The Diamond 4Cs: Carat Weight

Art. 197

The Diamond 4Cs: Carat Weight
As with other 4Cs of diamond (color, clarity, cut), carat weight is a crucial value factor. Most people know that there is a relationship between the carat weight of a diamond and its price. The diamond's price per carat tends to increase sharply with the size of the diamond because of the rarity of larger diamonds. Still, there are two important things to know about the diamond's carat weight: the first thing is that weight and size are not synonyms. The second thing is that bigger does not always mean better in terms of beauty and value. Why? Let's go find out.

What is Carat Weight?
Carat (abbreviated "ct") is an international unit of measurement that describes how much diamonds and other gemstones weigh. Carat is defined as 1/5 of grams, or 0.200 grams, or 200 milligrams. 1.00 carat can be divided into 100 points. So 1.00 point is one-hundredth (1/100) of a carat (0.01 ct). You can think of carats as dollars and points as pennies. For example, $ 1.25 means 1 dollar and 25 cents, and 1.25 carats means 1 carat and 25 points. In the market, many diamond professionals and jewelers often refer to the carat weight of diamonds in terms of points, especially for diamonds that weigh less than one 1.00 carat. For example, 0.25 carats would be described as "twenty-five point" or "twenty-five pointer." Diamonds that weigh greater than 1.00 carat are expressed in carats and decimals, so a 1.05-ct stone would be described as "one point oh five carats" or" one oh five."

Carat weight should not be confused with the karat (abbreviated "kt"), as in "18K gold," which is a unit of measurement used to describe the purity or fineness of gold.

History of Carat Weight
The modern carat system sprouted from the tiny carob seed that comes from the locust tree. Early gem traders and jewelers used the carob seeds as a counterweight in their balance scales. They have a relatively uniform size and weight (averaging about 0.197 grams). In the early twentieth century, the carat was standardized as 0.200 grams, giving trade members a uniform and universally accepted unit of measurement to describe gem weight.

Diamond Size vs. Carat Weight
Carat is often used as a synonym of diamond's size, but they are different characteristics. The weight of a gemstone depends on its density (mass per unit of volume), so two gemstones with distinct densities but the same carat weight may have different sizes. For instance, sapphire that belongs to the corundum mineral species has a greater density than diamond, so, with the carat weight and shape being equal, a sapphire will appear smaller than a diamond. On the other hand, emerald that belongs to the beryl mineral species has a smaller density than a diamond, so that 1.00-ct emerald will appear larger than a 1.00-ct diamond.

Another crucial factor regards the way a diamond is cut because it may influence its perceived size. Depending on their proportions, two diamonds with the same shape and carat weight may appear larger or smaller in diameter. For instance, a 1.00-ct poorly cut round brilliant diamond may appear larger than a 1.00 ct well-proportionated round brilliant diamond if it is too shallow, or it may look smaller if it is too deep or with a too thick girdle. On the other hand, a poorly cut 1.00 ct diamond may appear to have the same size as a well-cut 0.80 ct because the first can hide extra weight typically in or below the girdle, which once the diamond is set, you will not be able to see. Because more weight equals more money, the cutter tries to retain as much weight as possible from the rough, but this does not always benefit the diamond beauty.

The advice is to don't use the carat weight alone to estimate the diamond's size. Look at the cut grade on the diamond's gemological report for round brilliant diamond to make sure it is well cut and you are not paying for an overweight stone.

Carat Weight and Diamond Value
Larger diamonds in nature are rarer and so more valuable than small ones. So, all other quality factors being equal, a 1.00-ct diamond would be much more valuable than four 0.25-ct diamonds put together. At the same time, two diamonds of equal carat weight can have very different prices depending on the other diamond's 4Cs: color, clarity, and cut. For example, a 0.50-ct D-color Flawless diamond with an excellent cut is worth many times more than a 1.00-ct N-color SI2 diamond with a poor cut.

So the per-carat price of a diamond increases as the carat weight increase if the other quality factors are the same. But the price of diamonds does not increase proportionately. A 4.00-ct stone will not cost four times a 1.00-ct diamond. At certain weight boundaries, such as half-carat (1/2 ct), three-quarter carat (3/4 ct), one carat (1.00 ct), called "magic sizes," the per-carat price increases significantly, especially at the magic 1.00-ct size. That's because these magic sizes are trendy in the trade and highly demanded. For this reason, a 0.96-ct diamond will cost considerably less than a 1.02-ct diamond with the same color, clarity, and cut grades, even if the difference in terms of size is almost invisible. This aspect can help people who want to get a good-quality diamond at a more affordable price.

How is Carat Weight determined?
Because even a tiny difference in a diamond's weight can make a considerable difference in cost, precision is crucial. In the diamond industry, loose diamond's weight is determined using precise and accurate electronic balance scales. According to precise trade rules, the carat's weight is measured to the hundred-thousandths of a carat and rounded to a hundredth. So the weight of a diamond is stated in carats to at least two decimal places, for example, 1.05 carats.

Carat Weight and Diamond Value: final notes
Carat weight is one of the most crucial diamond value factors. Diamond's value increases with the carat weight because larger diamonds are scarce, but this is true if other quality factors are the same. Besides weight, a diamond's proportions are also critical because they influence the quality of the cut, which in turn affects the diamond's overall beauty. Remember that a diamond's value is determined using all the diamond 4Cs, not just carat weight.

November 9 2021