Evaluation of the rehydroxylation dating method: Insights from a new measurement device

• New multi-sample device for rehydroxylation dating is presented.
• Heating duration of samples at low and high temperatures is a critical parameter.
• Long-term sample mass stabilization not observed even after prolonged drying at 105 °C.

The recently published rehydroxylation (RHX) dating method applicable to baked clay artifacts potentially represents a major tool for research in geoarcheology and archeomagnetism. We report on a new experimental device customized to conduct RHX experiments on series of ten samples without any operator manipulation. We applied the rehydroxylation method on precisely dated French archeological fragments. Our device provides adequate environmental experimental conditions, yet our observations identified several difficulties. First, based on the published protocol, the “archeological mass” of a sample should be determined following an initial drying at 105 °C when the slope of the mass over time is zero. In all our experiments on ∼60 samples, no stabilization of the sample mass is reached even after several weeks of monitoring. This is always true whether the heating at 105 °C was short (a few hours) or long (several days), which may indicate that a slow diffusion process is ongoing even after a low-temperature heating. Second, the initial sample mass following the heating step at 105 °C or 500 °C remained dependent on the duration of heating even though both short and long heating were applied. We demonstrate that the duration of heating at both 105 °C and 500 °C is a critical parameter for the RHX dating method. Further methodological improvements, including the selection of suitable fired clay fragments, are thus required so that the RHX dating method becomes reliable and efficient.