Ceramic rehydroxylation dating by infrared diffuse reflectance spectroscopy

Abstract

We provide a new approach to the method of ceramic dating by tracking the dehydroxylation and rehydroxylation of water species using infrared diffuse reflectance spectroscopy. Water bands at 3655 cm⁻¹ (OH/H₂O), 4550 cm⁻¹ (OH), and 5160 cm⁻¹(H₂O) were used to determine the various forms of water absorbed or released from the ceramic surface and the interior, which permitted the calculation of prehistoric hydroxyl gain since the time of manufacture. Ramped temperature rehydroxylation experiments (30–500 °C) were used to establish the activation energy (E) of OH diffusion. This was followed by an isothermal diffusion experiment, which provided a high temperature (240 °C) diffusion coefficient that was extrapolated to archaeological temperature. This new variant of the dating method is an alternative to the conventional mass gain experiments that have been applied in the past. Our ceramic dates are in agreement with associated radiocarbon dates within shell midden deposits created by the 17th century Native Americans on St. Catherines Island, Georgia, USA.