COMPARISON OF WEAK ACID EXTRACTION CHEMISTRY AND ELECTRON MICROPROBE ANALYSIS OF PASTE COMPOSITIONS FROM A SUITE OF COLONOWARE POTTERY, BROOM HALL PLANTATION, CHARLESTON, SOUTH CAROLINA

Archaeological ceramics are an important guide to the culture, technology, and development of a civilization. Commonly, analytical techniques similar to those used in geologic studies are applied by the archaeologist to identify the paste (mainly clay minerals) and the temper (aplastic) components of the pottery. Although petrographic techniques can easily identify the larger temper components, the identity of the fine-grained clay minerals of the paste is obscured by the vitrification that occurs during the firing process. Two chemical methods often used to evaluate the paste components are the weak acid extraction method (Burton and Simon, 1993) and the electron microprobe. The weak acid extraction method is thought to selectively dissolve the paste component with no (or minimal) interaction with the larger temper component(s). However, little study has been done to check what really is being dissolved during this process and the validity of the hypothesis. This study compares the results of the weak acid dissolution technique with electron microprobe analyses for two forms of Colonoware (Yaughan and River Burnished) recovered from the Broom Hall Plantation, South Carolina (Trinkley et al., 1995). Microprobe and petrography sections were taken from the samples prior to the weak acid extraction treatment. ICP analyses (XRAL Laboratories) reported 21 elements which were compared to electron microprobe analyses taken at15 kV, 5 nA, and varied spot size. The paste appeared to be made up of very small (<1 µm) areas of slightly differing grayscale in back-scatter electron imaging (BSI; indicating different compositions), which were impossible to analyze separately. Care was taken to avoid discrete, aplastic (>10 µm) particles (quartz, etc) during the microprobe analysis. Results of this study show little correlation between the weak acid extraction data and the microprobe results. These results have important implications for the viability of the weak acid extraction method for the analysis of archaeological samples.