92 GEOLOGY OF OHIO. 



Stoneware has until comparatively recently been confined to such 

 uses as have been indicated, for containing fluids, and semi-solid materials 

 but a promising trade is now growing up in the manufacture of a special 

 kind of stoneware for cooking purposes, which can be used directly on a 

 fire or stove with safety and great convenience. 



In geographical distribution the stoneware business occupies the 

 same general limits that it did ten years ago. The largest district is at, 

 and near to, Akron in Summit county. The Zanesville district has made 

 great progress and now makes a good second to Akron. Besides these 

 two well defined districts, there are quite a number of large and well- 

 appointed shops in various out-lying points. The Rock House district 

 of Hocking county has ceased to play any part in the business as a 

 commercial factor. 



The clays used in the manufacture of stoneware are confined to one 

 well defined class, and no great variations are detected in analyses from 

 a number of points in the state. 



The qualities which a clay must have to fill the various needs of a 

 stoneware potter are essentially as follows : 



1st. It must be plastic, so that it can be spun and moulded into any 

 desired shape, without the expenditure of any excessive power in pre- 

 paration or the use of excessive strength in turning. There is a great dif- 

 ference in clays in this respect which in others meet equally well the 

 demands of the business. 



2d. It must be refractory enough to stand up well and keep its shape 

 at a heat sufficient to melt the clays which are used for glazes, or to take a 

 good salt glaze on its surface. This condition is of the utmost impor- 

 tance ; a fusible clay will cause the manufacturer a regular percentage of 

 loss in every kiln, which can be avoided entirely by using a stronger clay. 



3rd. While keeping its shape at this heat, it ought to be undergo- 

 ing a process of vitrification which, while not being sufficiently marked 

 to make the ware brittle or glassy, still makes the body practically imper- 

 vious to water. Much stoneware is now made which does not fill this 

 condition, as it is not vitrified at all and depends upon its glaze to make 

 it impervious. 



4th. When burnt with a continuously clear fire or oxydizing 

 atmosphere, it ought to present a clear and uniform tint, varying from 

 light straw yellow or buff when rather soft burnt, to a clear stone gray or 

 blue color when hard. If the clay shows, on short exposure to a smoky 

 flame, a brown tint or scum, it will be undesirable, as it is always likely 

 and almost sure to be exposed to reducing influences in a 40 hours' burn, 

 and a brown color is unpopular in the market. 



5th. Blotches, pimples, blisters or any other eruption on the surface 

 of the ware, which are due to impurities in the clay and not to faults of 

 burning, will rule the clay out, no matter if all other qualities are correct. 



It may seem that it would be a difficult matter to secure clays in 

 which these various qualities are united, but such is not the case. The 



