96 GEOLOGY OF OHIO. 



The oxygen ratio of this clay being calculated, shows it to be : 

 Oxygen in silica : Oxygen in bases : : 34.72 : 11.52 or 3 : 1 

 or that the clay in fusion is practically a trisilicate. 



The extremes from this average are found to be three pounds and ten 

 pounds. No. 3 is the sandiest clay of the lot, showing: 



Clay base 48.27 



Sandy Matter 45.91 



Impurities (by dif.) 4.80 



Water 1.97 



100.00 

 Oxygen ratio, acid : base : : 2.66 : 1 



This clay is used in making cooking pottery which differs from or- 

 dinary stoneware in that it must be open and loose in structure to rapidly 

 convey the heat through its body, and allow rapid expansion and contrac- 

 tion, and it depends on the glazes entirely for retention of its fluid contents. 



No. 10, the opposite extreme of the series, is a clay used in making a 

 fair article of stoneware. It is what is called a tender clay or, in the 

 language of stoneware men, it is not "safe." The slightest excess of heat 

 results in the ruin of some ware and extra precautions have to be adopted 

 in cooling it down, to prevent cracking. The defects are such as to afiect 

 the pockets of those who make it rather than those who buy the mar- 

 ketable ware. 



The trouble lies in its readily fusible nature. Clays used in glazing it 

 have to be softened with lead or borax and even then though a beautiful 

 glaze is produced there is very little margin between melting the glaze 

 and sagging the ware. 



The chemical character of this clay shows the reasons for this con- 

 dition of affairs. 



Clay base 66.50 



Sandy matter 24.11 



Fluxing matter 6.56 



Water 2.48 



99.65 

 Oxygen ratio, acid : base : : 2.15 : 1 

 or,but little over the bi-silicate ratio. 



The preparation of clays for use in the stoneware pottery is accom- 

 plished in two different ways, (a) by grinding, {b) by washing. Each 

 process is specially adapted to the preparation of clay for certain shapes 

 and sizes of ware and also to different kinds of ware. 



Many well equipped stoneware shops contain both a washing and a 

 grinding plant in order to avail themselves of the advantages of each 

 kind of clay. 



In the Akron district a number of the smaller firms have united to 

 build a washing plant at the clay mines, some five miles from the fac- 



