Obsidian contains water trapped in it during its formation.
In its natural state, it has a thick rind formed by the diffusion of the water into the atmosphere when it first cooled--the technical term is "hydrated layer".
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Such variability exists within any given obsidian source, and even within any particular specimen.The synthesis of this body of hydration-dating research may help archaeologists more constructively decide how and when to apply this unique and versatile dating technique to their specific research questions by providing the information and guidelines necessary for recovering pertinent field data.INTRODUCTION | PREPARATION METHODS | REFERENCES The obsidian hydration dating method was introduced to the archaeological community in 1960 by Irving Friedman and Robert Smith of the U. When a new surface of obsidian is exposed to the atmosphere, such as during the manufacture of glass tools, water begins to slowly diffuse from the surface into the interior of the specimen. In order to transform the hydration rim value to a calendar age, the rate of the diffusion of water into the glass must be determined or estimated. The hydration rate is typically established empirically through the calibration of measured samples recovered in association with materials whose cultural age is known or whose age can be radiometrically determined, usually through radiocarbon dating methods (Meighan 1976).