Nigurome is a Japanese decorative metal alloy of copper, silver, and a small proportion of gold, developed during the Edo period (1603–1868) for sword fittings (tosogu) and ornamental metalwork. The alloy is one of the family of patinable copper-based alloys — alongside shakudo, shibuichi, and kuromi-do — that take a stable dark patina under traditional Japanese niiro chemical treatment, producing surfaces ranging from grey through brown to black. Nigurome typically carries a higher silver content than shakudo, giving its patinated surface a darker grey-black tone with a softer character than shakudo's distinctive purple-black.

Composition and patina

Recipes vary by school and workshop, but nigurome generally contains roughly seventy to eighty per cent copper, ten to twenty per cent silver, and a small proportion of gold (often one to three per cent). The alloy is melted, hammered, and worked to the desired form, then patinated by immersion in a niiro solution containing copper acetate (rokusho) and other compounds, applied with controlled heat. The reaction produces a thin, stable copper-silver-sulphide oxide layer that gives nigurome its characteristic dark grey-black appearance.

Use in mokume-gane and contemporary jewellery

Nigurome appears most often in mokume-gane work, the laminated mixed-metal technique developed in seventeenth-century Japan in which alternating layers of contrasting metals are forge-welded, twisted, and worked to produce wood-grain patterns. Contemporary mokume-gane jewellers — most notably American studio metalsmiths Steve Midgett and James Binnion, and Japanese workshops continuing the tradition — use nigurome as one of several traditional Japanese alloys to provide tonal contrast against shakudo, shibuichi, fine silver, and gold. Compared to shakudo, nigurome offers a distinctly different shade of dark surface, useful for layered compositions where multiple tones of dark metal are wanted.

In the trade

Nigurome is less common than shakudo in the contemporary jewellery trade and is rarely encountered as a stand-alone alloy outside specialist Japanese-influenced studio practice. Buyers of mokume-gane and Japanese-style mixed-metal jewellery may see nigurome listed in piece descriptions; the alloy carries no separate hallmark or precious-metal disclosure obligation under most jurisdictions, since the gold content is decorative rather than fineness-bearing. Care for nigurome surfaces is the same as for any patinated copper alloy: avoid abrasive polishing, mild chemicals, and prolonged contact with chlorinated water.

Further reading

• Metropolitan Museum of Art — Japanese sword fittings and decorative alloys
• Victoria and Albert Museum — mokume-gane and Japanese metalwork
• International Gem Society — patinated jewellery alloys