Rehydroxylation (RHX) dating: Mass loss issues due to incomplete drying, carbon content, and mineral alteration

As part of rehydroxylation (RHX) dating trials on post-medieval bricks, investigations were carried out into the presence, and effect on age estimations, of uncertainties associated with (a) prolonged and incomplete drying of samples, (b) the removal of organic and non-organic matter during heating, and (c) mineral alteration during heating. All samples exhibit an issue with a prolonged period of drying, exceeding two months at 130 °C. Methods for treating this issue are applied and demonstrate the need for higher resolution and more precise monitoring of the mass loss during drying if the moisture not removed needs to be taken account of; this may not be necessary if prolonged drying is associated with the slow removal of chemisorbed water, distinct from rehydroxylation-related water loss. Organic matter contamination is also present in significant quantities in all samples, regardless of the retrieval context; the considerable effects of uncertainties in this quantity, arising from variability in the organic matter to organic carbon ratio (OM/OC), on age estimations are presented. Mineral alteration during reheating is generally negligible except when gypsum is present; large sources of uncertainty arising from moisture loss associated with dehydration and with subsequently lower levels of physisorption following reheating are highlighted as problematic.