n A small BALL MILL utilizing a portable jar of porcelain or metal rather than a fixed cylinder for containing the material to be ground and the grinding media. After being charged and tightly closed, the jar is placed on a pair of rubber rollers – one driven, the other idling – and rotated for the desired time, typically overnight. (Perry's chemical engineer's handbook, 7th edn. Perry RH, Green DW (eds). McGraw-Hill, New York, 1997; Weismantal GF (1981) Paint handbook. McGraw-Hill, New York) Ball Mill.