Obsidian hydration dating definition


20-Dec-2014 17:02

When this hydrated layer or rind reaches a thickness of about 0.5 microns, it becomes recognizable as a birefringent rim when observed as a thin section under a microscope.

Hydration rims formed on artifacts can vary in width from less than one micron for items from the early historic period to nearly 30 microns for early sites in Africa (Michels et al. Formation of the hydration rim is affected not only by time but also by several other variables.

Once a hydration layer has been measured, it can be used to determine the relative ages of items or, in some circumstances, can be converted into an estimated absolute age.

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).

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The most important of these are chemical composition and temperature, although water vapor pressure and soil alkalinity may also play a role in some contexts.

The effects of these variables have often been summarized and will not be discussed further here (Michels and Tsong 1980; Friedman and Obradovich 1981; Freter 1993; Hull 2001; Stevenson et al., 1993, 1998, 2000; Friedman et al. 1999, Ridings 1996; see Skinner and Tremaine 1993 for additional references).

These cuts produce a cross-section of the artifact approximately one millimeter thick which is removed from the artifact and mounted on a petrographic microscope slide with Lakeside thermoplastic cement. A New Dating Method Using Obsidian: Part I, The Development of the Method.

The mounted specimen slide is ground in a slurry of 600 grade optical-quality corundum abrasive on a plate glass lap.

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.

The potential of the method in archaeological chronologic studies was quickly recognized and research concerning the effect of different variables on the rate of hydration has continued to the present day by Friedman and others. In Chronometric Dating in Archaeology, edited by R.