The tools which are essential are called the Four Treasures. These are the brush, ink, ink stone and paper. Special brushes made in East Asia are used. The ink is not ink at all but consists of a formula of soot and glue made into a stick by a special process. This in turn is rubbed in water on an ink stone and forms what is called black ink, "sumi", in Japanese. The paper may be machine or hand made and is generically called rice paper.