Shibuichi

Shibuichi (四分一) is a historically Japanese copper alloy, a member of the irogane class, which is patinated into a range of subtle greys and muted shades of blue, green, and brown, through the use of niiro processes, involving the rokushō compound.

In addition, the metal in general, and especially the paler shades, may be named rogin.

[citation needed] The first official mention of the material is from the early 18th century, in documents from the State Mint, though it is believed to have existed before that.

For most of its history, shibuichi was mostly used to ornament various fittings for Japanese swords until the Meiji reforms, when most swordmakers began to make purely decorative objects instead.

Similar alloys have been used elsewhere but the use of shibuichi to achieve different colored patinas appears to have remained nearly unknown outside Japan, until recent interest from artisans in the West.