Use of the cast iron teapot, or tetsubin teapot, became common in Japan around the time Sencha Green Tea was introduced between the 17th and 18th centuries. But originally, these Japanese tetsubins were used for boiling water, often left over the fire to keep the water hot so a cup of tea could be made at any time.
Soon after, drinking loose leaf teas became popular and the Japanese cast iron teapot was a household necessity. Much like the Chinese Yixing clay teapots, the cast iron teapots become seasoned with a tea’s flavors after repeated use.**