Karat and Carat: A Primer.

It’s hard to imagine that two of the most important elements of jewelry are essentially the same word. Though the words are pronounced the same, they are spelled differently and are related to entirely different aspects of jewelry.

Carat (ct) relates to the weight of diamonds and other precious gemstones. This metric unit of measure was standardized in the 20th century, with one carat equivalent to 200 milligrams. Diamond carats may also be referred to as points, with one one-hundredth of a carat (0.01 carat or 2 milligrams) being equivalent to one point.

Because gemstones have different densities, their relative sizes will be different. For instance, rubies and sapphires are heavier than diamonds. Therefore, a one carat diamond will look larger than a one carat ruby or sapphire.

Carat weight is just one of many factors to be considered when choosing a precious gem. Cut, color, clarity, and shape can all impact the quality of the gemstone.

Karat (kt) relates to the purity of gold, and it is primarily an American term (see the chart below for conversion to European percentage measures). The purest form of gold is 24-karat. Jewelry is rarely made of 24-karat gold, as it is quite soft and thus not very durable.

In order to increase its durability, pure gold is mixed with other metals to create an alloy. These other metals may include silver, nickel, zinc, or copper. Each gold karat represents 1/24th of the whole. For example, 14-karat gold is comprised of 14 parts pure gold and 10 parts of another metal.

Karat Marking Gold Content Alloy Content
24K 99.99% 00.01%
22K 91.66% 08.34%
18K 75.00% 25.00%
14K 58.33% 41.67%
10K 41.67% 58.33%

 
While the majority of gold used in jewelry is yellow in color, metal alloys added to pure gold can change the color of the precious metal.  The alloys may produce white, rose, green, and still other gold hues.