Determination of clay plasticity: Indentation method versus Pfefferkorn method

As a basis of ceramic process development, raw material selection plays a fundamental role in the final product design. For correct material selection, knowledge regarding all the properties of the raw materials should be obtained. Plasticity is one of the most important properties for molding clay products. Nevertheless, the standard methods in use, including the Pfefferkorn method, are not precise and reliable. They are based on subjective qualitative information and are dependent on technical skills. The literature shows some attempts to improve the test method, all based on the force needed to indent a clay sample surface with specific water content. Four different clays were studied and the plasticity values due to the Pfefferkorn method and the indentation test were compared. The results showed that the indentation method is reliable and more precise compared to Pfefferkorn. It is also faster and more practical.