Gosu (cobalt blue pigment)
The cobalt-based blue pigment used in sometsuke (blue-and-white) underglaze decoration on japanese porcelain. Gosu was originally imported from China and later produced domestically, enabling the blue-and-white tradition that defines Arita, Hasami, and Seto porcelain.The photo features a Shigaraki ware mug adorned with lines hand-painted in Gosu.
FAQ regarding Gosu (Cobalt Blue Pigment)
Q. What exactly is the "Gosu" used in pottery?
Gosu is a traditional, mineral-based blue pigment containing elements such as cobalt, iron, and manganese.
Before firing—at the bisque-fired stage—it looks like nothing more than a dark, dull grayish mud or liquid. However, once a clear glaze is applied over it and the piece is fired in the kiln at high temperatures around 1,300°C (2,370°F), it dramatically transforms into a beautiful, vibrant indigo blue. Porcelain or pottery decorated with Gosu under the glaze is known as Sometsuke (blue and white ware), a celebrated style represented by Arita and Hasami wares that is cherished worldwide.