shakudo; gold-copper alloy with blue-black patina
A traditional Japanese alloy of copper and a small amount of gold, often treated to develop a rich blue-black or purple-black patina. Used in sword fittings, jewelry, and decorative metalwork.
The tsuba of this sword is made of shakudo.
The distinctive blue-black color of shakudo is produced through a patination process called niiro finish.
The term 赤銅 (shakudō) literally means 'red copper', though the alloy is known for its blue-black patina. The name likely refers to the copper base or the reddish color before patination. The exact historical origin of the term is uncertain.