Gold

Most gold used in jewelry is an alloy; and the metals added to the gold are also called "alloys."

What is a Karat? Or is it Carat?

In jewelry, the term carat (or, Karat) has a double meaning: carat is used as a measurement of weight for gemstones, with one carat weighing 1/5 gram; carat is also used in countries around the word to indicate the amount of pure gold in a piece of gold jewelry. In the United States, however, when using the word to indicate gold content rather gemstone weight, it is spelled with a "K;" hence "karat," to avoid confusion. Jewelry should always be marked to indicate how much pure gold it contains.

In the united States a karat mark, abbreviated to K or KT, indicates the amount of pure gold present in the metal. The word karat (carat) is derived from the word for fruit of the carob tree: in Italian, carato; in Arabic, qirat; in Greek, keration. The seeds of the fruit were used in ancient times for weighing gems. Also, the pure gold Byzantine coin cald the solidus weighed 24 karats. therefore, a 24 karat mark (24K or 24KT) became the mark used to indicate that something was pure gold.

To understand the concept as applied to gold, imagine that, "pure gold" is a pie into 24 equal "slices" or parts. Each karat equals one part of the pie. So, 24 KT would mean that 24 parts (out of a total of 24) are gold. In other words, 24 KT would be 100% gold; or, pure gold. In the 18 karat gold jewelry, 18 parts are pure gold and six are another metal (or, 18/24 = 3/4 = 75% pure gold); in 12 karat, 12 parts are pure gold, 12 parts another metal (12/24 = 1/2 = 50% pure gold). And so on.

I some cultures, 24 karat gold jewelry is required for certain jewelry pieces, but it's generally agreed that 24 karat, or pure gold, is too soft for jewelry use. In some parts of the world, 18 KT 0r 20 karat is preferred because of its brighter yellow color and because it is considered "purer" and more precious. In the United States, we prefer 14 or 18 karat gold because it is more durable than higher karat gold. We caution clients about the risk of high karat gold (20 KT, 22 KT, or 24 KT) for a gem-studded setting because prongs can be too easily bent open accidentally, resulting in the loss of the stones.

In some countries such as Italy, the percentage of pure gold is indicated by a number representing how many parts; out of a total of 1,000 parts, are pure gold. But it is still less expensive than platinum.

What causes skin discoloration with some gold jewelry?

Pure gold doesn't tarnish and won't discolor the skin, but alloys in the gold can corrode and produce discoloration to the skin in contact with the gold, especially under moist or damp conditions. Fats and fatty acids present in perspiration can set up a corrosive reaction, and the problem can be worse in warm, humid areas, especially where chloride (salt) is in the air.

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