Salt production in pre-Funan Vietnam: archaeomagnetic reorientation of briquetage fragments

Bronze to Iron Age briquetage found in the northern Mekong Delta has an appearance similar to analogous material from Europe and Asia; however, the orientation in which the briquetage was employed during the production of salt is still under debate. As a consequence of the heating and subsequent cooling of the briquetage during the evaporative recovery of salt, the magnetic mineral particles within the ceramic formed a stable thermoremanent magnetization in alignment with the Earth's magnetic field. It thus becomes possible to find the orientation in which the ceramics were last fired by aligning their recorded archaeomagnetic signal with estimates of the Earth's ancient field direction in Vietnam. The archaeomagnetic directions obtained from 22 samples taken from five different briquetage artefacts are somewhat scattered, but they reveal a consistent orientation and thus the mode in which the briquetage was employed can be reconstructed.