Grading Diamonds and the 4 C’s
Diamond Grading Information and Terminology.
The value of a diamond is determined by the quality elements often referred to as the “4C’s”. Clarity, Colour, Cut and Carat Weight combine in this assessment in order that the value of stone any given diamond can be judged. The higher a level a diamond is in these things the more costly it is likely to be. Clarity is often assumed to be the most important of the 4 C’s after carat weight, but in fact colour and cut can have a more profound visual effect on the appearance of a diamond. It is for this reason that Excellent cut is the most highly sort. It should be noted that the best diamond for a client, generally will have a balance of all things, not necessarily be in the very top of each area of the grading standards.
Carat is the unit of weight for all gemstones. The word “carat” originates from the seed of the carob tree pod (which is found in tropical climates). These seeds were historically used by merchants to balance scales to weigh precious gems.
One carat is subdivided into 100 “points”. Therefore a diamond measuring 75 points is 3/4 carat in weight, or 0.75 ct.
A diamond’s clarity is determined by the number, nature, position, size and colour of internal characteristics called “inclusions” and surface features called “externals”. These irregularities occurred in the liquid magma (volcanic rock) within which the diamond was created. Diamonds are mostly pure carbon, however, as they crystallise, other minerals nearby, or other particles of carbon forming at a different rate may have become trapped within the cooling mass. These show themselves as the various characteristics which make up the clarity of a diamond (included crystals, feathers, clouds etc.)
Clarity is measured on a scale ranging from flawless, (Fl) to heavily included (P3.) The clarity of a diamond is graded by using a 10 X magnification jewellers loupe, under good lighting by an experienced grader/valuer. The final clarity grade is determined by how visible any inclusions or externals are.
This diamond shows many of the issues and inclusions in the following text , and is commonly found in low end retail stores It is well below the Ellissi recommended standards.
Below is an illustration of the typical size and position of the likely inclusions a diamond may have in order to gain a particular clarity grading. It should be noted that inclusions are naturally occurring, and all diamonds are different. In order to display the inclusions, they are shown in red, however in reality they will be more clear / white or black / gray in appearance.
The highest grade of diamond has no colour at all. Increasing degrees of overall colour or tinting are measured on a scale ranging from no colour at all (D) to significantly coloured (L). A, B and C are not used in diamond grading, as before an internationally recognised system was established, these letters were already used to grade coloured gems (sapphires, rubies etc.). So as not to confuse the two systems, diamond grading colour starts at “D”. Beyond “L” is the range where the diamond’s colour is vivid and rich, called “fancy colours”. Diamonds of known colour are used as comparison stones for colour grading. Grading is done by comparing the diamond to be graded against these “master stones” under special light.
Cut, sometimes the forgotten “C”. A good or fine cut (sometimes referred to as “make”) ensures that a given stone has maximum brilliance and sparkle. This is often compromised when the stone is cut purely for weight and size alone.
One of the most important features in a diamond’s cut is the angle of the facets in the lower pavilion (the portion of the stone below the girdle). This determines the angle at which light is reflected back to your eye. This gives the stone its sparkle and play of rainbow colours. If a stone has been cut to maximise this effect then an excellent display of colours can be seen within the stone. Some stones may have been cut with more of an emphasis towards size and weight. This is not always a good thing as changing the proportions will cause light to be dispersed in directions other than back to the eye, resulting in duller looking stones. They may still be graded as VS and colour E etc. as this poor cut has no effect on the colour and clarity grading.
Cut related Terms
The best cut diamonds reflect light back to the eye evenly in the “face up” position (when looking through the top of the diamond) as would normally be the case when the stone is set into a ring mount. When a diamond is well cut, light enters through the table and travels to the pavilion where it reflects from one side of the diamond to the other intensifying in the mirror-like facets before reflecting back out of the diamond through the table and into the observer’s eye. The brightness of a stone has a profound effect on how it appears to the naked eye and is referred to as brilliance.
Polish is defined as any imperfection on the surface of the stone after the final polish by the diamond cutter. It does not affect clarity.
Table is the largest and topmost facet on the diamond’s crown. The table percentage is the value which represents how the diameter of the table facet compares to the diameter of the entire diamond. So, for example, a diamond with a 53% table has a table which is 53% as wide as the diamond’s outline. For a round diamond, gemologists calculate table percentage by dividing the diameter of the table, which is measured in millimeters by the average girdle diameter. For a fancy shape diamond, table percentage is calculated by dividing the width of the table, at the widest part of the diamond, by the millimeter width of the entire stone. The Table measurements are subtleties which vary ever so slightly and should not become a preoccupation in diamond selection.
The Pavilion is the part of the diamond that lays just below the the girdle. It is easy to see why people often neglect to consider its contribution to a diamond’s beauty. When a diamond is set, typically only the crown stands out prominently, and the girdle and pavilion are hidden beneath claws or bezels. They seem to serve only as the base, providing a way to seat the diamond in the mount. However, it is this hidden part of the diamond that is the key to brilliance. The secret is in the pavilion angles, which, in a round diamond, should typically be between 40.5 and 41.5 degrees. Light reflected back to the eye from the pavilion differs from point to point within any given diamond, this is responsible for the diamond’s brilliance. Fancy shapes such as heart or princess cuts may require deeper pavilions than round diamonds in order to achieve the same amount of brilliance.
Clarity Related Terms;
Externals, if present, occur on the surface of a diamond and are the result of the environment the diamond has been exposed to either naturally or during the mining or cutting process.
When an inclusion is near the surface an extra facet may be cut to eliminate it. This may raise the overall quality and clarity grade of the stone. In most cases they are difficult to detect with the naked eye.
This is a small part of the original rough diamond’s surface, typically around the girdle, which is left on the polished diamond.
This is a naturally occurring characteristic formed while the diamond crystal grows. It does not necessarily occur on the diamond’s surface, it is part of the stone’s structure and cannot be removed from the diamond without re-cutting the stone.
Inclusions are characteristics that occur within the diamond itself. Almost all internal inclusions are naturally occurring.
Here are some of the most common:
These are very minute crystals of other minerals or materials that were absorbed while the diamond was growing. Some are transparent and some have colour, depending on what type of crystals they are. Under a microscope they often look like little round bubbles. In the higher grades they are undetectable to the naked eye.
These are included crystals that are so minute that, even when magnified to 10X, they still only look like little dots. They can sometimes be difficult to find.
These look like extremely slender tiny needles even under microscope. They are inclusions that have caused the crystal to falter in the direction of the grain.
A natural is an included diamond crystal that reaches from the inside to the surface of the polished diamond.
Chips are usually a small, very shallow opening on the surface of the diamond. This could be a naturally occurring opening in the diamond or the result of damage the stone has received.
This is a larger version of a chip. These are sometimes created by the person doing the cutting when an included crystal near the surface of the rough diamond is removed. This may leave a cavity behind.
Feathers are small features within a diamond. Stress has usually caused this during the formation of the diamond. They can occur inside the diamond or at the surface. The term ”feather” comes from the fact that, under magnification, these features often seem to have an distinct, feathery shape to them.
Internal graining is a naturally occurring phenomenon in some diamonds. This usually occurs within the diamond’s internal structure, extremely fine lines may be seen under magnification.
Clouds are actually a cluster or a number of extremely tiny inclusions that are too small to be distinguishable from one another. This characteristic may give that area of stone a clouded appearance.
Buying the best stone that you can:
No two diamonds are the same. The size, shape, colour and location of any inclusion are all factors determining which clarity field a stone falls into. Often there is not a distinct difference between diamonds at the upper end of one grade and the lower end of the grade above. When these stones are valued after being set into jewellery it can be difficult for even the trained eye to tell which grade the diamond may actually be. This can be due to reflections of the metal surrounding the stone, for example, it could look slightly more yellow if set in a yellow gold setting. An inclusion may be hidden under a claw or part of the metal rim around the stone (referred to as the bezel) and as such may have been valued higher (a jewellery valuer can only value what he or she can see, not what may or may not be obscured from view).
As a result, comparing diamonds from shop to shop in ready made rings based on colour and clarity alone may not tell the whole story. Even buying a certified diamond of D colour and VVS clarity does not guarantee a good appearance and play of light within the stone. If the cut is poor, a lower grade stone with better cut will often look better. Differences between individual stones can be explained fully when purchasing diamond from Ellissi and the style of ring is tailor made by us, to suit the diamond you choose.
Grading of diamonds requires great expertise, to the untrained eye stones which may be 3 or 4 grades apart may not appear to differ. A quality diamond does not just mean a big stone – size is not everything. This is one of the main reasons new diamond purchasers find shopping and comparing jewellery prices difficult.
The solution is to buy from someone you trust who has a direct interest in the integrity of their business. Sales staff in retail shops are all too often under -trained, working in casual positions, trying to sell ready made stock they know little or nothing about.
We always recommend that you buy the best looking diamond you can afford, as you will ( in the case of an engagement ring ) be wearing the jewellery almost every day and you have to be happy with what you see.
The technical aspects of a diamond, whilst important, should not be used as the sole determining factor. How your new jewellery looks while you are wearing it should be viewed with equal importance. For more information or if you have any questions, please don’t hesitate to contact us.