Insights on the firing temperature of ancient ceramic coffins through a multi-analytical approach: The case of the Sada Nishizuka Kofun, Japan

Investigating the heating temperatures of ancient ceramic artifacts can offer information about their production technology and enrich our knowledge about the fire control skills in ancient times. We present here the results of a multi-analytical approach, including magnetic, X-Ray Powder Diffraction (XRPD) and thermoluminescence (TL) analyses, applied on the investigation of the equivalent firing temperature of the ceramic coffin (No 2) found in the well-known Sada Nishizuka Kofun, Japan. Monitoring of the magnetic properties of the studied fragments versus laboratory heating showed clear magnetic enhancement at relatively low temperatures around 350-500 degrees C. The magnetic results were compared with independent data obtained from XRPD and TL analyses. The XRPD patterns showed the presence of quartz, plagioclases and clay minerals such as muscovite and smectite, which indicate firing temperatures lower than 850-950 degrees C. The presence of kaolinite in almost all the studied samples lower the estimate temperature below 550 degrees C. Such data were further confirmed by the TL analysis which suggest firing temperature lower than 525 degrees C. The results obtained indicate that the coffin was most probably produced in an open or covered kiln, following the Japanese Haji-type traditional production, reaching maximum firing temperature lower than 550 degrees C. This study offers the first archaeometric experimental data to better understand the production strategy of ceramic coffins during the Kofun period in Japan and highlights the potential of non-conventional archaeometric analyses, such as magnetic and thermoluminescence investigations, to obtain information on firing procedures for ancient ceramic artifacts.