Archaeometric Characterisation of Sangam-Period Pottery from Keeladi, Tamil Nadu, India Using XRF and CHNS Analysis

Abstract

This pilot study reports the elemental composition of pottery sherds from Keeladi, a Sangam-period (6th century BCE) urban settlement on the banks of the Vaigai River in Tamil Nadu, India. Ten sherds, comprising Terracotta, Black-and-Red, Red Slipped and Coarse Red wares, were analysed by X-ray fluorescence (XRF) and carbon, hydrogen, nitrogen and sulphur (CHNS) elemental analysis. The XRF data suggest that potters may have used alluvial clays from the Vaigai River basin, characterised by high concentrations of SiO2 (45.3–62.2%), Al2O3 (13.8–15.5%) and Fe2O3 (7.9–8.8%). The Principal component analysis (PCA) and hierarchical cluster analysis (HCA; Ward linkage on Z-score standardised data of 22 elements) showed broad agreement. PCA and HCA yielded comparable results. In both analyses, KLD-5 was distinctly separated from other sherds characterised by higher contents of Zr, Nb, Th, and Si. KLD-1 and KLD-6 were found close to each other, while the remaining seven sherds were grouped into one cluster according to HCA. Silhouette analysis identified the three-cluster solution as the best among the solutions tested, with a mean silhouette coefficient of 0.358. However, it can be seen that the coefficient is relatively low, which implies only a moderate degree of separation between clusters. Thus, the results suggest preliminary patterns of compositional similarity rather than strongly defined compositional groups. In the CHNS data, the three Black-and-Red Ware sherds have the highest carbon contents (0.60– 0.69%), consistent with carbon retained under reducing firing conditions. The results provide a compositional baseline for comparing pottery from other Early Historic sites in South Asia and can support future studies of ceramic provenance, distribution and exchange in the region.