A proxy of potters’ throwing skill: ceramic vessels considered in terms of mechanical stress

This study is aimed at evaluating potters’ skills according to the mechanical characteristics of the vessels they produced. It focuses on wheel thrown vessels. In a first stage, considering that the difficulty of throwing ceramic vessels is to a significant extent determined by the risk of collapse of the thrown structure, we applied the method of finite element modelling to derive an index of mechanical stresses operating within a vessel. Validated via compression tests, the so-called Von Mises stress index was employed as a global index of mechanical difficulty. Because this index allows comparisons between vessels of different form, mass, and clay properties, it provides a more powerful tool than existing techno-morphological taxonomies. In a second stage, in order to relate the Von Mises stress index to throwing difficulty, we analysed the geometrical and mechanical characteristics of vessels thrown by eleven expert potters invited to reproduce four different model forms with two different masses of clay. The results demonstrated that reproductions revealed subtle but systematic deviations from the model forms that allowed a decrease in the mechanical difficulty. More difficult forms showed larger degrees of mechanical optimisation. These results, in combination with a new analysis of data from Roux’s (1990) study with potters of different skill levels, indicate that skill resides, at least to a certain extent, in the capacity to marshal the operative mechanical constraints. In other words, the latter, measured by the Von Mises index, provides a useful signature of a potter’s skills.

Research highlights
► Expert potters threw vessels of different form and mass.
► Finite element modelling of vessels allowed calculation of mechanical stresses.
► The Von Mises stress index captures the difficulty of throwing different vessels.
► Geometrical deformations observed in thrown forms reveal mechanical optimisation.
► Skill can be inferred from mechanical analysis of ancient thrown vessels.