POTTERY OR STONEWARE CLAYS. 179 



(No. 23 S.) 

 STONEWARE CLAY. 



HEZEKIAH WIGGINS, PAYETTE CO. 



A light gray, hard, compact clay, of moderately silic- 

 ious character and containing a few scattered mica scales. 

 It slakes very slowly to tough scaly flakes. 



In order to make a workable pasie the clay required 

 the addition of 34.3 per cent, of water. This paste was 

 markedly plastic. Its shrinkage in drying was 14 per 

 cent, and 8 per cent, in burning, giving a total shrink- 

 age of 22 per cent. The tenacity of the air dried mass 

 was on the agerage 232 lbs. per square inch with a 

 maximum of 300 lbs. per square inch; which is exceeded 

 by comparatively few clays. ' 



Incipient fusion occurs at 1900° F., vitrification at 2100'* 

 F., and viscosity at 2300° F. The clay burns to a dense 

 red body, but requires slow drying and heating to avoid 

 cracking. 



The composition of this clay is as follows: 



Analysis of Stoneware Olay, H. Wiggins, I'ayette Co. (No. 23 S.) 



Silica (total) 83.27 



Alumina 19.68 



Water 6.05 



Ferric oxide 3.52 



Lime 1.30 



Magnesia tr. 



Alkalies 1.20 



Moisture 3.75 



68.77 



Free silica (sand) 39.59 



Total fluxes 6.02 



Specific grarltj 3.33 



The clay agrees in composition in a general way with 

 some of the stoneware clays of Missouri and Ohio, and 

 its shrinkage and tensile strength are similiar to a ston 



