Kohiki is typically a style of dark clay body covered with thin white slip and then a translucent glaze. This style came from Korea and became popular among Chajin, who held tea ceremonies since late 16th century.
Kohiki's warm milky white as opposed to porcelain pale white is popular among collectors.
Some stains start to appear in a long run, it is called "Amamori", leaking roof. Chajins appreciated the atmosphere and the scenery of it during tea ceremonies. And the tradition continues to this date.