Newly developed methods and calibrations for determining the age of fl
aked obsidian surfaces have been described and applied to New Zealand
archaeological obsidians. Hydration bands were measured under high mag
nification (1000 x) using a MOCHA imaging system to an accuracy of 0.2
mu m. Hydration rates were calculated on the basis of obsidian water
content as estimated from artefact density while effective hydration t
emperatures were established from published temperatures derived from
thermal cells. Hydration dates have been compared with radiocarbon dat
es from six archaeological sites in the North Island of New Zealand. T
he obsidian age determinations correlated well with the radiocarbon da
tes from the same context. These results validated the ability of obsi
dian hydration dating procedures to provide accurate calendar year age
estimates. (C) 1996 Academic Press Limited