The Four Cs: Cut, Carat, Colour & Clarity
As a general principle, diamonds may feature a wide range of differing characteristics. A cursory inspection of two diamonds of the same size might indicate that they were both of equal value. However, this is not quite true; even slight discrepancies may result in significant differences in the effect, and particularly in the value, of a diamond.
Diamonds are classified in terms of quality and value by applying a set of criteria known as the Four Cs, which stand for Carat, Clarity, Colour and Cut.
CARAT (carat weight of a diamond)
A carat is the unit used to measure the weight of a diamond. One carat weighs 0.2 of a gram and is equal to 100 points. A 50-point diamond thus has a weight of 0.5 carats or 0.1 gram. Please note that the carat is a unit of weight, not of size. Thus, although a two-carat diamond weighs twice as much as a one-carat diamond it is not twice as large.
We have assembled a chart showing some popular diamond cuts in a range of carats, to give you an impression of the approximate size of the diamonds.
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The number of carats of a diamond is not a direct indication of its size. Two further factors are required to determine this:
- Dimensions of the diamond in millimetres
- Quality of the cut, i.e. execution and proportions of the cut
As a diamond set in a piece of jewellery is generally viewed directly from above, the dimensions of the crown (top part) are particularly critical in creating a visually enlarged effect. The size of the stone can also be visually enhanced by an optimum cut. The better the cut, the higher the brilliance and fire of the diamond. A diamond may appear larger when it is cut to reflect light the most effectively. The proportions of the cut are also important. A poorer-quality cut which 'hides' more weight in the lower (and thus less visible) part of the diamond, known as the pavilion, can cause the diamond to appear smaller than a well-cut stone with the same number of carats. Please also note that a diamond set in a ring may appear larger or smaller depending on the size of the wearer's finger. The slimmer the finger, the larger the diamond appears to be.
The higher the carat of a diamond, the higher in weight, larger and thus more expensive the stone. If you have a limited budget available for your diamond purchase, we recommend that you set priorities in advance. What is the most important feature for you? The size of the diamond, its cut, colour or clarity? If size is the main priority, you may be able to select a larger stone by taking advantage of minor imperfections in clarity, colour and cut.
Clarity describes the visual appearance of a diamond. Diamonds that are completely ‘flawless’, or absolutely clear under ten-power magnification, are rare. The majority contain foreign bodies or flaws in the crystal known as ‘inclusions’ which impair the clarity. These inclusions may be mineral crystals (of the same kind, such as diamond crystals within a diamond, or other minerals such as zirconia in a sapphire), natural fractures or growth features. Inclusions block or impair the direct passage of light through the stone. The smaller and fewer the inclusions in a diamond, the higher its value and clarity. Flawless diamonds are cut diamonds which show no visible inclusions under ten-power magnification. Diamond clarity is classified according to the following universally applicable scale (from IF to P3):
Although diamonds can be found in all colours, yellow tints are the most common and are graded under the same system as colourless diamonds. As a general principle, the more colourless a diamond is, the higher its value. White light passes easily through a completely colourless diamond and is refracted in rainbow colours.
Diamonds in rare ‘fancy colours’ (green, red, blue, purple, brown, yellow and black) have a separate grading system and may be more valuable or more expensive than pure white diamonds, depending on their hue (colour) and saturation (intensity). Fancy coloured diamonds are the result either of impurities in the diamond, or of irregular pressure to which the gem was subjected during its formation. Statistically speaking, only one in 100,000 diamonds is a fancy diamond.
Different laboratories use different grading terms. Here is an overview of the most common:
The most colourless blue-white diamonds are described as 'river', 'exceptional white' or 'finest white', and are classified into the categories D and E. They are followed by 'fine white' / 'rare white' (Top Wesselton) in categories F and G. Wesselton (white) is the term given to category H diamonds.
To the eye of a practised specialist, diamonds of categories D to H appear colourless when viewed through the table (the flat top of the gem). Diamonds with a yellow tint are at the bottom of the colour scale (Z) and are correspondingly lower in value.
Cutting is the name given to the process of cutting and polishing which gives diamonds their specific type and shape, enhancing their brilliance and bringing out the visual effects inherent to the stone. A well-cut or faceted diamond of any shape returns and refracts the light more effectively (scintillation). Cutting increases the brilliance of the stone and gives it the 'fire' that makes it so desirable.
If the cut is excessively deep and pointed, light will 'leak' through the pavilion (the lower part of the gem). A cut that is too flat will refract light from the top (or crown) back into the interior of the stone, where it likewise 'leaks' through the pavilion. When the proportions are correct, light is reflected from facet to facet and then returned upwards through the crown.
Whatever their type, all diamonds have only a small number of optimum cutting planes, and only a few optimum cutting directions for each cutting plane. All diamonds, regardless of their shape, have an octahedral crystalline structure.
In addition, every uncut diamond, regardless of its shape or appearance, has four three-point, six two-point and three four-point cutting planes, giving a total of 4 x 3 + 6 x 2 + 3 x 4 = 36 'soft' cutting directions for every diamond. All other cutting directions – a total of approximately 100,000 (360 x 360) – are hard. At deviations of only a few degrees from the cutting direction, the hardness of the diamond increases to the extent that it is almost impossible to cut.
A good cut is judged on the following criteria:
- Number of facets
- Thickness of girdle and culet
- Distribution of facets on the crown and pavilion of the diamond
- Percentage value of diamond's overall height (overall height divided by diameter)
- Symmetry and size of arrangement of facets
- Angle of facets to girdle plane
- Proportions of table to girdle plane
- Ratio of crown to pavilion and table height to crown height
The brilliant cut is ideal as it brings out the highest possible brilliance and colour refraction and enables the cut and polished diamond to sparkle with the maximum fire.
The brilliance of a diamond is determined by the 'finish', i.e. the quality of the cut and its proportions. The commonest grades of finish are:
- Excellent (≙ ideal)
Excellent brillance, free from marks; best proportions and symmetry; all light that enters the diamond is fully reflected; a very rare and exquisite cut
- Very Good
Very good brillance; no or barely visible external marks; very good proportions and symmetry
Good brillance, some external marks, Proportions show slight deviations from true, facets have good symmetry
Slightly impaired brillance; some large external marks; proportions and symmetry show deviations from true
The round brilliant-cut diamond (usually with 58 facets) is by far the most sought-after and also the most intensively researched diamond shape available today. Numerous theories about light behaviour and mathematical calculations have been proposed, all with the same objective: to optimise the brillance, and therefore the fire, of a round diamond.
A round diamond will typically provide more flexibility of choice in cut, colour and clarity while retaining the fire and brilliance of the stone. For maximum brilliance select a round diamond with a cut grade of Ideal or Very Good and outstanding symmetry and polish.
Besides the round brilliant cut, the princess cut is one of the most popular diamond cuts. Its brilliance and unique cut make it a favourite for engagement rings. The princess cut is also popular with men, particularly as ear jewellery. Although the princess cut is traditionally square in shape, a rectangular shape has also become popular in recent times. The special feature of the cut is its sharply angled and exposed corners, which must be taken into account when choosing the colour grade. In oder to avoid a potentially slight yellowish tint at the corners, the colour grade selected should be at least a Wesselton grade (Grade H). The length-width ratio is also important. The dimensions of square or rectangular princess-cut diamonds can vary greatly. A square princess diamond should have a length-to-width ratio of between 1 and 1.05, while a rectangular princess may have a length-to-width ratio greater than 1.10.
When viewed from the top, the emerald cut is very similar to the princess cut. However, the cut of the pavilion (lower part of the diamond) is very different. The large open table and rectangular facets of this cut highlight the clarity of a diamond; accordingly you should choose a clarity grade of at least VSI (VS1 or VS2). In addition, like the princess cut, the proportions of emerald-cut diamonds can vary widely. For the classic emerald-cut shape, the length-to-width ratio should be between 1.30 and 1.40.
The Asscher-cut diamond is visually almost identical to the emerald cut, except that it is always square in shape. Here too, a higher clarity grade should be chosen as this shape also highlights the clarity of the diamond. Furthermore, please note that slight yellowish tints at the corners may be apparent in colour grades of J and downwards.
The brilliance of oval-cut diamonds is approximately similar to that of round diamonds. This cut accentuates long, slender fingers. As with the princess and emerald cuts, the length-to-width ratio should be carefully considered when choosing this cut and should be between 1.33 and 1.66.
The marquise cut resembles the oval cut, but ends in two points. In addition, this cut makes the diamond appear much larger. A marquise-cut diamond looks particularly beautiful in a setting flanked by two round stones. Care must be taken in selecting the colour because of the points; a colour grade between D and Hshould be selected to avoid possible yellowish tints at the points. A good length-to-width ratio for a traditional marquise-cut diamond is between 1.75 and 2.25.
A pear-shaped or teardrop diamond has a single point and a rounded end. This cut is popular with fans of round diamonds seeking a more unusual shape. The elongated shape of the pear-cut diamond creates a subtle slimming effect of the fingers. Because of the point, care must be taken when choosing the colour grade. To avoid a slight yellowish tint at the point, a colour grade between D and H should be selected. A good length-to-width ratio for a traditional marquise-cut diamond is between 1.45 and 1.75.
The key features of the radiant cut are its trimmed corners, making it a popular and versatile choice. A radiant cut can be square or slightly rectangular in shape. As the rectangular proportions may vary, length-to-width ratios need to be taken into account. A radiant-cut diamond with a square shape should have a length-to-width ratio between 1 and 1.05, while a more rectangular shape will need a length-to-width ratio greater than 1.10.
The heart as the ultimate symbol of love is beautifully accentuated in the heart-cut diamond. The diamond's brilliance is similar to that of a round-cut diamond. Please note that a slight yellowish tint may be visible at the corners in colour grades of less than H. As the heart cut can be broad, balanced or elongated, the length-to-width ratio must be considered to ensure the heart cut has the expected shape when viewed it from above. A good length-to-width ratio is between 0.90 to 1.10.
The cushion shape has long been popular, with rounded corners and larger facets that increase the diamond's brilliance. Accordingly these larger facets also highlight the diamond's clarity, so that a high clarity grade of at least VSI (very small inclusions) should be selected. The length-to-width ratio is also critical; this should be between 1 and 1.05 for a square cushion-cut diamond and greater than 1.15 for a rectangular-shaped cushion cut.