Electrum is an alloy of gold and silver that can be found naturally in the earth. It has been known and used since the time of the pharaohs of ancient Egypt. Its lack of purity means that it is rarely used in specific rituals, but it is considered a good conductor of magic. It combines the mystical abilities of both silver and gold, in lesser strength than either pure metal but at significantly less expense than pure gold and without some of the disadvantages.
Shadowhunters are known to use electrum on some of their weapons against demons. Henry Branwell laced the fabric of Jessamine Lovelace's parasol with electrum. Isabelle Lightwood's whip is also made of electrum wire; Charlotte Branwell fought with an electrum whip as well.