Jar with Japanese hydrangea vine, Sun and Moon design in underglaze blue and overglaze enamel, gold and silver.

Blue underglaze

Blue and white porcelain (sometsuke) is made by painting blue underglaze decorations on white bisque-fired pottery using a cobalt-rich pigment known as zaffer (gosu). The piece is then coated with a transparent glaze and fired. This technique for making blue and white porcelain has been used in China since around the twelfth century during the Yuan Dynasty.