Modeling Rehydration/Rehydroxylation Mass-Gain Curves from Davenport Ceramics

Rehydroxylation ceramic dating, a new technique that has shown promise as an archeometric breakthrough, was applied to XIX-century samples of Davenport ceramics from Parowan, Utah in the United States. The samples were dried at 500 degrees C to remove both physically and chemically bonded water and then exposed to a 20% relative humidity air to record the progression of rehydration/rehydroxylation over a period of 40d. Both time1/4 and time1/n analyses were applied to the experimental mass gain versus time results in an attempt to find the most appropriate treatment for the data. The time1/4 analysis yielded poor reproducibility and nonideal fitting results to the Stage II mass gain, in which water reacts with meta-clays. Application of the time1/n model, where n is the rehydroxylation exponent, improved the apparent linearity of Stage II mass gain in small samples. However, the time1/n treatment still provided a poor fit to data from larger specimens, indicating that some secondary effects related to sample size and water transport may exist. To examine the effects of porosity and macrostructure on rehydration/rehydroxylation processes, a pulverized sample of the same material was analyzed, resulting in improved sample-to-sample agreement in time1/n irrespective of mass variations. These findings have implications on the application of rehydroxylation ceramic dating.