karat or carat

1

See also fineness of precious metals.

A unit of proportion indicating what part of an alloy is precious metal. Pure, unalloyed gold is 24 karat; 12-karat gold is ¹²/₂₄, or 50% gold, and so on. In the United States it is spelled with an initial “k,” to distinguish it from the carat, a unit of mass, but in most of the world it is spelled with a “c.”

The word is from the Arabic qirat, which represented the ratio ¹/₂₄ much as in English the word “nail” used to represent ¹/₁₆ of a larger unit, sometimes ¹/₁₆ of a yard and sometimes ¹/₁₆ of a hundredweight. In Lebanon today, for example, one kirat is ¹/₂₄th of a drah. (UN 1966)

Pure gold is quite soft and not suitable for objects like rings; a ring is made of 18-karat gold alloy to improve performance, not to save on the cost of materials. Alloys below 14 karat, however, are liable to crack.

Gold Alloys Permitted in England
Period Legal Fineness
in carats
1477-1575 18
1575-1798 22
1798-1854 18, 22
1854-1932 9, 12, 15, 18, 22
1932 9, 14, 18, 22

sources

First, that the purest gold containes foure and twentie caracts in the ounce, and foure graines make a caract. ...

Now I returne to the discourse in hand. Queene Elizabeth in the yeere 1600, contracted with the Mint-Master, that of gold of the standard of twenty three caracts three graines and a halfe, he should coyne pieces of Angels, halfe Angels, fourth parts of Angels, pieces of an Angel and a half, & of 3 Angels. Now this Angel was of three pennyweight and 8 graines, and this gold was commonly called Angel gold. Also she contracted with him, that of gold of the Standard of twentie two caracts, he should coyne pieces of twentie shillings, and pieces of tenne shillings, and pieces of five shillings; and the piece of tenne shillings was three pennyweight fifteene graines. And this gold called Crowne gold, was almost two caracts baser then the former, ...

Fynes Moryson.
An Itinerary containing his ten yeeres travell through the twelve dominions of Germany, Bohmerland, Sweitzerland, Netherland, Denmarke, Poland, Italy, Turky, France, England, Scotland & Ireland.
Glasgow: James MacLehose and Sons, 1907.
Part I, Book III, Chapter 6.
Pages 133-134 of volume 2 of this edition. The first edition was published in 1617, but the travels took place between 1591 and 1603.

2

In German-speaking Europe, the Karat of Cologne, a unit of mass used for gold and silver, = ⁹⁄₁₆₀ Quentchen, about 205.5 milligrams. In Frankfurt am Main, however, 1 Karat = ¹/₁₁₅₆ Mark, about 205.8 mg. Article 4 of the law¹ establishing the metric system in Austria specified that the Wiener Karat (Vienna karat) was equivalent to 205.969 gram.

Gesetz of 23 July 1871, R.G.B 1872, No. 16. The law is reproduced in
Georg Thaa.
Das Mass- und Gewichtwesen und der Richdienst in Österreich.
Volume 13 of Taschenausgabe de Österreichischen Gesetze.
Vienna: Munz'sche k. u. k. Hof- Verlags- und Universitats-Buchhandlung, 1900.

3

In Norway and Denmark, a unit of fineness of precious metals, = 1/24 mark = 4 gran = 12 gren, about 4.17 %.

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