Estimation of places of production of porcelains of unknown origins excavated at the Mietsu Naval Facility site based on differences in the solubility of trace metals during the elutriation process

Abstract More than 300 porcelains of unknown origins were excavated at the Mietsu Naval Facility site in Japan in 2009, which was designated by UNESCO as a World Heritage Site in 2015. Forty-nine representative porcelain pieces were chosen and the metals in the porcelains were identified to clarify their places of production by using the synchrotron-based X-ray fluorescence method. The metal composition of porcelains was analysed by a new method designed by the authors based on the difference in the solubility of metal ions during the elutriation process carried out during the manufacturing of porcelain. Niobium (Nb) and zirconium (Zr), which are barely soluble in water, become a part of the clay, whereas rubidium (Rb), which is highly soluble in water, easily gets discharged with the upward flow of water during elutriation. The plotting of integrated fluorescence intensity ratio of Zr/Nb vs. Rb/Nb led to the porcelains being distinguished into three groups based on their places of production: Hasami, Shida, and Arita in Hizen. X-ray diffraction (XRD) patterns of the porcelains and the XRD patterns of the powdered raw pottery stones were determined. Differences in the XRD patterns are also discussed in terms of identifying the production areas of the excavated porcelains.