Obsidian Hydration Dating: Summary and Status of a Physics-Based Approach

Abstract

ABSTRACT Obsidian hydration dating (OHD) is a method of computing archaeological ages based on measuring water absorption by obsidian artifacts, and is widely used in the western United States. This abstract provides a single resource for the OHD user, including advances over the past decade. We describe obsidian mineralogy as it affects OHD; the effects of structural water content on hydration; the mathematical form of the hydration law; methods to control for structural water content and temperature history; methods for computing hydration rates; an analysis of error sources; and a method for conducting an OHD analysis. We address OHD as currently practiced in the western United States, based on optical microscopy, and do not describe newer, experimental methods such as Secondary Ion Mass Spectrometry or infrared (IR) spectroscopy. An associated OHD workbook in MS Excel is available on the website of the International Association for Obsidian Studies.