The ultimate precious metal. Virtually indestructible, amazingly malleable, doesn't rust or tarnish. Graded by purity; in the U.S. a scale of 24 is used, so 24 Karats (24K) is 100% pure. 18K is 18 parts gold and 6 parts alloy (other metals), and so on. 10K is the legal minimum for Karat-graded gold. The word "Plumb" indicates the exact purity of the piece.