Shakudō

Japanese copper and gold alloy

Shakudō (赤銅) is a Japanese billon of gold and copper, one of the irogane class of colored metals, which can be treated to develop a black, or sometimes indigo, patina, resembling lacquer. Unpatinated shakudō visually resembles bronze; the dark color is induced by the niiro artificial patination process, involving boiling in a solution, generally including rokushō.

This keyword could refer to multiple things. Here are some suggestions: