AFS clay is the percentage of particles with a diameter less than 20 microns in a foundry sand sample. This includes active clay, dead clay, silt and inert fines. The sand sample to be tested must be prepared in the Rapid Sand Washer, Model No. 42119. The AFS Clay Tester stirs a water and sand mixture into suspension and drains the overlaying liquid after a preset settling time. The time between cycles allows only particles larger than 20 microns to settle. If this process is repeated enough, all particles smaller than 20 microns will be removed. A command panel with a keyboard and a liquid crystal display (LCD) operates the tester. An on-board microprocessor can be programmed by the operator via the LCD for several advanced options, including number of cycles and type of sand to be tested. The AFS clay tester can also adjust settling times to compensate for temperature changes. A thermistor registers the water temperature during each settling period. This data is received by the microprocessor which uses this information to correct the settling time for the next wash. The AFS Clay Tester is shipped with a pressure regulator, connecting hoses and 1000 milliliter beaker. The AFS Clay Tester also requires a Rapid Sand Washer, Model No. 42119 to pre-treat the sand sample prior to testing