Dating a medieval pottery workshop of the city of Burgos (Spain): Archaeomagnetic and archaeological evidences

Abstract

Here we report a detailed archaeomagnetic and rock-magnetic study of a pottery kiln from Burgos (Spain) to reconstruct its burning conditions and date its last use and abandonment age. During the course of a rescue archaeological excavation carried out in 2015 in the center of Burgos city, a medieval pottery workshop was discovered. Two well-preserved kilns appeared and archaeomagnetic analyses were performed on one of them. In addition to a large amount of pottery remains, some numismatic and documental evidences provided a general chronological estimation, but the abandonment age of the workshop remains unknown. On the basis of the existing archaeological information we carried out an archaeomagnetic study in order to date its last use. 69 archaeomagnetic samples were collected from the combustion chamber and the kiln's fire tunnel. Stepwise alternating field and thermal demagnetization of the natural remanent magnetization (NRM) were carried out to retrieve the mean direction. Additional experiments consisted in the acquisition of isothermal remanence (IRM), low-field magnetic susceptibility and its anisotropy as well as thermomagnetic curves. Despite the high temperatures expected in the combustion chamber, it appeared that the bricks´ samples from the fire tunnel exhibit the most successful directional results. Magnetite and variable contributions of hematite are the main ferromagnetic minerals observed in the thermomagnetic curves. The type of lithology studied, its previous magnetic history and their location in the kiln strongly condition the observed directional and rock-magnetic results. Additionally, AMS data revealed the manufacturing fabric of the fire tunnel's bricks, showing moderately high anisotropy degrees, but not enough to casts doubts on the directional NRM record. In order to test the reproducibility of the dating results, archaeomagnetic dating was carried out using different geomagnetic field models and the Iberian paleosecular variation curve. The small differences observed in the dating results are mainly due to the density and type of input data of these records. The combination of the archaeomagnetic analyses with the archaeological and documental suggests that last kiln's usage took place during the first half of the XVIth century CE. Overall, this paper illustrates how the combination of archaeological data and archaeomagnetic analyses may improve our understanding about the manufacturing processes, use and age of abandonment of archaeological combustion structures.