The 4Cs of Diamond Quality

Various characteristics are graded and categorized by the diamond industry. To learn about diamonds is to first learn about the “4Cs” of gem stones.

These 4 characteristics are considered the most important in determining a diamond’s value.



Cut

The Cut, the only element of the 4Cs influenced by the human hand, is most probably the most important, and most challenging, of the 4Cs to understand. The brilliance of a diamond depends highly on its cut. A diamond's cut refers to the quality of the tiny surfaces, or facets.

A well-cut diamond reflects light internally from one mirror-like facet to another and disperses it through the top of the gem. The facets, known as the crown, culet, table, girdle and pavilion, are arranged with precise, mathematical proportions to maximise a diamond's fire, life and brilliance.

A diamond that has been well cut may be given a higher quality or value than one that is larger or of a better colour. A diamond with perfect colour and clarity could nevertheless have poor brilliance if it is not well cut.

After cutting, the size of the stone may reduce by half but its market value may increase more than four time for its brilliance and sparkle. Diamonds have a unique ability to manipulate light efficiently. This exceptional ability can be revealed and maximized only by cutting and polishing the diamond to an extremely high level of accuracy.


Carat

Carat is a measure of weight, not size. One carat is equal to 200 milligrams. The term is derived from the word ‘carob’.

Carob seeds were used as a reference for diamond weight in the ancient world. Because larger diamonds are rare, they are more valuable than the equivalent weight in several smaller diamonds.

Each carat can be subdivided into 100 “points”. This allows very precise measurements to the hundredth decimal place. A jeweller may describe the weight of a diamond below one carat by its ‘points’ alone. For instance, the jeweller may refer to a diamond that weighs 0.25 carats as a “twenty-five pointer.” Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as “one point oh eight carats.”

A one carat diamond will generally cost more than two half-carat diamonds, assuming all other qualities are equal.


Colour

Diamond colour actually means lack of colour. The diamond colour evaluation of most gem-quality diamonds is based on the absence of colour. Colour is a result of the composition of the diamond, and it never changes over time. 

A chemical pure and structurally perfect diamond has no hue, like a drop of pure water, and consequently, a higher value. Because a colourless diamond, like a clear window, allows more light to pass through it than a coloured diamond, colourless diamonds emit more sparkle and fire. The formation process of a diamond ensures that only a few, rare diamonds are truly colourless. Thus, the whiter a diamond's colour, the greater its value.

White or colourless diamonds actually occur in a range of shades – from truly colourless to off-white.  The internationally recognized GIA (Gemological Institute of America) grading system uses letter symbols from D (colourless) to Z for colour denomination.

The differences between one shade and the next are very subtle, so grading is done under controlled lighting, using a master diamond sample set for comparison and accuracy.

Natural diamonds also occur in shades of blue, green, yellow-orange, pink, red and even black. Known as “coloured fancies”, these gems are extremely rare and valuable. They are graded according to the intensity of their colour.


Clarity

Because natural diamonds are created under an incredible amount of pressure and not grown in a laboratory, it's no surprise that most diamonds have flaws.

Clarity is the degree of absence (or presence) and the visual appearance of internal characteristics called inclusions, and surface defects called blemishes.

Inclusions are flaws such as air bubbles, cracks, and non-diamond minerals found within the diamond. Inclusions are naturally occurring features formed deep within the diamond when it was crated. Blemishes are scratches, pits, and chips (some blemishes occur during the cutting process, most often at the girdle). 

Evaluating diamond clarity involves determining the number, size, relief, nature, and position of these characteristics, as well as how these affect the overall appearance of the stone. While no diamond is perfectly pure, the closer it comes, the higher its value.

Though usually invisible to the naked eye, they can influence the way light is reflected and refracted. A gemmologist will examine a diamond under 10x magnification before assigning a clarity grade from F (Flawless) to I (Included). The grade may also indicate whether the inclusion is near the centre of the stone or along its girdle, or outer edge.

While the presence of these clarity characteristics do lower the clarity grade of a diamond, they can also be viewed as proof of a diamond's identity.

GIA certificates include what is known as a "plot" of a diamond's inclusions — think of it as a "diamond fingerprint." Since no two diamonds are exactly the same, comparing the uniqueness of your diamond's clarity characteristics with the plot provided on the diamond certificate offers assurance that the diamond you pay for is the same diamond you receive.

Because they are less common, diamonds with no or few inclusions and blemishes are more highly valued and priced.