Infra-red photoacoustic and secondary ion mass spectrometry measurements of obsidian hydration rims

A procedure has been developed for measuring obsidian hydration rim thickne sses on archaeological artefacts using infra-red photoacoustic spectroscopy (IR-PAS). Calibration of the IR-PAS values with depth was completed using secondary ion mass spectrometry (SIMS) and optical microscopy to relate the quantity of diffused water to the measured thickness of the hydration laye r. By monitoring the absorbance intensity at 1630cm(-1) wavenumbers, hydrat ion rims between approximately 1,m and 12,m may be accurately measured and used for chronometric age estimates. SIMS depth profiling has the ability t o measure layers less than 1,m thick, extending the age calibration to samp les of less than 100 years in age. Copyright 2001 Academic Press