Pinson Mounds pottery study

NAA study of approximately 170 sherds from the site was undertaken to answer this question. This totally included 117 sherds and three fired clay samples from Pinson Mounds, 39 sherds from nearby contemporary sites, five samples of clay sources in the area, and six sherds from a Hopewell site in Georgia. Nineteen of the sherds from Pinson appeared to be nonlocal in style and temper. The research reactor at the University of Missouri was used to irradiate the samples and instruments measured the abundance of 33 elements in ppm in the pottery. Statistical analysis of the data from the NAA study was then undertaken. The authors of this study, Mainfort and colleagues, removed a number of samples with unusually high or low data values (known as outliers) from their study, arguing that these outliers can cause samples to appear more similar. 

A scatterplot of the results, with outliers, removed, showed three groups of pottery based on their elemental composition (Fig. 8.13). The values used on the X- and T-axes of the scatterplot are based on principle components, a technique to create summary statistics that combine the results from all of the elements used in the study. Each data point on the graph represents a sherd sample from Pinson Mounds. Thus, the X- and T-axes use most of the results of the NAA measurements. The authors of the study then drew ovals around clusters of data points in the graph to distinguish three compositional groups. These ovals should encompass 90% of the data points in the group. These compositional groups should represent pottery... 

The authors of the study did not so much attempt to determine the composition of exotic pottery from different places for comparison in their study, but rather relied on the provenience postulate. The provenience postulate states that chemical differences within a single source of material must be less than the differences between two or more sources of the material, if they are to be distinguished. Thus, Mainfort and colleagues in this study argue that chemical differences within the pottery from Pinson Mounds are large, and thus all of the pottery studied in then-sample was produced locally. They found no chemical evidence for the long-distance importation of pottery. 

A few years after the NAA study, Mainfort worked with James Stoltman using another technique to reexamine the question of pottery import at Pinson Mounds. Stoltman used ceramic petrography to study the physical composition of the sherds. Ceramic petrography involves the identification of minerals in the temper of the pottery and the measurement of the matrix of the sherd in terms of particle size. The percentages of silt-size inclusions plus the type, size, and percentage of mineral inclusions of sand size and larger were determined to characterize each sherd. This is very different information from the chemical composition recorded in NAA studies. The two approaches characterize ceramic compositions in distinctly different ways -one in terms of chemical elements, the other in terms of minerals and rocks - and are generally believed to provide complementary information. 

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