Greenware is also closed entwined with white porcelain. The glaze with a mixed subtle colour gradations of icy, bluish white is called "seihakuji" (青白磁) porcelain. In Chinese this type of glaze is known as Qingbai ware. Qingbai's history goes back to the Song dynasty. It is biscuit-fired and painted with a glaze containing small amounts of iron. This turns a bluish colour when fired again. Japanese artists and clients tend to favour the "seihakuji" bluish white glaze over the completely green glaze.