Irogane

Irogane (色金 "coloured metals") is the term for a set of Japanese metals – forms of copper (with natural impurities), and copper alloys – treated in niiro patination processes, traditionally used in sword-making, catches for sliding doors, and luxury highlights on larger objects, and in modern times, in jewellery. The alloys contain two to five metals. Some scholars believe that methods similar to those involved in irogane production may also have been used in ancient Egypt and the Roman world, as well as China (wu tan) and Tibet (dzne-ksim).^{: p. 125}