[M-ZZ42] Geology and culture

[MZZ42-P02] Grinding surfaced structure (Hobo) of the Tosa-suzuri inkstone in Mihara Village, Hata Area, Kochi, SW Japan

*Nakamura Riko¹, Go-Ichiro Uramoto¹, Misa Kamimukai¹, Kazuya Iki², Maya Adachi², Osamu Tadai³, Yohei Hamada⁴, Wataru Tanikawa⁴, Takehiro Hirose⁴ (1.Kochi University , 2.Cooperative for the Mihara-suzuri Inkstone, 3.Marine Works Japan, 4.JAMSTEC)

Keywords:Tosa-suzuri inkstone, Hobo, Mihara Village

The Inkstone, together with the inkstick, ink brush, and paper, is called as the Four Treasure of the Study. It is used to grind solid inkstick with water into liquid ink and has important cultural values for calligraphy and brush painting in East Asian countries. On the surface of the inkstone, it has fine protruded structure called Hobo for grinding inkstick and it has been considered that the morphology and the arrangement of the Hobo are critical for making high-quality liquid ink. However, scientific investigation on the Hobo has not been conducted and the property of the Hobo is still equivocal. This study conducted the petrological and mineralogical analyses on the Hobo of the Tosa-suzuri inkstone, which is one of traditional crafts made from slate occurred at the Gendani Quarry in Mihara Village, Kochi Prefecture, SW Japan and compared the analytical results with the inkstones made from slates occurred such as along the Shimonokae River in Tosashimizu City, Kochi. X-ray diffraction analysis of the bulk studied slate revealed that the main component mineral of the slate is muscovite, quartz, plagioclase, and chlorite. Combined measurements and analyses on the surface of the Tosa-suzuri inkstone by Micro-CT, SEM-EDS, and confocal laser scanning microscopy showed two-scales of the protruded structure: (1) tens to hundreds micrometer-scale rough structure due to the edge of cleavage of the clay minerals and (2) micrometer-scale sharp-edge of quartz and clay mineral grains. It is interpreted that the micrometer-scale structure constitutes the Hobo and is critical for finely abrasing the inkstick, which is an important property of the inkstone. In contrast, the surface protruded structure on the inkstone of some “hard” slates is mainly comprised by the edge of quartz grains, resulting in rough and hard surface and not suitable for grinding inkstick. Compared with the inkstone of the mudstone, Tosa-suzuri inkstone harbors finer surface structure for making better quality inkstone.