Characterization of ancient red iron oxides excavated from the shimo-ohgibaru archaeological site in Kumamoto, Japan

To clarify the detailed features of the red bengala samples excavated from the Shimo-ohgibaru archaeological site in the late Yayoi period (2^nd to 3^rd century A.D.) from the viewpoint of materials science, colorimetric measurements, X-ray fluorescence analyses, X-ray diffraction measurements, transmission electron microscope observations, and surface area measurements of the ancient bengala samples were achieved. The ancient bengala sample was found to be high purity α-Fe₂O₃. The features of the color tone and particle size of the ancient bengala were clarified by comparing with those of commercially available bengala, Fukiya bengala, and synthesized α-Fe₂O₃. In addition, the starting materials and synthesis processes of the ancient bengala were discussed by applying the élutriation experiments of representative natural hematite and heat-treated natural iron hydroxide (Oniita).