118 GEOLOGY OF OHIO. 



In addition to the tabulated data the total quality of ware actually 

 manufactured in 1891 was made the subject of inquiry and the results 

 collected indicate that the production of the state was very close to 

 13,500,000 gallons, with a value $540,000.00 ; of this quantity the Akron 

 district produced a little over 7,000,000 gallons, the Zanesville district 

 about 4,000,000 gallons, and outside shops 2,500,000. 



The markets reached by Ohio stoneware are only limited by the con- 

 fines of the country. It is shipped to the Pacific coast, and north and 

 south. Some competition has been introduced in the western states, by 

 potteries being located there, but Ohio still manufactures far more ware 

 than any other state in the union. 



(c.) Yellow and Rockingham Wares. 



The technical distinction between stoneware and yellow ware lies 

 in the fact that yellow wares pass through a burning process to develop 

 the body of the clay, and a second firing to develop the glaze which is 

 put on after the first or biscuit burning. In this respect the yellow ware 

 process is exactly like the processes used in the higher grades of pottery, 

 while it resembles the manufacture of stoneware in being composed of 

 natural clays entirely. 



The yellow ware is glazed with a clear glaze, composed largely of 

 lead oxide, which developes and adds luster to the natural buff color of 

 the clay. 



The Rockingham wares are glazed with a similar glaze brown or 

 black by the addition of manganese ; this is either applied solid or spat- 

 tered over the yellow glaze in blotches. 



The clays tor yellow wares should be very plastic, smooth, potters 

 clays, free from impurities or fine specks, with enough iron to give a fair 

 color to the ware. 



They need not be refractory, as the heat used in glazing is low, and 

 the intention is only to burn the clay to its best plrysical strength. In a 

 general way, any good stoneware clay will make good yellow ware but 

 the converse of this assertion is not true. 



