This black kokudei Tokoname-yaki yuzamashi (湯冷まし - water cooler) has a wide opening, providing a large surface area for the water to cool quickly.
Yuzamashi are used to cool down boiling water to a temperature more suitable for brewing green tea. When poured into a yuzamashi, boiling water cools to roughly 90°C, which then will cool to roughly 80°C when poured into a cold teapot. To cool water further, you can either let it sit in the yuzamashi for longer, or pour it into cups and then into the teapot.
