Understanding How Gemstones are Weighed and Measured

Although bigger seems better and more expensive, it's not always so in the world of jewelry. In fact, size isn't even synonymous with carat weight and you need to keep that in mind when shopping for gemstones.

Carat Weight versus Size

Diamonds and colored gemstones alike are evaluated and appraised according to the 4C’s which are made up by cut, color, clarity, and carat weight. Carat weight is very much different from size and definitely more important than the latter. Also, take note that carat is different from karat, which is the measurement unit used for gold. Carat weight uses the abbreviation ct and ct TW for carat total weight.

In the past, carob seeds were traditionally used to measure a gemstones weight because of its uniform shape and size. In 1913, however, the jewelry industry managed to set universal standards for measurement and the carat weight system was born.

Now, one carat is always equivalent to one-fifth or twenty percent of one gram. One carat is made up of one hundred points. As a gemstones weight goes up, so does its value or price per carat.

The way carat weight is discussed is occasionally a cause for confusion. Remember that a gemstone with .005 ct may be called a half point gemstone. A .25 ct gemstone could be called a quarter carat while a .50 carat gemstone may be referred to as a half carat or fifty points.

Gemstones are often listed according to their size because it is more uniform than carat weight. Two different gemstones may have the same size but different carat weights and consequently, different prices as well.

Factors Affecting Gemstone Carat Weight

Gemstone Material A 1 carat ruby is smaller than a 1 carat emerald. This is mainly due to the gemstones specific gravity. A gemstones denseness level can make it carry greater weight even though it has a smaller size than other gemstones with the same carat weight. While carat weight is very much important for traditional and much-prized gemstones, it tends to lose its significance when it comes to common gemstones with high supplies like blue topaz, citrine, and amethyst. Amethyst, in fact, used to be classified as one of the precious stones but its price went down when loads of shipment arrived from Brazil in the 19th century.

Gem Shape or Cut The shape and cut can occasionally affect the carat weight. While most jewelry designers cut gemstones with size and carat weight in mind, others place more importance on its aesthetic value and may therefore reduce carat weight and size in favor of improved looks. The same can be said for shape as well.

Table Diameter The table diameter is often considered important only for measuring or evaluating the brilliance of a given gemstone, but what few people realize is that it can affect the gemstones carat weight as well.

Similar to gem cut and shape, if the table diameter is shaped in such a way to maximize its window-like characteristics, carat weight might be consequently sacrificed.

Today, studies show that a lot of gemstones sold on the market are cut to take commercial concerns into consideration. Many of these gemstones report loss in weight of just 10% or lower. Some are even cut to the extent of making them appear bigger as well.

Girdle Thickness The girdle is the dividing line between a gemstones pavilion and crown or its bottom and top facets. Ideally speaking, girdles must be extremely thin and preferably visible only to the naked eye like a light line. Thick girdles not only reduce brilliance and light yield but negatively affect the gemstones color as well. Girdles are often referred to as edges and they are graded as any of the following: very thin, thin, medium, thick, thick, and very thick. Thin girdles look better, but they're lighter in weight and easier to chip.

Crown Height The crown of a gemstone refers to its upper area and positioned on top of the girdle. Acceptable crown height for gemstones is between 11.0 to 16.2% of the girdle diameter. Greater crown height often means greater carat weight.

Pavilion Bulge The pavilion is the bottom portion of a faceted gemstone. Greater bulge usually means heavier carat weight.

Culet Size This is the facet at a gemstones tip. Like the girdle, culets are better invisible to the naked eye. It may be sharp or pointed.

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Knowing the Different Cuts for Gemstones

When grading and appraising gemstones, cut may not be as influential as the other C's like color, clarity, and carat weight, but it is definitely an influencing factor when it comes to the gemstones overall beauty. To properly evaluate the cut of a given gemstone, you must not only study its face-up view or the surface or top view but study it from all other angles as well. An excellent cut can reduce loss on carat weight but enhance its looks to breathtaking proportions at the same time.

Common Cuts Used on Gemstones

Brilliant Cuts A brilliant-cut gemstone usually has three flat polished surfaces per facet. They are positioned in such a way to radiate the best light from the gemstone. Gemstone cutters also make sure that the angles will enhance the brilliance of the gemstone. Brilliant cuts are mostly used for diamonds and transparent gemstones.

Some facets will have one or more shapes like stars, hearts, kites, and lozenges. Variations of the brilliant cut include the naivet‚ or boat-shaped marquise, per-shaped pendeloque, and oval shape. Oval shapes are suitable for gemstones with lower carat weight because they can make them appear bigger.

The most popular variation of all is the full-cut round brilliant. It has fifty-eight facets, presently the greatest count for brilliant cut gemstones. The single brilliant cut, on the other hand, has seventeen to eighteen facets. For gemstones used in earrings and pendants, the briolette variation is mostly used to provide it with circular cross-section teardrop shapes. Brilliant cuts with triangular dimensions are called trilliants while square brilliant cuts are also known as princess cuts.

Step Cuts Another popular cut for a gemstone is the step or trap cut. Step cuts are best used for colored gemstones because they possess four-sided table facets and girdles as well as parallel quadrilateral facets. The term step cut was used because this gemstone cut bears similarities with a staircase. Step cuts have fewer facets than brilliant cuts.

One well-known variation of a step cut is the baguette. It is rectangular in shape but with square corners. Emerald cuts are also quite popular. Its name was derived from its consistent use with emeralds. Emerald cuts remove the corners and form an octagonal shape. Clipping off the corners protect delicate gemstones like emeralds and facilitate setting of gemstones at the same time. Other popular variations for step cuts are window, table, radiant, and oval.

The best advantage of step cuts is its ability to enhance a gemstones color, making the color richer and appearing to have originated straight form the belly of the gemstone.

Mixed Cuts Mixed cuts for gemstones are mostly combinations of brilliant and step cuts. The crown or top portion of a gemstone will resemble a brilliant cut while the pavilion or bottom portion of a gemstone will receive a step cut. At times, the two cuts will appear side by side. Mixed cuts are also characterized by their rounded outlines. Many transparent gemstones like rubies and sapphires are often cut this way. Gemstones with mixed cuts are also commonly set in prongs.

Variations for mixed cuts include but are not limited to cushion, zircut, pear or teardrop, and oval.

Cabochon Cuts A gemstone with a cabochon cut will appear rounded on top and flat on the bottom. At times, gemstones will only appear in this cut. Height of a gemstones dome with a cabochon cut varies. The name is derived from the French term used for bald heads. Cabochon cuts are simplest to make, and that's why you'll often see them used on affordable gemstones and those that will not benefit from faceting.

Fancy Cuts Any other cut besides those mentioned above is usually referred to as fancy. A checkerboard cut, for instance, will have a combination of a large table facet on top and a mixed cut. A rose cut will have a round girdle outline, flat base, dome-shaped crown, and facets of a brilliant cut.

When judging the cut of a gemstone, start by evaluating it face up. See if the gemstone shows uniform color distribution and radiates light in the best possible way. Gemstones cut with large windows are unappealing. Lastly, recheck all other angles and determine if the cut took both carat weight and looks into consideration.

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