Ceramic material is very porous so water as vapour readily permeates it.As water molecules chemically combine with the ceramic it gains mass.
This slow progressive chemical recombination of ceramics with environmental moisture due to RHX provides the basis of this archaeological dating technique.
By measuring the rate of mass gain due to RHX and measuring the total mass gained due to RHX since manufacture (obtained by reheating the sample to 500°C), it provides an accurate self-calibrating method of archaeological ceramic dating.
However this long-term uptake of water is both very small and gets progressively slower.
This means that the water demand for RHX is extremely modest.
The RHX dating method, first the mass of the dry sample is measured (green), the sample is then heated to 500°C until all the rehydroxlyated water is removed, this can take several days of heating.