Carat

The carat is a term used to quantify the mass of gems and pearls, and also the degree of purity of precious metals.

Definitions

Gemology carat (masa)

Mass unit used, mainly, to weigh gems and pearls, and abbreviated ct. In this sense, a carat historically accounted for one hundred and fortyva (1⁄140) part of an ounce (205 milligrams). Since 1907, with the implantation of the decimal metric system, the decimal carat is used, which represents a mass of 200 milligrams (0.2 grams), therefore 5 carats is equivalent to 1 gram.

Orphanage (purity)

Designates the purity of gold used in jewelry. In this sense, a carat (abbreviated) K or kt) represents a twenty-four (1⁄24) part of the total alloy mass of the metal (approximately 4.167 %). For example, if a jewel made with gold is 18 carats, its alloy is made of 18⁄24 (or what is the same 3⁄4) gold parts and has a purity of 75%, while a piece of 24 carats is made of 24⁄24 gold parts and therefore is of pure gold.

Etymology

Origin of carat mass

The term comes from the ancient Greek word keration (κεράτιον), which means carob (Ceratonia siliqua), because the seeds of this fruit were used in ancient times to weigh gems and jewelry due to the remarkably uniform size and weight of the seeds. When the Arabs adopted this unit of mass, the name was deformed to quirat and this was deformed to carat when jumping into Spanish.

Transition to carat purity

In the year 309 AD. C. the Roman Emperor Constantine I ordered the minting of the first solidus, a 24-carat (mass) gold coin (about 4.5 grams), integrated into the Roman duodecimal system of weights and measures as ¹⁄₇₂ of a pound, each carat or siliqua ¹⁄₁₇₂₈ of a pound. The solidus (from which the Spanish word salary), and its Arabic equivalent dinar (from the Latin denario, where money comes from), were the reference for the weight of gold until at least the XII, and its purity became the law of gold, that is, how many carats-mass (of the total 24 of the coin) are pure gold: 24 karats means 100% purity, 18 karats means the alloy contains 75%, etc.

Spelling: carat or carat

The spelling «kilate» is incorrect and is not accepted by the Royal Spanish Academy of Language, as the word is not related to the prefix kilo-. The abbreviation of carat mass is "ct" according to the French spelling carat, while that of carat purity is "K" due to the Greek term καθαρότητα (katharótita, “purity”).