This is "Sumi" (solid ink) used in calligraphy. I believe it is a type of ink called "Kansouhou" made by Kobaien, a top Japanese ink manufacturer. This ink uses the highest quality rapeseed oil soot, producing a glossy pure black in dark ink and a brownish-black in light ink. It is suitable for Kanji works, Kana calligraphy, sutra copying, etc. There is a slight chip and deformation on the upper corner. Thank you for looking.