Kuromido (Japanese: 黒味銅, black-flavoured copper) is a Japanese metallurgical alloy of copper with a small percentage of arsenic, traditionally around 1 percent, that develops a deep brown-black patina under appropriate chemical treatment. It is one of the family of patinable copper-alloy metals (alongside shibuichi, shakudo and rogin) used in Japanese decorative metalwork from the late medieval period onward, and is one of the principal layering metals in mokume-gane work.

The dark colour is produced not in the metal itself but on the surface, through the application of the traditional niiro (heat and patination) bath, typically containing copper acetate, copper sulphate, and rokushō (a verdigris-based patina paste). Heated to approximately 60 to 80 degrees Celsius and treated with the patina, kuromido develops a uniform dark brown to near-black surface that contrasts strongly with the warmer tones of copper, shibuichi and shakudo in mokume-gane laminated work. The alloy is somewhat softer than copper and forges, fuses, and laminates well with related alloys.

Kuromido sees most use today in studio metalwork in Japan and in Western mokume-gane practice. It is sensitive to acidic environments and the patina can be damaged by perspiration; pieces are usually finished with a wax sealer or worn intermittently. The arsenic content is fixed within the metal lattice and at conventional working temperatures presents no occupational hazard, but melting and casting should be performed with adequate ventilation.