ELEVATED PHOSPHOROUS CONCENTRATIONS IN MIDDLE OHIO RIVER VALLEY FORT ANCIENT CERAMICS: ARE BONE INCLUSIONS THE SOURCE?

The study of prehistoric ceramics can provide insights into ancient manufacturing techniques. Evaluation of a sample of Fort Ancient ceramic body sherds with high phosphorus concentrations from three multicomponent Fort Ancient sites in the Middle Ohio River Valley lead to the discovery of a bone inclusion in the paste of one sherd. In the past, researchers have explained elevated phosphorus levels with reference to source materials, use, or post-depositional alteration. Hence, a petrographic and chemical study was undertaken to test whether bone inclusions could explain elevated phosphorous in the ceramics. Representative specimens were analyzed using the petrographic microscope, SEM/EDAX, and XRF. All ceramics examined petrographically (N=9) contained bone-like. Therefore, two samples from each site were evaluated with the SEM for morphology, and the EDAX system was employed to develop elemental maps. The maps indicated that these inclusions were composed only of Ca and P, which are major components of bone; these also were the only locations of concentrated phosphorous. Based on these results, all of the ceramics were analyzed for major and trace elements using the XRF. The phosphorous content for the ninety ceramics ranged from 0.62 to 5.73wt%. In contrast, the highest concentration for the soils from the three sites was 0.67 wt%. The XRF results, coupled with the EDAX elemental mapping, confirm that the elevated phosphorous was from point source inclusions of bone. These results suggest that bone fragments were intentionally or accidentally added to the paste of Fort Ancient ceramics. These results suggest researchers should also consider bone as a source of elevated levels of phosphorous. This study also raises interesting questions concerning how and why prehistoric potters added bone fragments to their ceramics.