Electrum

Electrum is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals. It has also been produced artificially, and is often known as green gold. The ancient Greeks called it 'gold' or 'white gold', as opposed to 'refined gold'. Its color ranges from pale to bright yellow, depending on the proportions of gold and silver. The gold content of naturally occurring electrum in modern Western Anatolia ranges from 70% to 90%, in contrast to the 45–55% of electrum used in ancient Lydian coinage of the same geographical area. This suggests that one reason for the invention of coinage in that area was to increase the profits from seignorage by issuing currency with a lower gold content than the commonly circulating metal.

Electrum was used for the earliest metal coins, and as early as the third millennium BC in Old Kingdom Egypt, sometimes as an exterior coating to the pyramidions atop ancient Egyptian pyramids and obelisks. Electrum was also used in the making of ancient drinking vessels and coins. For several decades the Nobel medals awarded with the Nobel Prize have been made of gold-plated green gold.

The name electrum was also used to denote German silver, mainly for its use in making technical instruments