As in the YongLe reign, underglaze blue was made with the imported cobalt pigment called smalt, which yields a sapphire blue speckled with black dots because of its high iron content.

• 宣德青花上承永乐，以进口的“苏麻离青”为饰，烧成后呈宝石蓝色，由于进口钴料中含有较多的铁份而呈现黑铁斑点，古雅幽靓。