Viscous remanent magnetization authentication method for archaeological artifacts

Museums and public collections often contain archaeological clay artifacts of unknown origin. Such artifacts, if proven to be authentic, may contribute significantly to our understanding of ancient societies. However, the authenticity of these artifacts is usually highly debated, resulting in their being disregarded in historical interpretations. Several laboratory methods have been developed in order to authenticate such objects but none have been proven infallible. Here we present a method for distinguishing between authentic and fake clay artifacts by considering the Viscous Remanent Magnetization (VRM) acquired by the artifacts. Clay objects tend to acquire a strong magnetic signal termed Thermal Remanent Magnetization (TRM) upon heating and cooling in kilns during their manufacturing process. After being removed from the orientation in which their TRM was acquired, these objects were exposed to an ambient geomagnetic field in a different direction. Over archaeological time scales, this results in the acquisition of a significant VRM. We propose a laboratory protocol for identifying this ancient VRM. We validated the protocol using micromagnetic modeling of single domain particles and by laboratory experiments carried out on 19 ancient and 26 modern objects, made from different types of clay and fired using different firing techniques. Both the experiments and the simulations indicate that the existence of a significant VRM component removed at temperatures higher than a cutoff temperature of 112 ° C is indicative of ancient objects while its removal at lower temperatures is indicative of modern objects. We successfully applied this method to objects of debated authenticity.