Diamonds generally have very different characteristics. For example, if you look at two diamonds of the same size, you might assume that they are both worth the same. However, this is not entirely true, because even if there are only small differences, the effect of a diamond and its value are completely different.
The best-known criteria for classifying a diamond in terms of quality and value are the so-called Four Cs: Carat, Clarity, Color and Cut.
Carat (Carat)
Carat is the unit used to indicate the weight of a diamond. One carat weighs 0.2 grams and corresponds to 100 points - so a 0.5 carat diamond weighs 0.1 grams and corresponds to 50 points.
It is important to know that the carat only indicates the weight of the diamond, not its size. Therefore, a two-carat diamond is not twice as large as a one-carat diamond, even though it weighs twice as much.
Two other factors are important in determining the size of a diamond:
The dimensions of the diamond in millimeters
The quality of the cut, i.e. the cut execution and the proportion of the diamond
Interaction between diamond size and diamond weight
View size chart
When the diamond is worn in a piece of jewelry, an optimal cut of the upper half of the diamond is particularly important for its appearance of size, since the lower part of the stone is usually hidden in a setting . This is because an optimal cut increases the light reflection in the stone and thus makes the stone appear larger.
In addition, proportions should be taken into account when cutting a diamond; two different stones can appear different in size due to their proportions, even if they have the same carat number, if a large part of the weight is in the lower, invisible part of the gemstone.
On this list we have shown some diamond shapes in different carat numbers so that you can get an idea of the approximate size of the diamonds.
To view the diamond size and weight table you will need Adobe Acrobat Reader. Please ensure that the document is displayed in 100% view so that the proportions are displayed correctly.
Clarity
Diamonds and their purity – inclusions as a quality criterion of the 4 Cs
Clarity describes the purity of a diamond. It is rare to find diamonds that are "flawless", i.e. absolutely flawless , even under tenfold magnification.
Most diamonds contain foreign bodies or crystal defects, known as inclusions, which affect their clarity. Inclusions can be enclosed minerals (natural ones like a diamond in a diamond or foreign ones like zirconia in a sapphire), natural cracks or growth phenomena. These inclusions prevent light from penetrating the stone unhindered and reduce reflections and the coveted sparkle. The smaller and fewer inclusions a diamond has, the more valuable and purer it is.
The clarity grading of diamonds is based on a generally valid scheme – the clarity scale of diamonds ranges from the best level IF (flawless) to P3 (larger features):
Diamonds with clarity P1 to P3 have inclusions that are visible to the naked eye . They describe the stages from Clear Features (Piqué I) to Major Features (Piqué II) to Coarse Features (Piqué III).
In the four other clarity levels of diamonds, the inclusions in the stone can only be seen at tenfold magnification.
The highest and best clarity level is FL / IF – a diamond of this clarity is absolutely flawless or internally flawless and has no inclusions whatsoever.
The next best clarity grades are VVS (very very small inclusions) and VS (very small inclusions), which means that the diamond has very, very small to very small features.
The last level of diamond clarity under ten-fold magnification is SI (small inclusions). Diamonds with this clarity level have small features in the stone.
Colour classifies the colour of a diamond. Diamonds come in all colours, although yellowish tones are the most common - these are assessed together with colourless diamonds when grading, as their yellowish colour is not intense enough to be called absolutely yellow diamonds. The basic rule when assessing colour is: the more colourless the diamond, the more valuable it is! With an absolutely colourless diamond, white light penetrates the stone effortlessly and emerges again in rainbow colours.
Diamonds in full colors (green, red, blue, purple, brown, yellow and black) are called fancy diamonds. They are subject to their own grading standards and can therefore be even more valuable and expensive than pure white diamonds, depending on the color and intensity.
Fancy diamonds are caused either by impurities in the diamond or by uneven pressure during formation. Statistically speaking, there is on average only one fancy diamond in 100,000 diamonds.
Internationally valid terms for the color of diamonds
Cut refers to the cut of a diamond. Cut refers to the type and shape of diamonds created by grinding. The cut serves to enhance the diamond's shine and to emphasize the optical effects inherent in the stone.
A well-cut (or faceted) diamond, regardless of its shape, reflects the incoming light optimally, is more brilliant and the cut gives it the special fire that makes it so desirable.
If the diamond cut is too deep, light rays will escape through the bottom of the diamond; if the cut is too shallow, the light ray will be refracted back into the interior at the top and will also escape through the bottom.
Only with good cut proportions is the light reflected from one facet to the other and then shines back through the top of the diamond.
Anatomical conditions for optimal diamond cutting
Every diamond, regardless of its shape, has the typical octahedral crystal structure. Furthermore, the stone has only a few cutting planes and only a few cutting directions in each cutting plane:
Without exception, every rough diamond has four three-point grinding planes (4 x 3), six two-point grinding planes (6 x 2) and three four-point grinding planes (3 x 4) - so every diamond has a total of 36 soft grinding directions. All other approximately 100,000 (360 x 360) directions are hard. Deviations of just a few degrees from the actual grinding direction cause the diamond's hardness to increase to such an extent that it can hardly be cut any more.
These anatomies are important for a good cut:
- number of facets and their distribution
- Symmetrical and sized arrangement of the facets
- Angle of facets to girdle plane
- Proportions of the table and of the table to the top height
- size ratio of top to bottom
- Thickness of the girdle and culet
- Percentage of the total height of the diamond (total height divided by diameter)
The cut grading of diamonds
The brilliance of a diamond is determined by the so-called finish and evaluated by the following cut gradings:
- Excellent (≙ ideal): Very rare and exquisite. Exceptional brilliance, no features, best proportions and symmetry. The light entering the diamond is perfectly reflected.
- Very good: Very good brilliance with few or only minor external features. Very good proportions and symmetry.
- Good: Good brilliance with some external characteristics. Proportions with minor deviations, good symmetry of the facets.
- Fair: Slightly less brilliance with several major external features. Proportions and symmetry with larger deviations.
Round
The brilliant cut is the most popular and most researched diamond shape. Many theories of light behavior are aimed solely at optimizing the brilliance of the diamond.
The cut offers high flexibility in choosing the cut quality, color and clarity, as the brilliance and fire are always present.
Ideal/excellent cuts with excellent symmetry and luster bring out the highest brilliance in the diamond.
Princess
Princess is particularly popular for engagement rings due to its brilliance and cut. Originally, its shape was square, but today it is increasingly cut rectangularly.
Due to the four sharp and exposed corners, at least color H should be chosen to avoid slightly yellowish discoloration. In addition, the length-width ratio should be chosen optimally.
Emerald
Emerald looks similar to Princess at first glance, but is cut differently at the bottom.
The rectangular facets and its large, open table particularly emphasize the purity of the diamond.
Therefore, a clarity grade of at least VSI is best suited for the emerald cut. In addition, a length-width ratio of 1.30 to 1.40 should be chosen for a standard emerald shape.
Asscher
The Asscher shape is very similar to the emerald cut, but in contrast is cut exclusively square.
Here too, a clarity grade of at least VSI should be chosen due to the anatomy of the cut. It should also be noted that with color grade J and above, slightly yellowish spots can appear in the corners and edges of the diamond - a higher color grade is therefore more optimal.
Oval
Oval-cut diamonds have a similarly strong brilliance to round-cut diamonds. This shape particularly beautifully accentuates long and slender fingers.
As with the Princess and Emerald Cut, the length-to-width ratio of the oval cut should be checked – it should ideally be between 1.33 and 1.66.
Marquise/Navette
The marquise or navette cut is very similar to the oval cut, but has two points, which makes the diamond appear larger.
Because of the two points, a color between D and H should be chosen to avoid yellow spots. In addition, the traditional marquise shape requires a length-width ratio of 1.75 and 2.25.
Pear (drops)
The unusual pear cut is also called a drop cut because it has a round and a pointed end that closely resembles a teardrop or drop.
Due to the pointed inlet, a color between D and H should also be chosen here. The optimal length-width ratio for the teardrop cut is between 1.45 and 1.75.
Radiant
The key features of the radiant cut are its broken corners. This makes it universally applicable and therefore very popular.
The radian can be either square or slightly rectangular. The optimal length-to-width ratio for the square radian is 1 to 1.05, and for the rectangular radian 1.10 and larger.
Heart
With the heart cut, like the round cut, the brilliance is beautifully highlighted.
However, due to the special shape, a color level of at least H should be chosen here to avoid slightly yellowish spots in the tip and the upper notch.
A good length-width ratio for an optimal heart shape is between 0.90 and 1.10, but can vary depending on the diamond and preferences.
Cushion
The cushion cut was particularly popular in the past – its rounded corners and large facets make the diamond sparkle particularly beautifully.
As with the brilliant cut, a high clarity grade of at least VSI should be chosen because of the large facets.
For a square cushion, a length-width ratio of 1 to 1.05 is optimal, whereas for a rectangular shape, a ratio greater than 1.15 is recommended.
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