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.
It was proposed to do this using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), 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.
This research was made possible through Grant MT-2210-05-NC-05 from the National Center for Preservation Technology and Training (NCPTT).