Weakly Bonded Water in Interstitial Sites: A Source of Inaccuracy in Rehydroxylation Dating

The rehydroxylation (RHX) dating technique offers a promising method for determining the ages of ceramic materials, leveraging the time-dependent mass gain from water reabsorption after high-temperature firing. However, the reliability of RHX dating is under discussion in many cases, with its accuracy depending on the various component materials in ceramics. In the present study, we considered the incomplete removal of weakly bonded water molecules during the conventional preheating step at 105 °C, a phenomenon that may lead to inaccurate mass measurements and overestimates of age. In this study, we propose an enhanced experimental protocol incorporating thermogravimetric analysis (TGA) to identify and quantify interstitial water fractions within ceramics. For samples exhibiting significant water retention (>1%), we recommend preheating at relatively higher temperatures (up to 300 °C) to ensure complete water removal and a more accurate mass determination. This approach was tested on five archaeological samples, yielding improved consistency and agreement with independently known dates. The method highlights the importance of tailored preheating protocols in RHX dating of ancient ceramics.