| Many modern owners see the coloration as tarnish and clean the surface, but it was probably intended to imitate the Japanese dark-colored alloys shibuichi and shakudo. |
| As a rule, the finest kozuka were of high-grade shakudo or shibuichi with gold overlay and inlay. |
| The dark-painted rim and foot imitate Japanese cloisonne enamel vases, which often feature dark rims and bases of shakudo, an alloy of antimony, copper, and gold. |
| A rectangular front plate was formed from a thin sheet of metal such as low-grade shakudo or other lower-quality mixed metal. |
