Shakudō
Shakudō ( 赤銅 ) is a Japanese billon of gold and copper ( typically 4–10% gold , 96–90% copper ) , one of the "irogane" class of colored metals , which can be treated to develop a black , or sometimes indigo , patina , resembling lacquer . 
<triplet> Shakudō <subj> Japanese <obj> country of origin <triplet> billon <subj> copper <obj> has part