The ash made by burning sheep’s tooth leaves has been used as a fluxing agent for glazes in the East since ancient times. The “Pottery Illustrations” in the “Pottery Theory” describes a type of fern called “hooi-sao” that is said to be a type of sheep’s tooth.
According to Fujie Nagataka, the phosphoric acid contained in the ash makes the Gosu dyeing process more vivid and elegant.
