Blue Cast Iron Osaka Teapot 20 OzUnity Cast Iron Osaka Teapot Blue finish. An elegant, distinctly shaped cast iron Tetsubin teapot named after the beautiful and ancient city of Osaka, Japan. Inspired by highly prized antique Japanese cast iron teapots still in use today. Features a black porcelain enamel interior coating that helps prevent rust. Includes a stainless steel tea brewing basket for ease of preparation for brewing and serving tea. Not intended for stovetop use. 20 oz.