There are some alloys called <i>irogane</i> in the field of traditional Japanese metal arts and crafts. They are colored by a traditional method, <i>nikomi-chakushoku</i>, and give various colors. * 2Shakudo*1, above all, has been esteemed as the representative of * 2irogane*1. It is a copper alloy basically containing 1-5% by weight gold and has a black surface. This black surface does not appear until the alloy is treated by <i>nikomi-chakushoku</i>. The present study deals with this black surface. The x-ray diffraction method revealed that the colored layer consisted mainly of cuprite. The micromorphology of the colored layer was observed with a scanning electron microscope (SEM). The colored layer was the aggregate of fine particles of cuprite; it was flexible and adherent. The distribution of copper, oxygen, and gold in the colored layer was detected with Auger electron spectroscopy (AES). These results were compared and discussed with the data of the colored layer of pure copper. Analysis with a transmission electron microscope (TEM) gave more detailed information; it will be helpful to obtain further information about <i>shakudo</i>. -- AATA