Diamonds

KlokWurX^tm Guide to Diamond Grading - 'The 4 C's'

A diamond is categorised by what are known as the 4 C's;
- CARAT
- COLOUR
- CLARITY
- CUT.


Most people who have an interest in Diamonds and Gems have heard of the 4 C's ... but in reality that is only the start of the grading process for diamonds. There are many more factors to be taken into account when a diamond is being graded, these 'other factors' include such as - the amount of flourescence that the stone exhibits under ultra-violet light, or elements of the individual Cut such as the particular depth of the girdle, which if too thick can produce what is called 'fish-eye'. The fact that there are these other factors should be bourne in mind if you are contemplating buying a diamond as they can mean that two diamonds, which appear to the layman to have almost identical Grading Reports (the diamonds 'passport, if you like) could have very different Valuations.
The introductory guide below does not attempt to be anywhere near to a comprehensive tutorial, it is simply an overview of the standard 4-C's.
If you wish to learn more about diamonds and gems then we have suggested a number of beginners and advanced books. See our library pages, within the Trade Section for more information.

* Carat - the weight and consequent size of the diamond specified in Carats.
1 carat is divided into 100 'points' of diamond mass/weight.
1 Carat is equal to 5 grams. 1 kilogram is equal to 200 Carats

* Colour - the amount of colour (generally yellow to yellow-grey) the diamond contains, ranging on a scale from 'D' to 'Z'.
'D' being entirely colourless and the most valuable, whilst Z are quite heavily coloured.
Z+ are classed as 'fancy' and can contain some of the best and also some of the worst diamonds depending upon the actual colour and its intensity.

The categories of Colour are:-

A diamond's colour grading certainly affects its price, but it isn't the only quality you should consider before purchasing a stone, especially if it is already mounted in a ring or other setting.
Grading of diamonds is always carried out with the stone unmounted and positioned 'table down'. Therefore once a stone is mounted it can look more coloured than when it was being graded.
This means then for example that a 'near colourless' stone could appear 'very light yellow' when mounted up in a gold ring. It doesn't make the stone any less valuable but it might mean that a 'faint yellow' stone may look exactly the same in a similar ring.
Therefore if your budget won't run to allowing you to purchase a top-graded diamond it does not mean you can't still own a beautiful gem; and after all no-one but a trained gemnologist or jeweller will probably ever notice the difference, and hardly ever once it is on your finger.


* Clarity - the quality of 'clearness' or 'purity' of the diamond. These elements are graded by the trained eye using a standard 10x loupe. When describing the Clarity reference is made to the following terms
Inclusions comprising the following:-
* Imperfections, or internal flaws.
* Tiny spots of white, black, or other colors.
* Cracks. Some cause no problems at all. Other could cause the stone to split.
* Colored and uncolored crystals.
Blemishes which are:-
* Flaws on a diamond's exterior surface.
(Many exterior flaws are the result of the cutting and polishing process)
The stones are then classified as follows:
F or FL = Flawless, No inclusions or blemishes visible.
IF = Internally Flawless, No internal inclusions visible, the stone has slight external blamishes on the surface.
VVS1 & VVS2 = Very Very Small Inclusion, Extremely difficult to find under 10x magnification
VS1 & VS2 = Very Small Inclusion, Difficult to find under 10x magnification
SI1 & SI2 = Small Inclusion, Noticeable under 10x magnification. Imperfect
I1, I2 and I3 = Inclusion also called P1, P2 and P3, Flaws visible to the naked eye


* Cut - Refers to the proportions, finish, symmetry, and polish of the diamond.

The cut of a diamond, that is it's overall shape along with it's conformity to the perfect shape for it's particular style, along with its depth and width, and the uniformity of the facets, all combine to determine a diamond's brilliance.

Many gemnologists consider that the cut is the single most important diamond characteristic because, even if a diamond has perfect colour and clarity, one with a poorly performed cut, or even an incorrect choice of style will have a dulled brilliance.
In a Round Brilliant it is the width and depth which have the greatest effect on how light travels within the stone and how it then exits it in the form of the 'sparkle' (as it is commonly called) which is in reality it's brilliance.
Too Shallow a Cut, and the light is lost out of the bottom causing the diamond to lose brilliance and appear lacklustre.
Too Deep a Cut, and the light escapes out of the sides causing the diamond to appear dark and dull.

The diamond's proportions, that is the depth compared to the diameter and the diameter of the table compared to the diameter of the diamond, determine how well light will refract within the diamond. Get this wrong and the stone looses it's 'fire' and 'life'.

In 1919 a young mathematician, Marcel Tolkowsky, wrote a Masters thesis on the proportions for round brilliant cut diamonds. This became the basis for what is now known as the 'Ideal Cut'. It is said he asked passers by, in the streets of London, to select the most appealing diamond from a small group. From these casual observer opinions, together with those of the diamond cutters in his family's Belgian business, he confirmed the proportions of the best looking diamonds. He then applied math and physics to prove why. The proportions he chose produce a beautiful diamond. But it has taken more than 80 years for the industry to realize that his theorem predicted a range of proportions, not just the single set of parameters shown on the image; he was aware of a trade off between maximum brilliance and maximum fire that results from varying combinations of crown and pavilion angles.



Marcel Tolkowsky's ideal cut proportions

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An abridged Glossary of terms relating to the Cut of a Diamond:-
Diameter: The width of the diamond as measured through the girdle.
Table: The largest facet of a gemstone.
Crown: The top portion of a diamond extending from the girdle to the table.
Girdle: The narrow band around the widest part of a diamond.
Pavilion: The bottom portion of a diamond, extending from the girdle to the culet.
Culet: The facet at the tip of a gemstone. The preferred culet is not visible with the unaided eye (graded "small" or "none").
Depth: The height of a gemstone measured from the culet to the table.

The STYLE of CUT of Diamonds, and other Gemstones follows strict patterns. The following represent the most common 'Cuts' of Diamonds


Emerald - Heart - Radiant - Brilliant - Princess - Pear - Oval - Marquise