232 new york state museum 



Stoneware 



The following description of tlie manufacture of stoneware 

 and earthenware is quoted from vol. Y of the Geological survey 

 of Ohio. 



" Stoneware is the product of an unmixed, natural clay, burnt 

 at high enough heat to oblige the impurities to combine with the 

 dry silica and thus cause an incipient vitrification or fretting 

 without loss of shape. It should be impermeable to water with- 

 out any glazing on it, but it frequently fails in this point. The 

 color is bluish gray due to combined iron." 



" Earthenware is a product of very similar clays burnt a little 

 to vitrify the body or combine the iron. It is of a yellow or red 

 color from the free iron and is porous unless glazed." 



The successive steps in the manufacture of stoneware are 



1. Wetting the clay. 



2. Grinding. 



3. "Wedging. 



4. Turning. 



5. Drying. 



6. Slipping. 



7. Burning. 



8. Sorting the pro luct. 



The wetting or soaking of the clay is usually done at small 

 works where the grinding machines are operated by horse 

 power. Several kinds of grinders are used for the clay, the 

 simplest one being the pug mill. A machine often used at many 

 potteries consists " of a square frame pivoted on an upright beam 

 which runs through the point of crossing of the diagonals. 

 On the projecting ends of this frame are fastened cart wheels 

 which work in a circular trough beneath. The whole frame 

 revolves by the motion of a large cog wheel above, which receives 

 its power from the horse or engine. The machine is slowed up by ' 

 weighting the corners of the frame. The wheels in their revolu- 

 tions manage to cut the clay to pieces quite effectually." This 

 machine has a capacity for grinding from 1,200 to 1,500 pounds 



