Japanese Sumi Inks are natural vegetable based inks. Traditionally the ink is made by grinding a stick of dry concentrated ink with water and a suzuri stone. Water is added to the sloped indentation in the suzuri stone, which is made of an abrasive stone material and the ink stick is ground into the solution by rubbing it against the suzuri stone. For convenience you can also use liquid sumi ink (Bokuju) which is essentially the same ink, but has been prepared for you. The Yasutomo KF series is more water resistant and may have a slight sheen to it. The KY series of ink is more matte, but will be less water resistant.