Kannyu
Kannyu (Japanese: 貫入) is a ceramic glaze effect characterized by a network of fine cracks that appear on the surface of glazed pottery. The crack patterns form naturally when the glaze and the clay body contract at different rates during cooling after firing.
In ceramics, glazes and clay bodies expand and contract as temperatures change. If the glaze contracts slightly more than the underlying clay during cooling, tension develops in the glaze layer. This tension can produce a network of small cracks known as crackle or crazing. In Japanese ceramics this effect is often referred to as kannyu.
The crack patterns may appear as fine lines across the glaze surface and can vary in density and size depending on the composition of the glaze and the firing conditions. In some cases the cracks become more visible over time as pigments, tea, or other substances penetrate the fine lines.
In Japanese ceramic traditions, kannyu is often appreciated as a decorative effect rather than considered a defect. Crackle glaze surfaces appear in several types of tea ceramics and in wares such as Hagi ware and Raku ware.
The appearance of kannyu can be influenced by glaze composition, firing temperature, and cooling speed, making each pattern unique.
