CLAY WORKING INDUSTRIES. 115 



the round kiln from all sides than it is to the middle of a square kiln from 

 both ends. 



3. The round kiln is thought by some to be safe on small wares but 

 not safe on thick sections, as the temperature rises too much alike all over 

 the kiln and gives no place of an especial security for the large pieces. 



4. The round kilns are certainly harder to set and draw. 

 Downdraft kilns of the two kinds are thus seen to be the mainstay 



of the Akron district. 



It is claimed that it is entirely possible to burn a kiln containing 

 nothing but black glazed ware in a downdraft kiln, which has been used 

 previously as a salt glaze kiln — and that the results are good. No 

 instance was found where this was being done. 



The Muffle Updraft Kiln is the commonest kiln in use in the pottery 

 trade. All the yellow, white and china pottery in the country is burnt 

 in it. Its adaptation to the stoneware potteries originated with a firm of 

 Pennsylvania potters, who had been in the yellow ware business and took 

 some of their old ideas and appliances with them. Its use in Ohio was begun 

 about six years ago by the Zanesville Stoneware Company, of Zanesville. 

 It has become the main kiln of the Zanesville district. 



In construction it consists of a circular bench containing the fire 

 places which are equally spaced around the center. Each fire place, 

 which is a regular inclosed furnace, with iron doors, delivers its heat 

 partly to an inside pocket and partly through a horizontal flue to a cent- 

 ral stack. The kiln proper is built on top of the fire bench. It is round 

 and tapers to a small diameter about twenty-five feet above the floor. An 

 arched crown, with numerous perforations, is sprung across the inside 

 about eight feet from the floor. The bags run up within a foot or so of 

 this crown, and the central stack runs through the crown and assists to 

 support it. A door affords access on the level of the floor, which is solid. 



In operation the kiln is filled with ware up to the level of the top of 

 the bags and the heat is, therefore, entirely by radiation from the bag 

 walls, the central stack and the floor, which is heated by the radial flues 

 uniting at the center. The gases from the fires do not come into contact 

 with the ware at all, except on the topmost course and then but slightly. 



Such a kiln, it will readily be seen, is slow to heat up and slow to 

 cool — sudden changes in the fires cannot affect the ware quickly and 

 there is, practically, no reducing action from the fires. 



These kilns are especially adapted to the production of slip glazed 

 ware, either black, red or white; they are useless for salt glazing. There 

 are several works in the Zanesville district which do, practically, all their 

 work with these kilns. 



The points in regard to the kiln are as follows : 



1. Cost. A kiln which will hold six thousand gallons of pans or closely 

 nested ware, or three thousand gallons of ware as it comes from the shop, 



