Rehydroxylation [RHX] dating is a developing method for dating fired-clay ceramics. It is based on the fact that after a ceramic specimen is removed from the kiln at the time of production, it immediately begins to recombine chemically with moisture from the environment. This reaction reincorporates hydroxyl (OH) groups into the ceramic material, and is described as rehydroxylation (RHX). The RHX process produces an increase in specimen weight. This weight increase provides an accurate measure of the extent of rehydroxylation. The dating clock is provided by the experimental finding that the RHX reaction follows a precise kinetic law: the weight gain increases as the fourth root of the time which has elapsed since firing. This so-called power law and the RHX method which follows from it were discovered by scientists from the University of Manchester and the University of Edinburgh.