THE MANUFACTURE OF CLAY PRODUCTS. 215 



the clay miner, and often mean no more than that the clay is the 

 best or second best dug by him. 



Stonezvare clayd. — Under this term are included such clays as 

 are adapted to the manufacture of stoneware. They must, there- 

 fore, possess good plasticity, dense-burning qualities and prefer- 

 ably good tensile strength. The lower grades of stoneware are 

 often made from a nonrefractory clay, but the better grades, and 

 in New Jersey even the common ones, are generally made from 

 a No. 2 fire clay. 



Sagger clay. — This is a term applied to clays which are used 

 in a mixture for making the saggers, in which the white ware and 

 other high grades of pottery are burned. They are commonly 

 rather siliceous in their character, although some may be used on 

 account of their bonding power and freedom from, grit to hold 

 the more porous grades together. As far as the physical prop- 

 erties go, the sagger clays are not, therefore, represented by any 

 one type. Their refractoriness varies from that of a refractory 

 to a semirefractory clay. 



Wad clay. — This is a low grade of fire clay, which is used for 

 grouting the joints between the saggers, when they are set up in 

 bungs in the kilns. It is dug at several localities in Middlesex 

 and Mercer counties. 



Terra^cotta clay. — This term does not mean very much and is 

 used rather indiscriminately to indicate different beds of clays, 

 which are being dug for the manufacture of terra cotta. In the 

 majority of cases they are semirefractory clays of buff-burning 

 character, sometimes sandy, at other times dense-burning. At 

 one or two places a red-burning clay is dug for 1 terra-cotta 

 manufacture. The wide difference in character between two 

 of them is shown elsewhere in this report. 



Retort clay. — A dense-burning, plastic, semirefractory clay, 

 used chiefly in the manufacture of stoneware. In New Jersey 

 the term is restricted to the Woodbridge district. 



Pipe clay. — This is a term applied to almost any fine-grained 

 plastic clay. Strictly speaking, it would refer to a clay used for 

 making sewer pipe. 



Brick clay. — This includes all impure, nonrefractory clays suit- 

 able for the manufacture of common brick. 



