Tianqi porcelain or ko sometsuke (古染付け) refers to Chinese underglaze blue porcelain made in the unofficial kilns of Jingdezhen for a largely Japanese market in the 17th century. The term Tianqi is a reference to the era name of the reign of the Tianqi Emperor during the late Ming dynasty, but the style and the name are not limited to his reign. Over the same period the related transitional porcelain was being made.