A semi-quantitative archaeothermometer based on feldspar and volcanic glass compositions in ancient ceramics from the Kibi region, Japan

In this study, we analyzed the chemical compositions of feldspar and volcanic glass clasts in haniwa from kofuns and Sue ware from the Sabukaze kiln site, both in the Kibi region, southwestern Japan, to estimate the thermal conditions of ceramic firing in the 5th–8th centuries CE. Based on the coexistence of molten and unmolten feldspar rims, the solidus temperatures were estimated at ∼ 1050°C–1150°C for haniwa and ∼ 1150°C–1200°C for Sue ware. Volcanic glass compositions changed systematically during firing, showing increases in K2O and decreases in Na2O. From these observations, we propose a semi-quantitative archaeothermometer using variations in the K/Na molar ratio of volcanic glass within a ceramic matrix. This approach can be applied to investigate the development of kiln-firing in the Kibi region, the existence of haniwa potters employing different firing methods, variation in heat input for producing Sue vessels of differing sizes or functions, and temperature-controlled practices in Sue ware production.