Temper and temperament of prehistoric craft: Temper type evolution and clay body 'workability'

Temper is an additive incorporated into clay during the formation of a ceramic vessel, and may consist of various materials. In a number of previous experiments over the past several decades, archaeologists have experimentally demonstrated that tempers used by prehistoric craftspeople would have imparted important post-firing use-life properties to ceramic vessels. However, although widely touted, the notion that prehistoric temper types would have aided in pre-firing vessel formation has never been systematically tested. Here, we experimentally assess whether calcium carbonate-based tempers, like limestone and burnt shell, would have made clay bodies more workable relative to silicate-based grit temper, as has been previously proposed. In this study, participants were asked to build five simple and challenging three-dimensional forms using grit-, limestone- and shell-tempered clay bodies, and then rank these conditions in terms of workability. Our statistical and qualitative assessments of these data were unambiguous: contrary to claims in the scientific literature, the calcium carbonate tempers did not make clay bodies more workable, and were consistently, sometimes significantly, ranked lower than silicate grit-tempered clay bodies in terms of workability. Our results have several implications for temper selection and evolution in prehistory, specifically during the widespread silicate grit to calcium carbonate transition during the Late Woodland period (AD 500‐1400) of the North American Midwest.