Tenmoku-yu is a traditional Japanese high fired iron-oxide glaze that produce a dark colour. The name “Tenmokuyu” is derived from the so-called “Tenmoku” tea bowls from the Song dynasty (960–1127 AD). During the Muromachi period (1336 to 1573), Japanese potters tried to imitate the Chinese stoneware Jian ware (建盏) of the Song dynasty. The Japanese term gradually replaced the original Chinese one to name wares of this type.
The Tenmoku-yu glaze has a distinctive dark, mottled colour that lightens to a reddish brown, depending on application and firing. The technique was introduced in Europe when ceramist Bernard Leach returned to England after 11 years spent in Japan.