 in that the body is burned first, then glazed and burned again. It 

 agrees with stoneware in being made from natural clays, and with 

 white earthenware, or porcelain, in being burned twice. 



In yellow ware the body is covered with a transparent, easily 

 fusible glaze, while in Eockingham ware the glaze is colored brown 

 or black by the addition of manganese. 



C. C. ware, white granite. These are made of high grade clays, 

 but not the best obtainable, with other materials. The mixture 

 usually consists of kaolin to form the body, ball clay for plasticity, 

 silica to prevent excessive shrinkage, and feldspar to serve as a flux. 



0. O. ware differs from china or porcelain in the quality of the 

 materials used, the clays employed having enough iron to give a 

 slight off color to the ^rare. Attempts are made to counteract this 

 by introducing coloring material into the glaze. 



In white granite or ironstone china the best materials obtainable 

 are used, but the body is not burned to vitrification, and differs in 

 that respect from porcelain. In fact white granite bears the same 

 relation to porcelain that earthenware does to stoneware. A very 

 slight amount of iron will tend to produce a yellowish tint, which is 

 neutralized by adding a small amount of cobalt oxid, that produces 

 a greenish hue far less noticeable. 



The kaolins and sometimes the ball clays have to be purified by 

 a washing process; for the percentage of iron oxid which a kaolin 

 contains should be less than 1^. Even though the clay alone may 

 not show any off tint when burned, the presence of a coating of 

 glaze is sure to bring it out, if the iron is present. The kaolins used 

 in this country are obtained mostly from England, l!^orth Carolina, 

 and Georgia, while the ball clays come from ITew Jersey, Florida, 

 Kentucky and Missouri. 



Quartz and feldspar are obtained from a number of localities, 

 some of them in 'New York. 



