indigo wax inkstick
A type of solid inkstick made from indigo wax, used in calligraphy and painting. The term refers specifically to the stick form, not the liquid ink.
I grind an indigo wax inkstick to make indigo ink.
Compound of 青 (ao, 'blue/indigo') and 墨 (sumi, 'inkstick'). The exact historical derivation is uncertain, but the term describes the indigo color of the wax-based inkstick.