What is the cut of a diamond

By 19.06 September 20th, 2018 No Comments

The rich and famous certainly have it good when it comes to designing and affording amazing engagement rings. They continue to blaze the trail in setting very inspiring trends. This is certainly where size does matter and it seems that there is a definite element of competition amongst celebrities as to who has the largest stones, most intense sparkle and most original designs.


What is the cut of a Diamond?

The use of diamonds in jewellery began in the mid-14th century and involved polishing the octahedral crystal faces into even facets called the Point Cut. In 1375 in Nürnberg a guild of diamond polishers was established. In the mid-15th century an improvement in cutting technique, involving the removal of part of the octahedron, resulted in the Table Cut, which appeared black to the eye, as seen in paintings from this era. The addition of four corner facets created the Old Single or Old Eight Cut. However, none of these early cuts revealed a stone’s dispersion. The more popular stones in these times were coloured gemstones such as rubies and sapphires, rather than diamonds.

In the late 1400s Lodewyk van Berquem, a Flemish polisher of Bruges, introduced the technique of absolute symmetry in the disposition of facets using a device of his own invention, the Scaif. He created pear-shaped stones known as pendeloque or briolette shapes. In the mid-16th century the rose or rosette was introduced in Antwerp. Then in the mid-17th century the first Brilliant Cut diamonds evolved known as Mazarins. In the early 18th century the general name of this cut was the Cushion Cut, known today as the Old Mine Cut. Later the Old European Cut was developed in the 19th century and this was the forerunner of today’s modern Brilliant Cut.

In the early 1900s Marcel Tolkowsky, with the advent of diamond saws and lathes, developed the Round Brilliant Cut. His development took both brilliance and fire into consideration and his calculations served the basis and general guidelines for future brilliant cutting techniques. In the 1970s Bruce Harding developed another mathematical design model and today laser cutting and computer-aided models are used to design diamond cuts.

Diagram of old diamond cuts showing their evolution from the most primitive (point cut) to the most advanced pre-Tolkowsky cut (old European). The rose cut is omitted, but it could be considered intermediate between the old single and Mazarin cuts.

The 4Cs to consider when purchasing a diamond are cut, colour, clarity and carat weight. The most critical aspect of a diamond is the way in which it is cut and polished as these directly affect the brilliance and sparkle of a stone. These attributes give diamonds their beauty, as well as their monetary value, when considered together with the other 4Cs of colour, clarity and carat weight of each stone. Cutting is the only aspect in which man has control and the ability to change as desired by the cutter. Patience and care are needed in order to acquire the best cut for each individual stone.

Rough diamonds generally have a dull, battered appearance and may be covered with a gummy, opaque skin. The cutting and polishing of these rough stones bring out each stone’s magnificence and beauty.

Cut refers to proportion, symmetry and polishing of rough stones, not to shape, the latter having many variables such as round, oval, square and marquise. A cut shows the style or design of each individual stone when shaping the stone for polishing. Cutting affects brilliance, sparkle and luminosity, all of which contribute to the overall finish of each cut stone.

Cutting constitutes a symmetrical arrangement of facets which shape the actual crystal. The type of cutting technique chosen for each rough stone depends on the shape and size of the rough stone. This affects the carat weight, while proportions affect the colour. Clarity is enhanced in the polishing, especially in the elimination of external blemishes, affecting sparkle, aesthetics and monetary value.

The factors to be considered before cutting and which ultimately will affect quality, GSI grading and pricing are:

  • proportions: affect light reflection and provide brilliance based on the table, width and depth measurements and ratios between size, angle and shape of each facet
  • symmetry: the precision of the facets, mirrors, windows and steps
  • brilliance: external brilliance or lustre is the light reflected from the stone’s surface and internal brilliance is the brightness of white light reflected from the rear facets
  • fire: dispersion of the spectrum of coloured rainbow colours determined by the crown’s height and angle, as well as the size of facets composing the crown
  • scintillation or sparkle: the arrangement and number of light reflections from the internal facets
  • finish: the glow and shine from the diamond’s surface.

Diamond Cut Proportions

The relationship between the size, shape and angle of each facet is of paramount importance in balancing the proportions for a stone’s ultimate brilliance and scintillation. About 20% of light reflects off or bounces back from the stone’s surface. About 80% refracts and bends on entering the stone while passing through the facets, but some will escape through the diamond’s base. Well-placed angled facets ensure that the maximum amount of light reflects back out of the top of the stone giving the diamond brilliance, scintillation and fire. The GSI grading is affected by how a stone interacts with light, determining its overall beauty and appeal.

shallow-diamond-reflection diamond shadows deep diamond reflection
Shallow Deep Ideal

If the cut is too shallow the light that enters the stone hits the pavilion (which acts as a mirror) at a low angle passing through the facets and leaving through the bottom of the stone.

If the diamond cut is too deep, light enters and strikes the first pavilion facet at an angle sharp enough to reflect to another pavilion: the light strikes the second pavilion at too low an angle, causing the light to pass through the facet and escape through the sides of the diamond.


It is important that the optimal cut must be balanced against maximum yield in order to maintain as much carat weight from the original rough stone. The cut grade allows a purchaser to identify Fair to Poor cut stones which are cut to gain carat weight, from Excellent, Very Good and Good stones where carat weight is not the priority.

The best cut for a diamond

The cut of the stone is directly connected to all the other quality characteristics.  How the diamond is cut influences the carat weight. The proportions affect the colour, and polishing reduces external blemishes, enhancing the diamond’s clarity. A well cut stone allows the maximum amount of light to strike each pavilion, with the light reflecting back through the table and the crown. Ideal cuts, termed excellent by the GIA, are proportioned perfectly with optimal facet angles and show good luminosity. These stones are valuable and command high prices.
If the buyer has a budget, then it would be wise to choose a smaller, well cut diamond rather than a larger, poorly cut stone, even if the stone has good colour and clarity. Rather forego a GIA grade in colour and clarity and spend more on a stone’s cut which will impact on the beauty of the diamond.

The most popular cuts and shapes are Most Brilliant: Round brilliant; Extremely Brilliant: Oval, Marquise and Pear; Very Brilliant: Heart and Princess; Brilliant: Cushion, Emerald, Asscher and Radiant and Less Brilliant: Baguette cut. A Heart shaped diamond may be cut shallow or deep, dull or brilliant, and while the heart shape remains, the cuts will be very different.

Brilliant Cuts, the considered standard for diamonds, such as round and marquise, hide inclusions better than step cuts found in emerald and asscher shapes. Fancy Cuts such as the Mixed Princess Cut and the Step Cut baguette are also popular and are used for various shapes. The cuts are evaluated by trained graders and the strictest standards are applied to the round brilliant. Step Cuts are used for rectangular or square stones and the Emerald Cut is specific for a cut with truncated corners. Other forms of the Step Cut include the Triangle or Trilliant Cut, the Trapeze or Trapezoid Cut, the Kite Cut, the Lozenge Cut and the Obus Cut. The Asscher Cut, a square modified Emerald Cut, is also popular.  There are also several other Mixed Cuts.


The Gemological Institute of America’s (GIA) grading table is shown below.


Maximum fire and brilliance. Reflects nearly all of the light that enters the diamond, creating exceptional sparkle and life.

Very Good

Properly reflects most of the light that enters the diamond, producing superior fire and brilliance. Under normal lighting conditions, appears very similar to Excellent Cut, but for a lower price.


Reflects a majority of the light that enters the diamond, for an above average appearance. An excellent value compared to higher cut grades.


Allows much of the light entering the diamond to escape from the sides or bottom, reducing perceived fire and brilliance. More acceptable in diamonds of less than .75 carats, where differences in sparkle are more difficult to perceive.


Allows most of the light entering the diamond to escape from the sides or bottom. The diamond may appear noticeably dull and lifeless, even to an untrained eye.


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