The dating technique called obsidian hydration analysis is a favorite of archaeologists, both because it is relatively secure and because it is relatively inexpensive.
The technique relies on the fact that a measurable rind grows at a known rate on the surface of the lithic material called obsidian when it is freshly exposed, such as by a break or purposeful flaking.
Obsidian hydration as a dating method isn't perfect, because it takes several centuries to build up a measurable rind and the rind has a tendency to crumble. Rind growth is also a function of temperature, water vapor, and variable obsidian chemistry, which are limiting factors to the usefulness of the technique.
Eerkens, Jelmer W., et al. 2008 Obsidian hydration dating on the South Coast of Peru. Journal of Archaeological Science 35(8):2231-2239.
Jones, M., P. J. Sheppard, and D. G. Sutton 1997 Soil temperature and obsidian hydration dating: A clarification of variables affecting accuracy. Journal of Archaeological Science 24:505-516.
Ridings, Rosanna 1996 Where in the world does obsidian hydration dating work? American Antiquity 61(1):136-148.
Rogers, Alexander K. 2008 Obsidian hydration dating: accuracy and resolution limitations imposed by intrinsic water variability. Journal of Archaeological Science 35(7):2009-2016.
Stevenson, Christopher M., Ihab Abdelrehim, and Steven W. Novak 2004 High Precision Measurement of Obsidian Hydration Layers on Artifacts from the Hopewell Site Using Secondary Ion Mass Spectrometry. American Antiquity 69(3):555-568.
Webster, David, AnnCorinne Freter, and David Rue 1993 The obsidian hydration dating project at Copan: A regional approach and why it works. Latin American Antiquity 4(4):303-324.
This glossary entry is part of the Dictionary of Archaeology.