When glazed clay is fired, it expands. The high temperature melts the glaze and fuses it with the clay. When the pottery is cooled down, it shrinks...BUT, the rates of shrinkage of the clay and glaze are different. The glaze shrinks more than the clay and so during the cooling process, cracks are formed on the glaze surface. These crackle patterns are kan-nyuu. See "Kan-nyu, Those Lovely Cracks". The Ikebana Shop. Retrieved 2014-12-10.