THE POTTERY INDUSTRY. 295 



of good plasticity, free from grit and burn porous but steel-hard 

 at cone 05-03. 



Clays of this grade are not at all scarce and they occur widely 

 distributed over the State. In the northern counties many of the 

 Pleistocene and post-Pleistocene clays found in the valleys are 

 of the proper quality for flowerpots, and other earthenware vessels. 

 A number of small potteries are supplied from deposits around 

 Linden, near Elizabeth, and some of the red-burning Raritan clays 

 are also adapted to earthenware work. In the central part of the 

 State, the Clay Marl beds I and II are locally sufficiently free 

 from grit to be used, but the Cohansey and Cape May clays are 

 not as a rule sufficiently fusible to burn dense at a low cone. 

 The Alloway clays, however, in the southern part of the State 

 might also be used with success. 



Stoneware clays. — Those commonly employed are semire- 

 fractory clays burning to a nearly impervious body at cones 5 to 

 7, but fusing at about cone 27, although some, dug about Wood- 

 bridge and South Amboy, do' not fuse lower than cone 33 and can 

 be classed as refractory clays. They should possess good plas- 

 ticity, and a tensile strength of not less than 150 pounds per 

 square inch, although many of the New Jersey stoneware clays 

 do not much exceed 100 pounds per square inch. Freedom from 

 soluble salts which will form a scum on the green ware, and 

 freedom from warping and cracking in burning are also essential 

 characters. The clay should not shrink excessively in burning, 

 and should be of a degree of refractoriness to< vitrify at the tem- 

 perature necessary to> melt the glaze. Sulphur in any form is an 

 undesirable ingredient. The better grades of stoneware are com- 

 monly made of a mixture of two or more clays. 



The Raritan beds around South Amboy form, the main source 

 of stoneware clay in the State, and large quantities are shipped 

 from there to potteries in neighboring states. Aside from these, 

 few stoneware clays are found in any of the other formations ex- 

 cept the Alloway clay. Some of the Pleistocene clays may be 

 found suitable for stoneware manufacture, but they would be 

 much less refractory than those of the Raritan formation. None 

 of the Cohansey clays examined, if used alone burn dense enough 



