Source: GIA Website.

One of the first things most people learn about diamonds is that not all diamonds are created equal. Every diamond is unique. Diamonds come in many sizes, shapes, colours, and with various internal characteristics.

Diamond professionals use the grading system developed by GIA in the 1950s, which established the use of four important factors to describe and classify diamonds: Clarity, Colour, Cut, and Carat Weight.



Diamonds can be fashioned into a variety of shapes and still be beautiful.

These are known as the 4Cs. When used together, they describe the quality of a finished diamond. The value of a finished diamond is based on this combination.

A diamond's value is often affected by the rarity of one or more of the 4Cs. Colourless diamonds are scarce - most diamonds have tints of yellow or brown. So, a colourless diamond rates higher on the colour grading scale than a diamond that is light yellow. Value and rarity are related: In this case a colourless diamond is more rare and more valuable than one with a slight yellow colour. The same relationship between rarity and value exists for clarity, cut, and carat weight.

COLOUR
Subtle differences in colour can dramatically affect diamond value. Two diamonds of the same clarity, weight, and cut can differ in value based on colour alone. Even the slightest hint of colour can make a dramatic difference in value.



This emerald cut diamond is colourless and is a D colour grade. - Courtesy Lazare Kaplan Diamonds


In the normal colour range, the closer a diamond gets tocolourless, the higher its per-carat price. There's an especially large leap in the price of a colourless diamond, which is extremely rare.

These diamonds - graded E, K, and Z - represent diamond colours near the top, middle, and bottom of the GIA Colour Scale. - © GIA & Tino Hammid



To eliminate the guesswork from grading a diamond's colour, graders compare it to masterstones that represent known colours in the GIA D-to-Z scale. - © GIA & Tino Hammid



The GIA D-to-Z scale is the industry standard for colour-grading diamonds. Each letter represents a range of colour based on a diamond's tone and saturation.

Many diamonds emit a visible light called fluorescence when they're exposed to ultraviolet (UV) radiation. Although invisible to the human eye under the right conditions, you can see fluorescence in about 35 percent of gem diamonds.

Blue is the most common fluorescent colour in gem-quality diamonds. In rare instances, fluorescence can be white, yellow, orange, or many other colours.

Strong blue fluorescence can make a light-yellow diamond look closer to colourless in sunlight. Blue and yellow are colour opposites and tend to cancel each other out, so blue fluorescence masks the yellow colour. If the fluorescence is too strong it can make the stone look cloudy or "oily," which can lower the value of the diamond.

CLARITY
Diamonds have internal features, called inclusions, and surface irregularities, called blemishes. Clarity is the relative absence of inclusions and blemishes.

Among other things, blemishes include scratches and nicks on a diamond's surface. Inclusions are generally on the inside, and some might break the surface of the stone. Sometimes, tiny diamond or other mineral crystals are trapped inside a diamond when it forms. Depending on where they're located, they might remain after the stone has been cut and polished, and they can affect a diamond's appearance.

No two diamonds have exactly the same clarity characteristics in exactly the same locations. This fact helps gemmologists identify individual diamonds.

Like the rest of the 4Cs, clarity's influence on value is directly related to the concept of rarity. Flawless is the top grade in the GIA Clarity Grading System. Diamonds graded Flawless don't have visible inclusions or blemishes when examined under 10-power (10X) magnification by a skilled and experienced grader.



As clarity increases, and if all other value factors are equal, diamond price per carat also increases.

There are 11 clarity grades in the GIA clarity grading system. They are Flawless, Internally Flawless, two categories of Very, Very Slightly Included, two categories of Slightly Included, and three categories of Included.

The effect of a clarity characteristic on the clarity grade is based on its size, number, position, nature, and colour or relief.



The GIA clarity scale includes eleven diamond clarity grades. The scale narrows at the top because there are very few diamonds in the higher clarity grades.

A clarity characteristic's effect on a diamond's clarity grade is determined by five factors: size, number, position, nature, and color or relief. - Gary Roskin GG, FGA

Diamond professionals use a set of terms that originally included very very slightly imperfect, very slightly imperfect, slightly imperfect, and imperfect. In recent years, the term imperfect has been replaced with included. (GIA uses included in its clarity grading system.)

These terms were shortened to the initials VVS, VS, SI, and I. The abbreviations eventually gained acceptance throughout the international diamond community.

CUT
A beautifully finished diamond is dazzling, with every facet displaying the craftsman's skill and care. When a diamond interacts with light, every angle and every facet affect the amount of light returned to the eye.

In efforts to differentiate themselves, and because of increasing demand for precision in cutting, many manufacturers fashioned diamonds to exacting standards throughout the decade. Note the precise arrow pattern in this 1.54 ct diamond.



A well-cut diamond displays the beauty consumers expect to see in a diamond.

A beautiful diamond looks the way it does because of three optical effects: white light reflections called brightness, flashes of colour called fire, and areas of light and dark called scintillation. Pattern is the relative size, arrangement, and contrast of bright and dark areas that result from a diamond's internal and external reflections. There must be enough contrast between the bright and dark areas to give the pattern a crisp, sharp look.

As a general rule, the higher the cut grade, the brighter the diamond. Under fluorescent lighting, these diamonds (left to right) display high, moderate, and low brightness.

The term "cut" also can describe a fashioned diamond's shape. Shapes other than the standard round brilliant is called fancy cuts. They're sometimes called fancy shapes or fancies. Fancy shapes also have names of their own, based on their shapes. The best known are the marquise, princess, pear, oval, heart, and emerald cut.

Fancy-shape diamonds, along with the classic round diamonds, are popular choices for today's jewellery consumer. Courtesy Lazare Kaplan Diamonds

CARAT WEIGHT
There are two things that often surprise people when they start learning about diamonds and carat weight.

The first is the precision with which diamonds are weighed. Diamond weights are stated in metric carats, abbreviated "ct." One metric carat is two-tenths (0.2) of a gram - just over seven thousandths (0.007) of an ounce. One ounce contains almost 142 carats. A small paper clip weighs about a carat.

The metric carat is divided into 100 points. A point is one hundredth of a carat.

Diamonds are weighed to a thousandth (0.001) of a carat and then rounded to the nearest hundredth, or point. Fractions of a carat can mean price differences of hundreds - even thousands - of dollars, depending on diamond quality.

Over a carat, diamond weights are usually expressed in carats and decimals. A 1.03-carat stone, for example, would be described as "one point oh three carats," or "one oh three." Weights for diamonds that weigh under a carat are usually stated in points. A diamond that weighs 0.83 carat is said to weigh "eighty-three points," or called an "eighty-three pointer."

Large high-quality diamonds are rare and valuable gems. This diamond weighs a remarkable 100.20 carats and is internally flawless. - © GIA and Harold & Erica Van Pelt, courtesy The Steinmetz Group

In summary: Large diamonds are more rare than small diamonds. The scarcer something is, the more it is worth. So a larger stone doesn't just cost more. It also costs more per carat. A 1-carat diamond weighs the same as four 0.25-carat diamonds. But even if all the other quality factors are equal, the larger diamond is worth much more than the sum of the four smaller diamonds.

Carat weight can also be symbolic. While the visual difference between a 0.98-carat diamond and a 1.01-carat diamond is negligible, many people will opt for the larger stone - even at a much higher price. Some weights are considered "magic sizes": half carat, three-quarter carat, one carat, etc. There's not much difference in their weights, but if both are D-colour round brilliants with identical clarity and cut, the size makes all the difference. They really don't look much different, but if a consumer's heart is set on the one-carat size, the difference is enormous. The fact that the second stone is slightly over the "magic" one-carat size can give it as much as a 20 percent difference in price with only a 6-point difference in weight.



This oval shape diamond weighs 1.01 carats and made the 1.00 carat magic size range. When diamonds reach the so called magic sizes the value per carat increases. - Courtesy Lazare Kaplan Diamonds