In a kiln set up in a room partitioned off by shoji paper, small pieces of pine wood are burned slowly, one by one, for 100 hours, taking care not to let the spark of fire die out. The soot is collected by sweeping away from the shoji room where the kiln is set up. The size of the room is about a tatami mat. It is hard work, literally covered in soot from head to toe.
Originally, the room was partitioned by shoji paper, but nowadays, fire-resistant cloth over wire mesh are used to prevent flames.
Mr. Horiike is the only pine-soot shokunin (artisan) in Japan who makes pine-soot, the raw material for sumi ink.