Mumyoi (pronounced moomyoee) is a type of pottery made from Mumyoi Clay, which contains ferrous oxide and is obtained near the old gold mine on Sado Island, a small island off of Japan’s west coast noted for its hot springs.

Unlike other pottery, Mumyoi requires extra processing efforts; raw-polish, a process that polishes the products with cotton cloth before baking, as well as a process of polishing with sand after baking. The particles of clay must be extremely fine, a quality which can only be obtained through an energy intensive filtration process using a clay-water mixture.

Mumyoi pottery is baked in a kiln at a high temperature and becomes very dense and contracts about 30% from the original size, making the finished pottery exceptionally hard. Genuine Mumyoi produces a clear metallic sound when tapped. The more Mumyoi pottery is used, the more beautiful its finish becomes.

Originally, Mumyoi was used for medicinal purposes such as relieving symptoms of palsy, digestive problems, burns, and helping to stop bleeding.

The Gyodoku Pottery maker is dedicated to the continuous endeavor of producing conventional Mumyoi pottery, developing new glaze formulas by mixing together natural and non-organic substances such as rock, stones, and the ashes of plants and trees as well as pursuing the beauty created by Yohen. Also known as a kiln mutation (or kiln effect), Yohen is a technique of kiln firing which produces varieties of colors using a climbing kiln (multi-chambered kiln) with each successive chamber at a higher (and thus hotter temperature) level than the previous.

Vessels of Mumyoi ware have been gaining popularity since they richly enhance the drinking experience of green tea, coffee, sake, and beer.