The modern version was developed in Japan, but a very similar alloy appears to have been used in ancient Egypt. Most commonly the mixture is 4 or 5% gold, but may be as much as 10%. Sahkudo is used primarily for small decorative objects, such as the cross-guard (tsuba) of a sword and, today, in jewelry -- large objects that claim to be shakudo rarely are, because of the cost of the gold. The dark color is actually a patina (the metal itself is copper-colored) that does not develop naturally but rather is created by heating with a patination agent. The modern name is, natch, Japanese, from shakudō (赤銅), meaning "red copper."
Next week we'll start working with shakudo and shibuichi, and the various ways they can be colored.