The theme of its design of cart wheels in a stream reflects the Heian practice of soaking the wheels of ox carts in water to prevent them from drying out and cracking. A popular theme during the Heian period, this design can also be found on mirrors and the embellished paper used for decorated sutra scrolls. The exterior design comprises a ground of irregularly-shaped gold particles sprinkled densely on black urushi, on which are depicted the flowing waters and soaking cart wheels represented with gold in aogin togidashi makie and mother-of-pearl inlay. For the urushi technique of togidashi makie, metal powder such as gold or silver is sprinkled on a design executed in lacquer upon which an additional coat of lacquer is applied; after hardening, the entire surface is polished to expose the design. Aogin, a blue-tinted gold color, is a mixture of gold and silver that produces a striking, variable hue depending on the light. Raden is a technique in which materials such as mother-of-pearl are cut into a design and then applied to an object covered with urushi.