Gold's quality, in terms of purity, is measured in karats. The purest gold is not very durable; therefore, gold is alloyed with different metals to increase its strength and to change its color. Depending on the use, different purity will be favored.
Gold of the 24-karat variety represents 100 percent gold;18 karat gold is 75 percent pure; and 14 karat is 58 percent pure. When comparing gold jewelry, the higher the number of karats, the more expensive the gold. The most pure gold is not necessarily the most suitable, as pure gold is very malleable, and therefore more prone to denting and scratching.
Due to its lack of durability, 24-karat gold is rarely used in jewelry. Occasionally, 21-karat gold is used for jewelry in the United States, but it is commonly used in parts of Europe, the Middle East and Southeast Asia. A 18-karat gold is popular in high-end jewelry; whereas, 14-karat gold is the most sought-after purity for jewelry gold, as it represents a nice balance between gold content, affordability and durability. A 10-karat gold is the lowest content of gold that can be marked and sold as jewelry in the United States. It is commonly sold by chain jewelry stores, and is often used for rings due to its increased strength. Mass marketers in England often used 9-karat gold, even though this purity is not allowed to be marked and sold as jewelry in the United States.
By alloying gold with another metal, you can change its color. Gold is naturally yellow; however, even yellow gold is alloyed with copper and silver to strengthen it. The brightness of yellow gold depends on its purity. Generally, 14-karat gold has a brighter yellow than 10-karat gold and so on. White gold is alloyed with nickel, palladium, zinc and copper to give it its characteristic silver color. Rose gold is created by alloying just copper with yellow gold. Green gold is created by mixing silver, copper and zinc to yellow gold.
When buying gold jewelry, always look for the karat mark. According to U.S. law, all gold jewelry must have a stamp. In addition to the karat, the stamp should also indicate the manufacturer's trademark. Some stamps may also indicate the country of origin. The stamp provides assurance that you are buying genuine gold jewelry.
Gold bullion is investment-grade gold. It is usually purchased in the shape of coins or bars. Coins and bars can be purchased in different weights. The purity of gold bullion ranges from 22 karats to 24 karats. Like jewelry, to guarantee authenticity gold bullion must have a stamp that clearly indicates the manufacturer and the purity.