This small container is used for the powdered green tea which is used in the tea ceremony. Traditionally they have a special lid made for them, rather than a ceramic one. These lids were, at one time, made of ivory, but now are generally lacquered wood, or even plastic. Tea caddies of this sort are used for the 'thick' tea. They are usually enclosed in a special bag. Most tea-ceremony books illustrate both sorts of tea-caddy used.