Pure gold means that the gold content is above 99%, which is a way to express the color of jewelry. It can also be expressed as "990 gold", "gold990" or "g990". Pure gold is dark yellow, commonly known as two 9s. When selling precious metal jewelry, the material and purity should be indicated separately. Gold is a precious metal with soft texture, good ductility, corrosion resistance and high chemical stability. Gold is used in many fields, but there is no pure gold because of the extraction process. China stipulates that gold with a gold content of 99.6% can be called pure gold.

When making jewelry with gold, because gold is soft, it is easy to leave scratches or deformation, so other metals are usually added to gold to improve the hardness. This alloy of gold and other metals is called K gold.