This is a bottled Chinese painting ink. It is convenient and of good quality. Students in my class got it in my first class.
This ink is very condensed. I drop it into a plate and dilute with water until I get the desired darkness. Usually in time ink with 3 to 4 times water you get still solid back. Dilute it on in your ink plate, do not dilute in the bottle.
Other brand of ink serves the same. Japanese or Korean ink is made with the same tradition.