Fresh surfaces of obsidians are hydrated in the laboratory and the thicknesses of the hydrated layers are determined by hydrogen depth-profiling using secondary ion mass spectrometry and ₁₉F nuclear reaction. It appears feasible to establish a hydration equation which will allow obsidian artifacts to be independently dated by their hydrated depths. However, it is important to operate in hydration time and temperature regimes in which dissolution of the obsidian surface can be avoided. -- AATA