The rheology of clay may be divided into three almost distinct fields; thestudy of liquid “slips,” i.e., the relatively dilute liquidsuspensions used for casting, mainly in the manufacture of pottery, or ofplastic bodies, mouldable but capable of retaining their moulded shape undertheir own weight, or of the deformation of the fired material at hightemperatures. Consideration of time available made it necessary to restrictthe present considerations to the second of these, the plastic state.