CHARACTERIZATION OF CERAMICS FOUND INSIDE LATE PREHISTORIC POTTER'S WORKSHOP: ANGEL MOUNDS SITE

Structures with a specialized purpose are infrequently identified on archaeologic sites in the Midwestern United States. One structure was identified as Late Prehistoric age possibly used for craft production as a potter's workshop on the Angel Mounds Site, Indiana. Artifacts found inside the structure include ground stone tools and ceramics. The purpose of this study is to physically and chemically characterize the ceramics. Thirty-nine sherds were evaluated; all have plain surface treatment and are shell tempered. X-Ray Fluorescence analyses indicate concentrations of SiO₂, Al₂O₃, CaO, K₂O, Fe₂O₃, MgO, MnO, and P₂O₅ are: 45.6 to 63.9 weight percent (wt. %), 15.2 to 23.6 wt. %, 0.5 to 9.1 wt. %, 1.7 to 4.6 wt. %, 2.9 to 9.0 wt. %, 0.2 to 1.5 wt. %, .06 to 1.1 wt. %,and .8 to 5.8 wt. % respectively. Trace element concentrations of Ba, Sr, and Rb are: 162 to 806 parts per million (ppm), 46 to 244 ppm, and 54 to 137 ppm respectively. Principal component analysis (PCA) plot indicates that two groupings are present in the ceramics based on comparison of axis one and axis two. Generally CaO is lower than expected since the ceramics are shell tempered but thin sections of these ceramics show void space in the shape of shell. There is good correlation of K vs. Rb, plot indicates that Rb is likely replacing K, possibly in the interlayer cation site of the clays utilized in production. Atypical amounts of P₂O₅ of greater than 1 wt. % are present in 94% (n=37) of the ceramics, which could be from post depositional alteration, the paste material or the temper. This warrants further investigation to find the source contributing to the elevation of P₂O₅. The five ceramics within PCA group two all contain at least 600 ppm Ba and greater than 145 ppm Sr. These chemical trends seen throughout the ceramics taken from the structure support that they were manufactured similarly, and contribute evidence that the structure was used for ceramic production.