THE PRODUCTS OF CLAY AND FIRE 



performed by the pug-mill. This machine resembles 

 a large sausage-machine in its mechanism, having a 

 horizontal, cylindrical body in which the blades re- 

 volve about a shaft running through the center. The 

 clay is fed in at one end of the cylinder, where it is cut, 

 kneaded, and pressed along the body of the machine, 

 and finally is squeezed through an opening at the oppo- 

 site end, more thoroughly " wedged" than is possible 

 by hand. As it emerges from the pug-mill it is cut 

 off in sizes convenient for handling, by means of a brass 

 wire, and is then ready for the workmen. 



THE GLAZE AND ITS PREPARATION 



There are many intermediate steps in the manu- 

 facture of pottery between the "wedging" and the final 

 application of the glaze, but as many processes in the 

 preparation of the glaze closely resemble those used in 

 preparing the clay, it will perhaps be as well to consider 

 them here. 



When the peculiar qualities of a perfect glaze are con- 

 sidered, it is not surprising that it took so many centu- 

 ries for potters to discover and perfect it. The coating 

 of glaze when applied to ware in the biscuit state plays 

 the same part that a coat of paint does to a wooden 

 building it adds beauty and gives permanence to the 

 structure. But the comparison ends here. When 

 fired, the glaze becomes a part of the ware it covers, 

 not a superficial layer, as in the case of paint applied 

 to boards. It must be sufficiently hard to resist abra- 

 sions, not affected to any extent by acids, must fuse at 



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