Fifty years of obsidian hydration dating in archaeology

About fifty years ago Friedman and Smith [1] recognized the obsidian hydration phenomenon and proposed an empirical dating method based on the conversion of the optically measured hydration depth to an absolute age. They and subsequent researchers developed distinct versions of obsidian hydration method consisting of both empirical rate and intrinsic rate development, thus refining the method. However, in spite the accurately measured rinds beyond digital optical microscopy employing infrared spectroscopy and nuclear analysis, the traditional empirical age equation produce occasionally satisfactory results but still fail to produce a reliable chronometer. In the last ten years, secondary ion mass spectrometry (SIMS) has been employed to accurately define the hydration profile. By modeling the profile of the surface hydrogen concentration versus depth the age determination is reached via equations describing the diffusion process. Finite difference modeling and essential assessments of the novel SIMS-SS (surface saturation) phenomenological method produce a sound basis for the new diffusion age equation and provides promising results. This review refers on the development of obsidian hydration dating (OHD) and diffusion process in glass and reckons future directions of SIMS applications in obsidians.