116 GEOLOGY OF OHIO. 



will cost $1,000 to $1,350, well built and of good fire brick in all the essen- 

 tial parts. 



2. Repairs are heavy, if the materials are not first-class. If the best 

 fire brick are used in the beginning, they will be light. Repairs are 

 expensive, owing to the shape of the fires and flue system under the kiln 

 floor. 



3. Fuel. This kiln undoubtedly uses more fuel to the one thousand 

 gallons than the downdraft. A comparison between the two kilns could 

 not be had. 



4. The convenience of setting and drawing are not equal to the 

 downdraft kilns, owing to the interference of the central chimney. 



5. The safety of the burning is the strongest feature of the kiln. 

 With any reasonable care there is no need of any loss, while a downdraft 

 kiln is hardly ever burned off without the rejection of more or less dam- 

 aged ware. 



In one works in the state there are three kilns in use: One square, 

 Akron kiln of six thousand gallons capacity, one round downdraft of 

 eight thousand gallons capacity, and one sixteen foot muffle of three 

 thousand gallons common capacity. The manager of the works placed 

 himself on record, as follows : 



The best kiln, all things considered, the round downdraft. 



The hardest to burn, the Akron kiln. 



The easiest to burn, the Muffle. 



The safest kiln, the Muffle. 



The most expensive, high fuel and slow production, the Muffle. 



The old-fashioned updraft kilns are not important as a commercial 

 factor in the business and are dropping out of use. They are used for 

 producing salt glazed ware in factories where the muffle is used for the 

 black glazed articles. In the smaller and outlaying potteries these old 

 updrafts are still the only reliance. 



The cooling and annealing of stoneware after the burning is finished, 

 offers no special difficulties. It occupies from two to three days, accord- 

 ing to the weather. The critical point in cooling is when the ware is at 

 a black heat, just below redness. The kiln can be left open for several 

 hours until the kiln begins to look dark red. Every air inlet at the bot- 

 tom of the kiln is then shut up tight, and daubed with mud, and the vent 

 holes in the crown are opened so that what little draft gets into the kiln 

 passes out upwards. The connection to the stack is broken soon after 

 the fires are shut down. 



The cost of manufacturing stoneware was approximately obtained in 

 several places in each important district. The following figures represent 

 the average of five estimates, prepared by five stoneware men, independ- 

 ently : 



