Thermal profiles in varied experimental firings: Implications for different clays and archaeomagnetism

Thermal profiles of 16 firings performed under various experimental conditions are investigated and compared, with special attention to cooling due to its significance in archaeomagnetism. Samples of different shapes and sizes handmade from six starting clays were fired once and repeatedly followed by magnetic measurements. The collected experimental data provide a broader view of the relationships among firing conditions, clay composition, and final ceramic products. According to direct measurements, open hearths and kilns reach very similar temperatures (800–900°C). Firing temperature and soaking time tend to be linearly related at temperatures around and above 700°C. Soaking time appears to be independent of the structure type around and above 800°C but not below 600°C. Heating rates and times are related exponentially. Only the cooling process distinguishes ’open’ and ’kiln’ firing, with kiln insulation being the primary factor controlling all thermal parameters. A possible relationship between cooling and fuel type is suggested. Cooling in open hearths and kilns differs from that in laboratory furnaces. The magnetic profiles obtained for various clays highlight the differences in composition, grain size, and thermal stability; increasing the number of firings reduces these later.