Ceramic technology: how to recognize clay processing

Abstract

The issue of clay processing concerns both provenance and techno-functional ceramic investigations. In the former, the compositional/textural modification of clay alters the petrofacies expressed by the ceramic body and causes a change from the raw material in terms of bulk chemical and mineralogical composition and petrographical features as well. In the latter, identifying the signs of clay processing will provide information on the steps of the chaine operatoire and on the technological choices made to adjust paste plasticity and to avoid failures in the following stages of manufacture. Several examples of clay processing were considered, encompassing deliberate addition of natural and artificial temper and clay mixing, other than fractioning and homogenisation to prepare the forming stage. The expected effects of mineral, vegetal and animal tempers on the paste and on the fired body were outlined. Finally, some analytical guidelines are provided to identify clay processing, using the most common analytical methods. Optical microscopy and electron microscopy provide the main contribution to identifying most of the processing practices on the clay, whereas bulk methods provide indirect evidence that may alone be insufficient to prove the occurrence of a specific transformation, as well as to detect homogenisation features. However, only a careful and multidisciplinary investigation of the ceramic body will help reveal the actions of the chaine operatoire and to test archaeological models in a sound bottom-up perspective.