Shakudo Metalware

Shakudo is the Japanese term for a copper alloy with a low gold content of between 2 - 7% and other small additions.  3% was typical.  The aim was to produce chemically tinted finishes such as shades of grey more by control of the alloy content than by varying the composition of the colouring solution.  While the base metal of these vases and dish has lost its original patina they do show the overlay of other metals such as pure copper and silver.  The Japanese refined and made very good use of this technology up to the end of the Mejii era in 1912 but it probably originated in earlier Greek and Egyptian civilisations.

http://www.ganoksin.com/borisat/nenam/shakudo.htm