Pottery has been produced in the city of Tokoname, Aichi prefecture, as far back as the 12th century, and since 1976 has been protected as a Traditional Craft of Japan. Tokoname was the site of the largest and oldest of the legendary Rokkoyō (六古窯): the “Six Ancient Kilns” of Japan, and is celebrated for its iron-rich Shudei clay that turns a bright red after firing. When fired a second time in a reduction oven, the red Shudei turns black – another characteristic colour of Tokoname-yaki. High-fired at temperatures of around 1100°C and left unglazed (Yakishime, 焼き締め), this allows tannins in the tea to interact with the iron in the clay body, which is said to reduce astringency and highlight the sweetness of green teas. Another key feature of these Kyusu are the perfectly fitting lids, which are ground into the clay body after firing in a technique known as Suriawase.