Rehydroxylation (RHX) dating: Issues due to short term elevated temperature events

Abstract

The long-term uptake of environmental moisture (rehydroxylation) is a property of fired clay ceramics. Rehydroxylation dating (RHX) attempts to provide age estimates for ceramics by measuring the associated mass gain and evaluating the duration over which this gain occurred. Simulations of the potential additional mass gained by fired clay ceramic brick and pottery due to short term (minutes to days) elevated temperature (>50°C) events, STETEs, and the effect this has on age estimations as part of rehydroxylation dating trials were explored. These events, including post-firing cooling of a brick, the use of pottery in cooking, and heating/cooling cycles during drying, for example, add considerable quantities of (re)hydroxyl mass to the sample and, particularly for samples with high activation energies (>130kJ/mol), the effect on age estimations can in some instances be detrimental (of the order of hundreds or thousands of years); where the activation energy is lower, the effects only become considerable at higher temperatures (e.g. >75°C) and over longer durations (days). Simulations of the STETEs for a brick cooling over a range of activation energies and for a variety of post-firing cooling durations and cooling temperature profiles, as well as for a pot undergoing varied numbers of cooking cycles (stewing and boiling) are presented, highlighting the magnitude of the issue if unaccounted for. STETEs are also shown to be a plausible major contributor to the age discrepancies (resulting in very old ages) between known and estimated ages in associated dating trials. The implications for RHX dating are discussed.