Electrum is a naturally occurring alloy of mainly gold, silver, sometimes trace amounts of copper, and other minuscule impurities. Ancient Greeks called it 'white gold' as opposed to 'refined gold', because its color(s) were more pale than 'refined gold', which tended to be a yellow color. This metal alloy was also used in currency from the Byzantines, to the Lydians, and the Middle Eastern countries like what is now Turkey. The Amounts of Electrum per coin varied from the Empire which used it. The Lydians used only 45% to 55% electrum coins compared to Anatolia's 70% to 90% electrum coins. The more it was used, the sooner it became known that it was in fact an alloy and could be artificially recreated, and that is when it was used for coinage.