Roman double-layered crucibles from Autun/France: a petrological and geochemical approach

Eighteen double-layered crucible fragments found in an archaeological excavation site of the Lycee militaire (Autun/France), which dates to the Gallo-Roman period, were analysed with a series of classical mineralogical techniques in order to obtain knowledge about the raw materials of the individual layers. This work focuses on the usage of the crucibles as well as technical aspects of their production. The crucible fragments were studied by using petrographical (optical microscopy), elemental (SEM-EDS, EMPA, XRF-WDS) and mineralogical (XRD) techniques. The two main layers of the crucibles are made of high refractory, kaolinite-based ceramic with granite-related temper grains. The analytical and petrographical results show remarkable differences between these two layers. The outer one is dominated by a high content of vitrified mullite-bearing matrix and contains analcime which was formed during the burial stage. In contrast, the inner layer is characterised by a non-vitrified matrix with a high content of orthorhombic mullite, beta-cristobalite and a-quartz. An engobe is detectable in the majority of the fragments. The mineral composition allows an estimation of the firing temperatures, which have reached approximately 1200 up to 1400 degrees C. (C) 2012 Published by Elsevier Ltd.