Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)

Just as a dollar is divided into 100 cents, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a hundredth of a carat. Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)

The carat, the standard unit of weight for diamonds and other gemstones, takes its name from the carob seed. Because these small seeds had a fairly uniform weight, early gem traders used them as counterweights in their balance scales. The modern metric carat, equal to 0.2 grams, was adopted by the United States in 1913 and other countries soon after. Today, a carat weighs exactly the same in every corner of the world.

Cut is the factor that fuels a diamond’s fire, sparkle and brilliance.

The traditional 58 facets in a round brilliant diamond, each precisely cut and defined, are as small as two millimeters in diameter. But without this precision, a diamond wouldn’t be nearly as beautiful. The allure of a particular diamond depends more on cut than anything else.

Though extremely difficult to analyze or quantify, the cut of any diamond has three attributes: brilliance (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the pattern of light and dark areas and the flashes of light, or sparkle, when a diamond is moved).

People often think of diamond cut as shape. Round is the shape used in most diamond jewelry. All other shapes are known as fancy shapes. Traditional fancy shapes include the marquise, pear, oval and rectangle. Hearts, triangles and a variety of others are also gaining popularity in diamond jewelry.

As a value factor, though, cut refers to a diamond’s proportions, symmetry and polish. For example, look at a side view of the standard round brilliant. The major components, from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion that’s known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth. A wide range of proportion combinations are possible, and these ultimately affect the stone’s interaction with light.

In early 2005, GIA unveiled a diamond cut grading system for standard round brilliants in the D-to-Z color range. This system, the product of years of intensive research and testing, assigns an overall diamond cut grade ranging from Excellent to Poor.

The distance from the bottom of the girdle to the culet is the pavilion depth. A pavilion depth that’s too shallow or too deep will allow light to escape through the sides or the bottom of the stone. A well-cut diamond will direct more light through the crown.

Diamond color is all about what you can’t see. Diamonds are valued by how closely they approach colorlessness – the less color, the higher their value. (The exception to this is fancy color diamonds, such as pinks and blues, which lie outside this color range.) Most diamonds found in jewelry stores run from colorless to near-colorless, with slight hints of yellow or brown.

GIA’s color-grading scale for diamonds is the industry standard. The scale begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or light yellow or brown. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

Many of these color distinctions are so subtle as to be invisible to the untrained eye. But these slight differences make a very big difference in diamond quality and price.

Before GIA developed the D-Z Color Grading Scale, a variety of other systems were loosely applied. These included letters of the alphabet (A, B and C, with multiple A’s for the best stones), Arabic (0, 1, 2, 3) and Roman (I, II, III) numerals, and descriptions such as “gem blue” or “blue white.” The result of all these grading systems was inconsistency and inaccuracy. Because the creators of the GIA Color Scale wanted to start fresh, without any association with earlier systems, they chose to start with the letter D—a letter grade normally not associated with top quality.

Because diamonds formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes).

Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds without these birthmarks are rare, and rarity affects a diamond’s value. Using the GIA International Diamond Grading System™, diamonds are assigned a clarity grade that ranges from flawless (FL) to diamonds with obvious inclusions (I3).

Every diamond is unique. None is absolutely perfect under 10× magnification, though some come close. Known as Flawless diamonds, these are exceptionally rare. Most jewelers have never even seen one.

The GIA Clarity Scale contains 11 grades, with most diamonds falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity grade, the GIA system considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10× magnification.

  • Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
  • Internally Flawless (IF) - No inclusions and only blemishes are visible to a skilled grader using 10× magnification
  • Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
  • Very Slightly Included (VS1 and VS2) - Inclusions are minor and range from difficult to somewhat easy for a skilled grader to see under 10x magnification
  • Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader under 10x magnification
  • Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance

Like the color scale, GIA’s clarity grading system developed because jewelers were using terms that were easily misinterpreted, such as "loupe clean," or "piqué." Today, even if you buy a diamond in another part of the world, the jeweler will likely use terms such as VVS1 or SI2, even if her language is French or Japanese instead of English.

Also known as the Square Emerald Cut, the Asscher Cut was initially developed by Joseph Asscher in 1902 and gained popularity in the Art-Deco movement following World War I

Asscher stones maintain a classic appearance with a better balance of scintillation than the emerald cut which they resemble. Over the last decade, the Asscher cut diamonds have gained popularity in bridal media, which could be attributed to a redesign of the diamond.

After realising that the Asscher cut was still popular, Edward Asscher (grandson of Joseph Asscher) returned to the Netherlands with the idea to craft a new, more dynamic species of Asscher cut diamonds with more brilliance and shine than before. The Royal Asscher cut diamond boasts 16 more facets than the original Asscher cut’s 58 allowing the diamond to catch light much better.

Asscher cuts can vary slightly in cut, proportions and angles as the cutter of the diamond decides the ultimate details of their rendition of the cut. However, the Royal Asscher boasts an international patent, which means that not only does the Royal Asscher Company have exclusive rights to cut a Royal Asscher stone, but may also limit the range of angles that can be used to shape the diamond.

As its name suggests, a cushion cut is a square or rectangular shape with rounded corners that resemble a pillow. The cushion cut is usually comprised of 58 facets with a typical ratio of 1.00 to 1.05 for square shapes and 1.10 or greater for more rectangular ones. Although not as brilliant as round brilliants, cushion cuts have large facets allowing for a greater separation of white light into spectral colors.

The cushion, pillow or candlelight cut was developed in the 19th century and has undergone several transformations and developments since. The cut has greatly benefited from the invention of cleaving as this process has helped to maximize the shape’s light dispersion making it more dynamic and brilliant.

The cushion cut may be described as a cross between the old mine cut and modern oval shape. As techniques and cutting styles have evolved over the years, several variations of the cushion cut have been developed, such as the Cushion Modified Brilliant*which may have an extra row of facets on the pavilion that alter the look of the diamond.

These modified brilliants often have what is called the“sparkling water” or “crushed ice” effect, giving them greater scintillation.Other subtle alterations have also been introduced, such as adding symmetricalkite- or half-moon-shaped facets to the pavilion and below the girdle.

The understated elegance of an emerald cut diamond is admired by many. Although not a traditional engagement ring, non-traditional engagement rings seem to be very popular these days. The emerald cut is essentially a step-cut diamond and the most popular in this category. The cut has four longer sides are made up of bevelled corners with two, three or four concentric rows of facets, parallel to the girdle on the crown and pavilion.

Due to the long step cuts, emerald cut diamonds do not hide imperfections well. In lower clarity emerald cuts, inclusions become very obvious. This cut may have 49 facets or more, and yet, are less scintillating due to the step cut style of faceting. Since lots of scintillation masks inferior colour, this type of facet pattern may emphasize inferior colour.

When shopping for an emerald cut, be sure to choose the highest quality stone within your budget.

A beautiful shape of love and romance, this cut requires a skilled cutter. This romantic and feminine shape may not be as common as might expect, which is what makes it so special. Heart shaped diamonds should have two symmetrical halves with a distinct cleft and even wings and lobes. This cut is perfectly suited to Valentine’s Day.

Named after a mistress of Louis XV in the year 1745, this long and narrow shape is said to resemble the shape of Marquise de Pompadour’s mouth. The long and narrow shape creates and illusion of the diamond being larger in size. Symmetry is crucial with this shape since even the slightest difference in proportions can create an uneven and imbalanced look.

This brilliant cut diamond looks stunning when set with round or pear shaped side stones. The length of the Marquise tends to make fingers appear long and slender.

With a typical ratio between 1.33 and 1.66, the oval cut creates a bow-tie effect when light passes through the diamond. The central facets of the stone appear shadowed when this happens. Altering the depth of the pavilion and adjusting the angles of the table and facets causes light to diffuse in the central area.

Ratio is a crucial aspect to this shape as it may have a significant effect on both the light dispersion from within the stone and the appearance of the finger. When considering this shape, bear in mind that a longer shape with elongate the finger, while a rounded shape will help curb the bow-tie effect.

This unique hybrid diamond cut combines the brilliance and design style of the Round Brilliant and the curvature of the Marquise Cut. As a result, we receive a diamond shape with a single point and rounded end.

Usually made up of 58 facets, the number of pavilion facets may vary from 4 to 8. Pear shaped diamonds tend to vary in appearance with some having “high shoulders” making the stones appear more angular.

Similar to the Marquise and Oval cuts, the pear shape may also suffer from the fearsome “bow-tie effect” wherein light passing through the stone casts a shadow across its central facets. This may be counteracted by modifying the angles of the tables and facets to better diffuse light in the central area.

Precursors of the princess cut include the Barion created by South African cutter Basit Watermeyer and the Quadrillion – a similar cut with only 49 facets. After several years of optical research, the modern Princess cut was created in the form of a square stone made up of 58 facets.

The square version of the round brilliant cut, The Princess cut is usually made up of 57 or 76 facets with a general ratio of 1.0 to 1.05. Its four bevelled sides resulting from its pyramidal shape disperses more light than any other square shaped diamond. This makes it a popular choice for both solitaire engagement rings and earrings.

A unique hybrid cut, the Radiant is comprised of 70 facets and distinctly trimmed edges. Its versatile design is an amalgamation of the brilliance and depth of the round, Emerald and Princess cuts making it an extremely popular choice for jewellery.

The Radiant cut can disperse more light through the stone as a result of its extra facets. This makes it one of the most brilliant of all square and rectangular shaped stones. A hybrid featuring both brilliant and step-cuts, the Radiant cut is perfect for someone who wants all the features of the best diamond cuts.

Arguably the most popular cut, the round cut diamonds are frequently used in earrings, pendants and solitaire engagement rings. Almost all round diamonds are brilliant-cut as the angles help greatly enhance its fire and brilliance.

This cut has evolved greatly over the last century as diamond cutters have extensively researched and applied precise mathematical calculations to greatly enhance its fire and brilliance. As the most researched shape, it is possible to get the fire and brilliance you desire whilst balancing the cut, clarity and colour to suit your needs.

The origins of this cut can be traced all the way back to the mid 16th century when diamond cutters began to refine their methods by introducing more complex means of cutting diamonds. The early brilliants were known as Mazarins, which through gradual transformation and development led to the birth of the Portuguese Peruzzi or “old European cut” in the 17th century. The modern round brilliant was only created in 1919 and at the time was known as the Tolkowsky named after its creator, Russian mathematician Marcel Tolkowsky.

This cut was first developed in Amsterdam, although the design varied considerably based on the rough form of the stone. The year 1962 saw the Henry Meyer Diamond Company of New York design and trademark the modern Trillion cut and over time the trillion became the generic name for all triangular brilliant cut diamonds.

A triangular shape, comprised of three equal sides made up of 31 of 50 facets depending on whether the diamonds are used as solitaires or accent stones.

Solitaire stones are convex whereas accent stones are cut concave. Trillion cut diamonds are usually used as side stones to compliment larger solitaire stones in engagement rings although they also make for a perfect solitaire stone themselves considering their unparalleled brilliance and fire.

The brightness and sparkle of a diamond are what will draw you to the jewellery store and are what will keep you captivated long after you’ve made your purchase. Maximum brightness and sparkle are the result of excellent cutting technique, which is reflected in the diamond’s cut grade. Of the 4 C’s Cut is by far the most important as it has the most impact on a diamond’s appearance.

The ‘cut’ of the diamond is often misinterpreted as its shape rather than its cut quality. Cut is all about the diamond’s fire, sparkle, brightness and as a factor that adds value, refers to a diamond’s proportions, symmetry and polish.

Although no single proportion measurement is an indicator of what the diamond’s cut grade will range from Excellent, Very Good, Good, Fair or Poor, a number of complex factors are considered when deciding on a cut grade. While every individual facet matters in deciding the cut grade, the appearance of the diamond is a result of a combination of all its proportions.

Table size: The horizontal facet at the top of a diamond is called the table. The average table size is expressed as a percentage of the diamond’s average girdle diameter. An ‘Excellent’ grade diamond will have a table size between 52 and 62 percent.

Total Depth refers to the diamond’s depth from the surface of the table to the culet.

The Pavilion is the lower portion from the bottom edge of the girdle to the culet. Expressed as a percentage of the average girdle diameter, a Pavilion Depth that’s too deep or too shallow will allow light to escape from the side or bottom of the stone. A well cut diamond tends to direct more light upwards through the crown.

As this dimension relates to the diamond’s brightness, Pavilion Angle is a very important aspect. It is the average of the angles formed by the stone’s pavilion main facets and girdle plane. In order to be graded ‘Excellent’ the Pavilion Angle should be between 40.6 & 41.8 degrees along with other parameters being in their proper ranges.

Crown Height: From the girdle’s top edge to the table lies the crown of the diamond. The average crown height is generally expressed as a percentage of the average girdle diameter. It may affect both, the dispersion and brightness of a diamond.

Crown Angle: The angle that is formed where the bezel facets meet the girdle plane. The Crown Angle has a significant effect on the face up appearance of a round-brilliant diamond such as the one in the picture. Apart from offering contrasting routes for entering light, the best crown angles also provide a route for exiting light dispersion.

Girdle Thickness: The middle portion of the diamond which separates the crown from the pavilion is known as the girdle. The girdle serves as the diamond’s setting edge. The girdle thickness refers to the range from its thinnest to its thickest area. A medium to slightly thick girdle is usually recommended as a thick girdle adds unnecessary weight to the stone making the diamond appear smaller. In contrast, a very thin girdle, occasionally referred to as a knife edge results in a diamond that is extremely fragile and prone to chipping.

Lower Girdle/ Half Facet Length: This ratio is calculated by measuring how long the lower girdle facets are, relative to the length of its pavilion. Diamonds with longer half facets will tend to have higher scintillation.

Culet: The small facet located at the bottom of the diamond to prevent it from chipping and abrasion is called the Culet. Sizes vary from none, very small, small, medium, slightly large, large, very large and extremely large. When the culet is absent, it is referred to as a pointed culet.

Source: Gemological Institute of America

You may have come across the term fluorescence on a diamond grading report from the GIA, SGL or any other grading authority. Most people who purchase diamonds may not care about fluorescence, but if you’re one of the few who is confused by the term, it simply refers to the effects diamonds display under ultraviolet light.

In the simplest terms, diamond fluorescence is the effect that UV light has on a diamond. Similar to how whites get brighter and your teeth appear to glow, a diamond emits a visible fluorescent light when it is exposed to UV light.

Based on information collected by the Gemological Institute of America, “the strength of fluorescence has no widely noticeable effect on appearance. In the GIA Fluorescence Study, it was found that the average person could not make a distinction between a diamond with fluorescence and a diamond without”

Often observers prefer the appearance of diamonds that possess medium to strong fluorescence. Very rarely do some diamonds with extremely strong fluorescence appear hazy or oily.

Fluorescence has no effect on the structural integrity of the diamond. However, the preference to buy one that exhibits fluorescence is a personal one since the diamond’s appearance should be taken as a whole.

Source: GIA