Abstract
The microstructure and formation process of Hidasuki, a characteristic reddish pattern on traditional Japanese unglazed stoneware called Bizen, was studied through model experiments. Pellets of the Bizen clay mined at Bizen-shi/Okayama pref. were heated to 1250°C with and without rice straw and then cooled at different rates. A reddish color pattern appeared for relatively slowly cooled samples when rice straw was present. Owing to the presence of potassium in the rice straw, mullite (3(Al, Fe)2O3·2SiO2), a major phase formed in the absence of rice straw, was replaced by corundum (α-Al2O3), hematite (α-Fe2O3), and others in the surface region of about 50μm in depth. The corundum precipitated as hexagonal plate-like crystals, and on the edges of these crystals the hematite grew epitaxially. The growth continued so that the primary corundum crystals were wholly covered by hematite to form a specific single crystalline α-Fe2O3/α-Al2O3/α-Fe2O3 structure.
