Storage or cooking pots? Inferring pottery use through archaeomagnetic assessment of palaeotemperatures

In this paper we report the results of an archaeomagnetic and rock-magnetic study performed on a set of Neolithic and Chalcolithic potsherds from El Portalón de Cueva Mayor site (Sierra de Atapuerca, Burgos, Spain) to investigate their thermal history and obtain information about their function during ancient times. Two types of palaeomagnetic behaviour have been observed. One yields stable and univectorial magnetization diagrams (Type 1) while the other yields multivectorial diagrams with an intermedium component interpreted as a partial thermoremanence (p-TRM) (Type 2), acquired during a partial reheating of the pottery during their use. To investigate the connection of these two types with the ancient function of the potsherds, a set of modern pots was experimentally fired and then partially reheated al known temperatures. The results obtained reproduced patterns similar to those observed in the archaeological samples. Type 1 (univectorial) samples that reached only a high heating temperature (>600 °C) during their manufacture were most probably used as storage vessels. By contrast, Type 2 (multivectorial) samples probably recorded a p-TRM acquired during their last use (reheating) related to cooking activities (<450 °C). Additionally, a detailed microprofile performed on an experimental pot heated twice at different temperatures allows interesting inferences to be drawn on the magnetic record in archaeological pottery and its implications. This study shows that the magnetic measurements can be a useful tool to infer the last re-heating temperatures in prehistoric ceramics and to relate them to the use of those pieces in the past.