Pure gold is 24 karat gold, which means it is 100% gold with no other metals mixed in. Lower karatages contain less gold, with 18 karat gold containing 75% gold and 25% other metals, often copper or silver. The karat of gold is used to describe the gold content of a piece of jewelry or bullion, with each type of gold karat denoting what percentage of the piece is pure gold and what percentage contains other metals. Gold jewelry is rarely 100% pure gold due to how soft the raw material is and hence how prone it is to wear-and-tear.