The weight of diamonds today is reckoned by the “carat,” a term which means different quantities of mass in different countries, though it is practically the same in those markets of the world where most of the gems are handled. It is nowhere recognized by a government as a definite legal weight, but is an evolution, peculiar to the diamond trade, out of ancient and primitive conditions. According to Charles Edward Guillaume of the International Bureau of Weights and Measures at Sevres, as reported from the Commission of the National Bureau of Weights and Measures in France, during the late endeavor to establish an international decimal weight for the weighing of diamonds and other precious stones, there exists at present, the following variations in the milligramme weight of the carat in different cities and countries :
East Indies 205.5
Pearl carat 207.2
The carat of 205.5 milligrammes, it will be noticed, is used in the chief centers of the diamond trade, and it is the weight in use in the United States. One of these carats equals four grains avoirdupois or 3.174 grains troy, and 151.42 carats equal 1 ounce troy.
With the extension of the diamond trade during the last twenty-five years, these variations have proved confusing, and an effort has been made in Europe to abolish the old system of carat weight with its divisions by two into 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, and establish a decimal system on a base of 200 mgs. as the metric carat. The dealers in diamonds, however, feared that such a radical change would disturb trade, and the at-tempt failed. Governmental recognition of the carat as a weight was sought in Germany, but the proposition could not be entertained, as it was contrary to the laws in force regarding the metric system. It is now pro-posed to substitute for the carat now in use, one standard carat weight of 200 milligrammes, leaving the metrical divisions to be acquired gradually, as the trade becomes familiarized to the idea. On October 17, 1890, the Association of Diamond Merchants of Amsterdam, fixed the value of the carat on a basis of 1 kilogram = 4,875 carats, which is practically the same as the old Amsterdam carat value.
The origin of the word ” carat” is obscure. It is said to have been derived from ” kuara ” (sun) an African tree whose fruit and blossom are of a golden color. As the bean when dried was always of about the same weight, it was used in Shangallas, the chief market of Africa in Galla-land south of Abyssinia, as a standard of weight for gold. Others trace it to the ” keration,” a word taken from the Greek by the Romans, which they described as the name of a very small weight or measure. An old book says, ” Monardus writeth that he saw diamonds in Bisnager (Visnapour) that weighed one hundred and forty ceratia, and every ceratium weighed four grains.”
Mr. Leonard J. Spencer, assistant in the Mineral Department of the British Museum, who has made a very interesting appeal for the adoption of the metric system, favors the theory that the word and weight are derived from the seeds of the Ceratonia Siliqua (carob or locust tree). He found that the seeds of this, and those of the Erythrina Corallodendron (Linn) aver-aged alike in grams 0.197, but that the seeds of the latter in the various species were not so constant as those of the former. Kuara is a native African name for a species of Erythrina or coral tree. A Greek word refers to the horn-like shape of the fruit pods of the ceratonia, whereas ” carat ” is an obsolete English name for the seeds. It seems probable that the seeds of both had an influence in establishing a certain amount of mass as a quotable weight which finally became known definitely as the carat. According to writers of the seventeenth century, the carat was divided into four grains, but they were not the ordinary grains of standard weight, nor do they appear to have been reckoned as equivalents of any standard weights outside of the trade. In the eighteenth century, 150 carats were considered equal to about one ounce troy. In the early part of the nineteenth century, the weight was established more definitely in England as 151% to 151 1/2 carats to the ounce troy. The weight decreased in value evidently as the things it weighed became more generally recognized as precious. The Greek weight (ceratium) and the Roman siliqua were a little heavier than our present carat (3,174 grains troy), as they were equivalent to 31/3 grains.
Whatever the origin, or however it may have been used in India or by Indian merchants in their trading with foreigners within or without the borders of their own land, the weight does not appear to have been adopted in India as a standard. Early travelers in India found the ” rati ” or ” ruttee ” and the ” mangelyn,” to be the weights generally used. The rati also had its origin in a seed; that of Abrus precatorins (Linn). Evidently weights bearing the same name varied materially in value in India, not only at different times, but at the same time in different principalities, as they do yet. The rati varied from about 1.85 grains to 2.49 grains. In Sambhulpur it was equivalent to about 1.86 grains. The ruttee of India now, for pearls, equals 2.85 grains, but in Delhi, for gems and the precious metals it is equivalent of 1.25 grains : in Surat = 1.95 grains ; Bengal = 2.25 grains ; Sindh = 2.49 grains. Tavernier rated a rati at 7/8 of a carat, which, if he used the French carat, would equal about 2.78 grains.
The ” mangelin ” or ” mangelyn ” of Golconda and Visapur was equivalent to 1 3/8 carats.
The oitava of Brazil equals about 17 1/2 carats or to be exact, 55.34 grains. The grao is .77 grains, or about 1/4 of a carat.