A suribachi is a Japanese mortar.
It can come in a wide range of sizes, anywhere from 10 to 30 cm (4 to 12 inches) wide.
Suribachi are typically made from ceramic. Inside the bowl, they are ridged and unglazed. Outside, they are glazed, save for the bottom, which helps it to slide less.
They also come made from plastic now.
The ridges inside help to grind things up more easily. There are several standard patterns for the ridges: circular pattern, daisy-wheel or what looks like commas. The ridges are called “kushi-no-me.”
The pestle is called a “surikogi.” It is made of wood, so that the ridges in the ceramic bowl don’t get worn down. Traditionally, the pestle was made from thick branches from the Japanese Prickly Ash tree, the same tree that the spice sansho comes from. The bark was left on, so that some of the spice taste would go into the food. Now, surikogi are made out of wood such as cedar turned on a lathe.
New ceramic ones should be rinsed with hot water and dried before use, to remove any clay dust.
Suribachi originated in southern China. They were introduced into Japan sometime in the 1100s.