Niiro, also known as niiro-eki (煮色液), niiro-chakushoku (煮色着色), nikomi-chakushoku (煮込み着色) or niage (煮上げ) is an historically Japanese patination process, responsible for the colouration of copper and certain of its alloys, resulting in the irogane class of craft metals, including shakudo, shibuichi and kuromido. It is now practiced in a number of countries, primarily for the making of jewellery and decorative sword fittings, but also for material for hollowware and sculpture. Importantly, the same process operates differently on different metals so that a piece with multiple components can be treated in one patination session, developing a range of colours.
