History of Carat

The history of carat weight is one that is tied intimately the history of trade as well as the metric system. By understanding just what diamond carats are, individuals interested in buying an engagement ring or any piece of gemstone jewelry can better appreciate the value of these sparkly stones.

Carats have not always been the same size.

The word “carat” is etymologically derived from different languages’ word for “carob,” a Mediterranean seed that played an important role in trade centuries ago. The carob seeds themselves were inedible, but they were observed to have a very uniform size and weight. The seeds were then used to balance a scale when weighing precious gemstones, and a higher number of seeds indicated a heavier and therefore more valuable stone. Different countries had slightly different values for what number of seeds was equivalent to what value of gems, but the use of the seeds was consistent throughout Europe. In areas of the world where carob was not as popular, grains of wheat or rice were used in similar ways to discern the weight of diamonds.

Over time, it was discovered that despite their visual uniformity, carob seeds were not as consistent in size as previously thought and standardization of the measure for a gemstone’s weight was required. In 1907, the Fourth General Conference on Weights and Measures – an international organization responsible for metric measurement standardization consisting today of more than 70 member nations – adopted the carat as the official metric measurement for gemstone weights. One carat is defined as one-fifth of a gram or 200 milligrams, roughly the weight of a single dollar bill. In 1913 the United States accepted the carat as the gemstone measurement, and in 1914 the United Kingdom followed suit. By the 1930s, the majority of countries involved in the diamond and gemstone industry had agreed to the standard measurement.

Carob seeds are not as uniform as once thought.

One issue of particular note is how this standardization relates to antique, heirloom, and vintage engagement rings. If a ring was manufactured prior to 1913, the stated carat weight may not be accurate and the stone could be either larger or smaller when measured with modern values. While older rings are generally more valuable because of their other properties – design, styling, and sentiment, for example – a couple interested in purchasing an older ring should have it professionally appraised and accurately measured before agreeing on a sale price.

When the history of carat weight adjusted to the standardized measurement, additional quantifiable measures were needed to compare stones of different weights and partial carats. A carat weight is expressed in points, with one full carat being equal to 100 points. A quarter carat stone, then, is 25 points. For grading purposes and diamond certification, gems are measured to three decimal places, though that measurement may then be rounded to two decimal places for convenience. A half carat stone, then, may be measured as .498 carats but rounded to .50 carats. The jewelry industry maintains strict regulations on the ranges of carat weights that may be grouped into particular fractions to help uphold the high quality standards of the industry.

Because the carat is a measure of weight rather than size, two stones that have identical carat weights may actually appear very different depending on their exact geometry, proportions, and shape. In general, compact shapes such as round diamonds appear to be the smallest based on a comparison of carat weight and visual size, whereas longer gems such as emerald cuts or marquise shapes maximize the stone’s table with the illusion of greater size for the same carat weight. There is a sacrifice to that optical illusion, however: longer diamond shapes tend to have less brilliance and may reflect shadows or dark spots in their interior because of the irregular reflection and refraction patterns.

After a diamond is mined it may be measured to weigh several carats, but that is only the beginning of its processing. As the stone is cut into a jewelry quality shape, between 40 and 60 percent of its mass will be lost, resulting in a much smaller carat weight. This reduction is part of the reason why there are many more small diamonds and gemstones and why large carat gems are much more valuable and rare. The prices of larger gemstones increases exponentially based on carat weight, meaning that a full carat diamond is more than twice as expensive as a half carat stone. This makes carat weight one of the most important factors in diamond prices, though the other Cs of diamond quality – cut, clarity, and color – have a significant impact on the value of a diamond as well.

Understanding the intricacies of the history of carat weights and how they apply to engagement rings can help couples find the perfect ring for their budget and style preferences without being fooled by its numerical values.

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