Based on the Pfefferkorn Theory, this device measures the deformation of a plastic clay specimen under the fall of a metal plate. The results are normally expressed as graphs showing height reduction as a function of moisture content. Carrying out the test requires considerable preparation, record keeping and the ability to effictively measure water content. Interestingly, upon compilation of the data for a given clay body (which is trusted to be of consistent plasticity), the results of this test can approximate the water content. This tester can be useful with glazes also, since they employ clay (which most do) they have plasticities (that is what hardens them on drying and suspends them in a slurry). The degree of plasticity walk a line between enough to deliver needed dry hardness but not too much to produce drying cracks.
Pfefferkorn Plasticity Tester at CeramicTestingEquipment
Plasticity (in ceramics) is a property exhibited by soft clay. Force exerted effects a change in shape and the clay exhibits no tendency to return to the old shape. Elasticity is the opposite.