124 GEOLOGY OF OHIO. 



watchfulness and skill which accompany the production of any clay ware 

 that owes its value to its vitrification. 



The method of preparation of the body for these various kinds of 

 ware is substantially alike. The ingredients are collected in a charging 

 car or box, each one being carefully weighed.. They are shoved into, the 

 blunger and united in the most intimate mixture by the formation of a 

 fluid slip. The screens employed are brass or silk gauze from 100 to. 160 

 mesh to the inch. The strained slip is run through a magnet, box in 

 some potteries to try to separate out any magnetic particles of iron from 

 the machinery or clays. 



The pressing and pugging offer no peculiarities. 



The pottery processes are also much the same as described before, 

 except that as the wares grow more costly, the value of the machinery 

 and appliances increases in like proportion. 



The use of every mechanical contrivance which can assist them is 

 freely adopted by potters of this grade. 



The burning is accomplished in just the same way as in yellow ware, 

 except that the saggers are made of better material and are glazed inside 

 to prevent the ware from becoming soiled by any effloresence from the 

 sides of the saggers. 



The heats required vary of course with the kind of body com- 

 pounded. The best practice in making the white granite body is to 

 make a rather refractory body which requires a high heat to bring it to 

 its proper degree of combination. When such a body is given the proper 

 heat, it is stronger and tougher than one which matures at a lower tem- 

 perature, and consequently the weight of clay used for each piece may 

 be decreased a little, and the ware becomes lighter and more delicate 

 without loss of strength. 



The heats employed in burning white granite and CC ware were 

 tested in one factory of each kind with the following results: 



But there is no probability that these temperatures stand for these 

 respective classes, as the body is bound to vary in its chemical qualities 

 according to the composition which the potters give it and in this they 

 are regulated each by his own preference. The limits of variation in 

 which a good body may be produced are rather large. 



The glazes used in the white ware potteries are much more complex 

 than the yellow ware glazes. The nicest problem the potter has to 

 handle, is the adjustment of his glaze to his body. The defects of the 



