Pure gold is naturally yellow. However, pure gold is too soft to make jewelry out of. Because of this pure gold is often combined with other metals the result is an alloy that comes in a variety of colors.
The amount of pure gold in a piece of jewelry is measure in karats. Karats get their [...]

Because gold is usually mixed with other metals to give it hardness and strength it is important to be able to determine how much of the piece is truly gold. The blend of metals is called an alloy. Karats, abbreviated Kt or K, are used as a measure of the fineness or purity of gold.
The [...]