Gold has long been symbolic of wealth and good taste, but pure gold is a poor choice for everyday jewelry. Gold is a soft metal which is easily scratched or otherwise damaged, so jewelers long ago learned to mix pure gold with other metals in order to increase its durability without ruining its value. To keep track of how much gold was used, they developed the karat system which we still use today. Two very popular blends for jewelry are 10kt and 14kt.
Karat vs. Carat
Although these words are interchangeable in most parts of the world, karats and carats are two different measures in the United States. The word "carat" is used as a measure for gem stones, such as diamonds, while "karat" is reserved for the measurement of gold purity. It might be more correct to think of a karat as a percentage of gold weight, since pure gold is so soft and is generally mixed with other metals called alloys.
In order to label a piece of gold jewelry's purity, pure gold is divided into 24 parts or karats. Why this unusual measure was originally created is unknown. Historically, the karat derives from the use of carob seeds to measure weight; perhaps 24 seeds became a standard for some symbolic reason. Gold that is 100 percent pure is 24kt gold; lesser levels of purity are expressed with smaller numbers. For example, 18kt gold is 75% pure, or 18 parts out of 24.
One of the great advantages of using alloyed gold to make jewelry, aside from the extra strength gained from the alloy, is the added ability to add different colors to the gold. While many people only want yellow gold, there is a large market for white and rose gold; these colors are created by choosing metals with different colors for use as the alloy. Copper, silver, zinc, nickel, or palladium might be used; in addition, white gold is often given a rhodium plating to accentuate the white color.
Gold labeled as 14kt is 58.3 percent (14/24) pure gold; the remaining 41.7 percent is an alloy, typically bronze. 14kt gold is brighter than 10kt gold, and is often used in more expensive jewelry as a compromise for those not wishing to pay for 18kt gold. It is also considered an ideal purity for rings and wedding bands, since it is strong and will not tarnish easily.
Gold labeled as 10kt is 41.7 percent (10/24) pure gold; the remaining 58.3 percent is an alloy, again typically bronze. Notice that the percentages are reversed. The commonly held knowledge is that 10K gold is more resistant to dents and scratches because the added alloys are harder than gold, but that is not a universally accepted fact. 10kt gold is popular for lower-priced jewelry such as class rings.