Sumie is one of the most popular ink brush painting techniques in Asian countries such as Japan, China, Taiwan, Hong Kong and South Korea.
The pictures drawn by Sumi (black ink) are generally called "Suiboku-ga" or "Sumi-e" in Japan. It is said that "Sumi-e" is the most popular way of saying overseas.
Sumi-e basically uses only black ink but sometimes uses a little bit of other pigments as well. (Sumi-e with other pigments is called Bokusaiga.)
Sumi-e came from China with Zen in 13th century. And after then, Sumi-e has made its own development in Japan.
About the painting techniques, the Sumie uses various techniques of gradation, shading, bleeding, blurring. Such techniques can be obtained through changing the amount of water added to the ink. I'm sure you will be absorbed in mastering this technique.