This is a traditional tea set called a Zisha pot (紫砂壺, shisa-ko), made from Zisha clay (紫砂土, shisa-tsuchi) harvested in Yixing, Jiangsu Province, China. It is known for its excellent breathability and heat retention, and is said to absorb the impurities of tea, enhancing its aroma. Because it is produced in Yixing (宜興, Gikō), it is also called a "Yixing kiln" tea set. The signature (落款, rakkan) on the bottom, as seen in the image, indicates the artist or kiln. It is also known as a tea set that "matures" as it is used over a long period, developing a luster and depth of flavor. It is suitable for high-temperature brewing of highly fermented teas such as oolong and Pu-erh.