Ceramic raw materials: how to recognize them and locate the supply basins—mineralogy, petrography

This tutorial paper is focused on the mineralogical-petrographic characterization of clayey raw materials with the purpose of sourcing supply basins and answering questions about the provenance of the corresponding archaeological ceramic artefacts. The first part gives general indications of how to profitably study archaeological ceramic thin sections through the polarizing microscope. Brief notes are provided on the theoretical basis of optical microscopy. A scheme is then provided for the petrographic description of ceramic samples, concerning the textural and compositional characteristics of aplastic inclusions and groundmass. Suggestions are also given for identifying any minero-petrographic marker and establishing minero-petrographic groups (MGP) aimed at archaeological ceramic provenance studies. After broadly describing the geological origin of the clay deposits, there is discussion of how to plan a field survey aimed at the location of clay sources and sampling. The importance of the ethnoarchaeometric approach in provenance studies is also underlined. The third part of the paper describes the preliminary treatments to which the clayey raw materials are subjected before reporting on a grain size analysis and how to proceed when performing experimental firing tests. Finally some suggestions are made about how to compare clay firing tests (experimental briquettes) and archaeological ceramic finds when assessing a production centre.