Electrum

Electrum is a natural alloy of gold and silver, usually with traces of copper and other metals, whose colour runs from pale to bright yellow as the share of each metal changes; it has also been made artificially and sold as green gold, though it looks pale yellow rather than green. Its formal name is unsettled because the sources read give it no fixed make-up: Wikipedia defines it by a gold-and-silver mix of varying proportions, and Cunningham uses the word for any mixture of metals, naming gold, silver and platinum. Ancient Egypt used it from the third millennium BC, sometimes to coat the capstones of pyramids and obelisks, and the earliest known metal coins were struck from it. Cunningham writes that natural electrum is rare and was once highly prized in magic, and that mixing metals combines their powers, so a made alloy suits work calling on several planets at once. He retells a tale of an electrum cup that betrayed poison poured into it by throwing off rainbows and sparks, and suggests that a Wiccan honouring both Goddess and God might wear a ring or pendant of silver and gold electrum as a sign of their union. Today it is rarely sold and usually made to order.