Determination of the Firing Temperature of Ancient Ceramics by Measurement of Thermal Expansion

Abstract

THE thermal expansion method for determining firing temperatures^1–3 is based on the assumption that, when clays are fired, shrinkage occurs as a result of various sintering processes such as vitrification. Consequently when a clay ceramic is heated up from room temperature (see Fig. 1) it typically exhibits a reversible expansion, characteristic of its mineralogical composition, until temperatures comparable with the original firing temperature are reached. With continued increase in temperature the ceramic begins to contract because superimposed on the reversible expansion there is an irreversible shrinkage associated with resumption of sintering (that is, the firing of the ceramic is being continued beyond the point reached during the original firing). The temperature (T_a) at which a net shrinkage is first observed should therefore provide an indication of the original firing temperature (T_e) of the ceramic.