Sourcing Shell and Shell-Tempered Artifacts Using Laser Ablation (2009-02)

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Summary

Shell samples

This project involved developing a new method for using the chemical content of freshwater mussel shell as a means of sourcing prehistoric, shell-tempered pottery and shell artifacts to their places of origin.  By extension, this means that prehistoric trade and exchange networks can be mapped out.

The method is based upon the fact that freshwater mussels take up chemicals from the waterways they inhabit.  Because each waterway is chemically different to some extent, and because mussels incorporate the chemicals into their shells, it is theoretically possible to identify where shell artifacts or shell-tempered pottery was made by chemically analyzing the shell.

Analysis of shell samples

It was proposed to do this using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry, a non-destructive method that uses a laser beam to remove a very small amount of material for chemical analysis.  The non-destructive nature of the method means that it can be applied to sensitive artifacts such as burial accompaniments or museum specimens.

The first step in developing this method was to begin construction of a freshwater shell chemical database against which the chemical content of shell artifacts could be compared.  Because of modern pollutants, archaeological shells representing food waste were obtained from a number of sites and chemically analyzed via LA-ICP-MS.

The results show that shells from different waterways form distinct chemical groups, validating the theory and providing the first set of background data for applying the method at a regional scale.

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