THE PRODUCTS OF CLAY AND FIRE 



made. From such mixtures the impurities are re- 

 moved more readily than would be possible from the 

 clay in the natural state. The exact amount of solid 

 substance per pound can also be determined more 

 readily and more accurately than in the more solid 

 forms. For these reasons many pottery establishments 

 mix all their ingredients in water, the mixtures being 

 known technically as "slips." The exact amount of 

 solid material contained in each slip is known, and 

 may be easily measured in the simplest manner. 

 For example, a pint of ball-clay slip that weighs 

 twenty-four ounces will contain approximately six and 

 one-half ounces of dry material. If this is the propor- 

 tion desired the workmen can easily obtain the neces- 

 sary mixture by adding water to the clay which is 

 stirred, or "blunged," so as to be of uniform density, 

 until his pint measure when full tips the scales at the 

 twenty-four ounce mark. 



Of course it is possible to reduce all the materials 

 to a perfectly dry state, mix them in the desired pro- 

 portions, and bring them to a workable plastic state 

 by the addition of water; and this method is used in 

 some of the large factories. The usual method, how- 

 ever, is to make slips of the different materials, each 

 slip of predetermined strength, mix them all together, 

 and then remove the excess of water. 



China-clay, the other substance coming in the first 

 class of materials, is a white, earthy substance, easily 

 pulverized. In this country it is very generally called 

 kaolin. Like the blue clay it is found in many differ- 

 ent countries, China and Japan, Germany, France, 



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