120 GEOLOGY OF OHIO. 



Preparation of the Clay. More stress is laid on suitable weathering 

 than in the stoneware business. There is but little chemical change 

 involved, merely the physical changes due to exposure. 



The mechanical treatment is by washing altogether; no other pro- 

 cesses are in use so far as is known. The washing is in all respects the 

 same as for stoneware, except that the screens for sifting the pulp are of a 

 much finer mesh — sixty to one hundred mesh instead of forty. 



The pottery processes are largely confined to jolly and mold work; 

 very little hand turning is done. 



In burning small and delicate clay wares, it becomes necessary to find 

 a way to separate the wares into small portions so that the weight of one 

 piece on another shall not deface or bend it. This is accomplished by 

 what is known as saggers. They are variously shaped and sized boxes or 

 cases, made of refractor, open-grained clay ware, which will stand a high 

 heat and much handling. The ware is packed into these saggers which 

 are then set in the kiln until it is filled with these cases piled one on 

 another, the bottom of one forming the cover for the next. Between each 

 a thin coating of clay is put so as to make the saggers airtight or nearly 

 so. The expense of burning in saggers is largely in excess of the direct 

 burning in stoneware. The cost of heating up the large mass of clayware 

 in the saggers on each burn is no slight item. The expense of the labor 

 and material in making them is still more important. In a good sized 

 pottery two or three men are generally kept busy all the time in making 

 saggers. In East Liverpool, there are two or more establishments who 

 do a large business in manufacturing nothing but saggers and other pot- 

 ters supplies. 



The kilns used are the regulation muffle updraft kilns employed in 

 burning all kinds of pottery and described in connection with stoneware. 



In some potteries, however, there are used double decked kilns, in 

 which white, or CC wares are burnt in the lower compartment and the 

 first or biscuit burning of yellow ware in the upper story. This is the 

 same device used by stoneware men to increase the profits, by burning 

 flower pots with the waste heat of the stoneware. This process is a great 

 saving of cost, but in the nature of the case is not as good for the uniform 

 quality of the ware, for where two kinds of ware are burnt in one kiln the 

 burning is bound to be adjusted for perfection of one grade, and the other 

 must take what heat it can get. 



The temperature employed in burning yellow ware is low. Only one 

 opportunity was afforded to measure a kiln of yellow ware at its highest 

 heat. The temperature in this case showed \>y the lunette 1,710 degrees 

 at the top peep-holes and 1,680 degrees at the bottom, or practically 1,700 

 degrees on the kiln. This is about 175 degrees cooler than a stoneware 

 kiln. The trials at this point were light buff and could be scratched with 

 a knife with difficulty. 



