Understanding diamond quality: Introduction to the 4 Cs of Diamonds
How do you determine the quality of a cut and polished diamond? The answer lies in the four ‘Cs’ developed by GIA (The Gemological Institute of America) more than 50 years ago in order to standardize the grading of diamonds. The four ‘Cs’ stand for Carat, Color, Clarity, and Cut of a stone. If you are thinking of buying a diamond, whether as a decorative jewel or an investment, these are the first criteria you’ll be looking at in order to select your own unique diamond.
Actually, there is one thing you’ll want to decide on as the very first step: the shape. Diamonds are cut in many different types of shape: among the most common are round, oval, emerald, pear and even heart, yes heart !
If you want to learn about how diamonds are cut, there is a section on this website dedicated to this highly specialized and arduous task, but for now just know that virtually any shape is possible.
Let’s get back to the 4 “Cs”:
The Carat
This can be considered the most important of the “Cs”, as it will largely decide the price of a diamond (a 1 carat diamond can easily be valued at triple the price of a 0.5 carat diamond, and so forth). The carat is the weight (not the size) of the diamond, standardized at 200mg, or 1 fifth of a gram, for 1 carat. A stone can be cut in such a way that it appears larger on the surface, although weighing the same as another, apparently smaller stone. Typically, after the shape, you will start by deciding on a carat. Just be aware that prices quickly reach exorbitant levels, for example a 3 carat diamond is in the 35,000$ to 40,000$ range.
The Color
Once the diamond is cut, a color grade is attributed to the diamond by the certifying lab (such as GIA) who has examined the stone. The grading goes from D (the best) upward toward Z (the worst).
A grade of D, E or F means the diamond is virtually colorless, but can till have minuscule traces of yellow. A diamond should be as transparent (colorless) as possible: as you can see in the image above the diamonds toward the left look much prettier and purer than those to the right. It goes without saying that the more colorless, the more expensive a gem will be. Color can be seen by experts with the naked eye (under natural, sunless daylight) or by using scientific instruments. Color is not to be confused with fluorescence (explained later), although it is thought that there exists a correlation between the two.
The Clarity
The clarity of a diamond indicates how flawless it is in its internal and external (superficial) characteristics. These are only seen with a 10x loupe, but are significant in determining the value. The diamond can have inclusions, tiny crystals and minerals embedded in the stone or feathers, small cracks within the stone. The certificate will indicate this and might even have pictures showing the slightest flaws of the diamond, seen from above and below. Ideally, you want a diamond in the VVS2 range and above. But again, the more flawless a gem is, the higher the price.
The Cut
This refers to the quality of the cutting which has been performed on the the stone, not to be confused with its shape. The grade here indicates the quality of aspects such as brightness, fire and scintillation as well as the stone’s proportions. The object is to establish how well the diamond will refract light, which decides how much “fire” and “life” it has. There are typically five cut grades: Poor, Fair, Good, Very Good and Excellent.
Fluorescence, Symmetry and Polish
Fluorescence is not part of the 4 Cs, but is nonetheless an identifying characteristic of the diamond. It is defined as the property of objects to emit visible light under certain circumstances. When a diamond is for example exposed to long-wave ultra-violet (UV) rays from the sun, it can emit a blueish light or, more rarely, a yellow or orange light. By examining the diamond under UV-light (they exist in desk versions and even portable), you will see the gem emit a certain degree of colored light, most commonly blueish. The certification report will indicate this with a grade from ‘None’ to ‘Very Strong’. It will specify for example: ‘Fluorescence: Light Blue’. Fluorescence is neither a bad or good quality, some people find that a fluorescent diamond adds charm and beauty, others do not. There is no standard opinion on the subject, it’s a matter of taste. Examine your diamond under UV-light and judge if it is to your taste or not.
Symmetry refers to the deviation or not from what is considered ‘proper symmetry’ for a diamond. Essentially, a round cut diamond for example is an upside-down triangle with a crown at the top. Several features are looked at in certifying good or bad symmetry, most importantly the crown and the culet, see figure below. Without getting too technical, unequal angles in the crown, uneven crown height, deviation of the culet and poor facet distribution, all would determine a lower grade. Grades range from ‘Poor’ to ‘Excellent’. You want your diamond to have at least a grade of ‘Very Good’ symmetry.
Polish is also graded from ‘Poor’ to ‘Excellent’. After cutting the diamond, the final stage is polishing: it is this process which determines how the diamond will look when handed to the consumer. Here the certifying authority looks for any abrasions and scars left from the polishing process. Scratches and nicks are also looked for in determining if the diamond has been perfectly polished or not. Again, you want your diamond to have a grade of ‘Very Good’ polish at least.
Triple X diamonds
A quick paragraph on triple X diamonds. This is not a term used so much by certification authorities, but among jewelers and traders this term indicates a diamond which has a certified ‘Excellent’ grade in three key areas: cut, polish and symmetry. Basically it is a diamond which is as perfect as can be expected, in proportions and appearance. However, they are also more expensive (sometimes a great deal more) than gems with lower grades. These diamonds are for the perfectionists out there, who want the very best and are willing to pay for it.
Example report with 4 “Cs”
Here below is an example of the grading of a 1,01 carat diamond, with color grade “F”, clarity grade “SI1” (Slightly Included 1) and cut grade “Excellent”. As you can see, the report is quite detailed, also specifying the shape, measurements as well as polish, symmetry and fluorescence. Also, a code is assigned to each diamond and the certifying authority will typically engrave this code on the diamond itself, making it unique and easily identifiable.
Links to more knowledge
The Gemological Institute of America (GIA)
The Diamond Pro (Diamond Prices)
Books of interest
Diamonds. (Bruton, Eric. 1978, Chilton Book Company, Pennsylvania, USA)