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Joukowsky Institute for Archaeology



Joukowsky Institute for Archaeology & the Ancient World
Brown University
Box 1837 / 60 George Street
Providence, RI 02912
Telephone: (401) 863-3188
Fax: (401) 863-9423
[email protected]

Obsidian Hydration

Obsidian is a volcanic glass which has seen a multitude of historical applications. It can be easily sharpened into a razor-sharp blade, and its uses have included knives, spears, scrapers, saws, drills, and decorative pieces. Obsidian can be dated due to its water absorption properties. Whenever a piece of obsidian is cut, the process of hydration begins as water absorbs into the surface of the stone. The surface has a particularly strong affinity for water, and will absorb it until saturated. This forms a measurable hydrated layer on the exterior of the obsidian, as the water content increases the density and volume of the space it occupies. The depth of this hydration layer thus indicates the time that has elapsed since the cut was made. The hydration layer is visible under microscopic examination, and measurement of the hydration layer can produce reasonably accurate dating, particularly when completed on numerous samples from the same artifact.


“Dating In Exposed and Surface Contexts”, ed.: Beck, Charlotte. University of New Mexico Press: Albuquerque, NM, 1994.

Michels, Joseph. “Dating Methods in Archaeology”. Seminar Press, New York: NY, 1973.

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Posted at Dec 12/2007 08:01AM:
keffie: I like how you picked an area of interest to you and explored it in greater depth. We didn't address dating methods very comprehensively in class, so you definitely add something valuable with this work!