Why a Diamond’s Cut is So Important

A diamond’s cut determines how much light the stone reflects. The diamond may have great colour, clarity and carat, but if it reflects only a little light it will be dull and lifeless, while a diamond with a great cut will emanate fire, sparkle and allurement.

diamond cut

As we talk about diamond cut, don’t confuse it with diamond shape. A diamond’s cut refers to the symmetry of its facets, the measurements of its angles and much more. A diamond’s shape refers to its external form, which can be round, oval, cushion or heart-shaped, among others.

Before we explain more about diamond cut, let’s briefly consider how diamond cutting has evolved since it first began in the Middle Ages.

The History of Diamond Cutting

Rough diamonds come in all shapes and sizes and in their natural state are far from spectacular. Diamonds must be cut to reveal their inner beauty.

Jewellers first began to realize this in the middle of the 1400s. They discovered that the crystals within rough diamonds were octahedrals and began polishing these 8 natural facets to  improve the stone’s usability and beauty. This form of polishing diamonds is now known as the point cut.

Rough diamond octahedronJewellers worked to improve the point cut over the next decades. They began to saw off a portion of the octahedron to form a flat table on the top of the gem, as well as added a culet to the bottom point of the gem to prevent it from cracking. During these years, a Flemish diamond polisher named Lodewyk van Bercken stressed the importance of each gemstone being absolutely symmetrical.

In the 16th and 17th centuries, jewellers experimented with adding additional facets to diamonds. Rosette-cut diamonds with triangular facets arranged in a radiating pattern were introduced to the diamond market in Antwerp, while Peruzzi-cut diamonds with 33 facets on their crown became popular in Italy.

Each of these early diamond cuts contributed to the development of the old European cut in the 1800s. The Old European cut gave diamonds 58 facets, as well as a smaller table, larger culet and more depth than their earlier counterparts. The old European cut set the stage for the round brilliant cut that we prize today.

As the 20th century dawned, jewellers began using more precise saws and state-of-the-art lathes as they shaped diamonds and a Polish engineer named Marcel Tolkowsky began to systematically study the old European cut. Tolkowsky carefully calculated how much white light old European cut diamonds reflected and evaluated the fire that appeared as the white light was dispersed in all the colours of the rainbow.

Marcel Tolkowsky then mathematically redesigned every aspect of the old European cut. His stunningly beautiful, new diamond cut became known as the round brilliant cut, because it maximized the brilliance, fire and sparkle of every diamond crystal.

European vs round cut diamond

Today approximately 75% of all the diamonds used in engagement and wedding rings, as well as other jewellery, are full of life and light thanks to the round brilliant cut.

Now let’s carefully consider the primary aspects of a diamond’s cut.

The Science Behind Diamond Cutting

The best gemologists take time to study the rough diamond, before they begin to cut it. As they study it, they consider its grain, any flaws that it has and its precise measurements. They then decide how to give it symmetry, proportion and polish to bring out the beauty in that particular stone.

Here is how gemologists explain symmetry, proportion and polish in relation to diamonds:

Diamond facet name

Symmetry – The best diamonds are perfectly symmetrical. This means that the facets on any of its sides are exactly similar to the facets facing them across the diamond’s axis.

Today’s round brilliant cut diamonds have 58 facets, if they have a culet, and 57 facets without a culet. Gemologists have named the facets so that they can be very specific in their work. On the crown of a diamond, the star, kite and upper girdle facets surround the diamond’s table, while lower girdle and pavilion facets stretch from the diamond’s girdle down to the culet.

 Proportions – A diamond’s proportions are almost always based on Tolkowsky’s ideal diamond design. Tolkowsky used the diamond’s diameter as the basis for his calculations and concluded that for optimal light reflection:



  • The total depth of the gem should be 59.3% of the diameter.
  • The diamond’s table should measure no more than 53% of the diameter.
  • The height of the diamond’s crown should be 16.2% of the diameter.
  • The depth of the diamond’s pavilion should be 43.1% of the diameter
  • The diamond should have a crown angle of 34.5 degrees.
  • Lastly, the diamond should have a pavilion depth of 40.75 degrees.
Tolkowsky Ideal Cut Proportions

As gemologists decide what proportions they are going to give a diamond, they pay special attention to the correlation between the diamond’s carat weight and its diameter. If they give a diamond with a small carat weight a large diameter, the resulting gem will be shallow and lose light through the sides. A heavy diamond with a diameter that is too small will also lose light through its pavilion because it is too deep.

To produce the ideal diamond, gemologists must find the perfect balance between a diamond’s carat weight and the measurement of its diameter, so that all the light that enters the stone will be reflected back out of the crown.

diamond cut light

Polish – One of the final steps in the diamond cutting process is polishing, because all diamonds pick up minor surface blemishes as they are cut and these flaws obstruct the reflection of light. Diamonds are polished with diamond dust and other abrasive agents to smooth the surface of the diamond, so that light can enter and exit the gem without interference.

Skilled gemologists pay attention to the symmetry, proportions and polish of any well-cut diamond, but on approximately 1% of diamonds they double their efforts in order to make hearts and arrow diamonds.

Hearts and Arrow Diamonds – The Japanese are credited with creating the first heart and arrow diamonds in the 1980s. Japanese jewellers optimized the diamonds’ symmetry, modified the faceting pattern and spent extra time polishing the stones. The result was exceptional diamonds that have eight internal, symmetrical arrows when they are viewed from the top and eight internal, symmetrical hearts when viewed from the bottom.

Hearts and arrows diamond

Today hearts and arrow diamonds are made by jewellers all around the world. Although they cost a little more than round brilliant diamonds, heart and arrow diamonds are worth the investment because they are exceptionally brilliant and have the special touch of having hearts hidden in them.

Understanding Brilliance, Dispersion and Scintillation

Throughout this article, we have mentioned again and again the importance of diamond’s reflecting light. When a diamond is cut correctly, light enters the top of the diamond, reflects from one facet to another, and then exits the diamond through the crown. This reflection of light creates brilliance, dispersion and scintillation and here is what we mean by these terms:

  • Brilliance – Brilliance refers to the intensity of the white light that reflects back through the diamond’s crown. Brilliance is the foundation for the diamond’s overall beauty.
  • Dispersion – Dispersion is sometimes also called fire. It refers to white light that has been refracted inside the diamond and then reflects out of the stone in the colours of the visible spectrum.
  • Scintillation – Scintillation refers to a diamond’s sparkle. A diamond with well-cut facets reflects small bursts of light at it moves or as the light around it moves and this causes the stone to sparkle.

The quality of a diamond’s cut decides how much light the gem reflects and this reflected light determines the stone’s brilliance, fire and scintillation. This is why diamond cut is so important and why you should purchase a diamond with a well-graded cut.

How a Diamond’s Cut is Graded

We have mentioned before how the best diamonds come with a diamond certificate from a reputable gem lab. A diamond certificate guarantees the stone’s value, as well as lists the gem’s primary characteristics including the grade of its cut.

As gem labs, for instance the Gemological Institute of America (GIA) or the Hoge Raad voor Diamant (HRD), grade a diamond’s cut, they calculate the proportions of the diamonds facets and then evaluate how successfully the diamond interacts with light to create brilliance, fire and scintillation.

The gemologists at the gem lab also asses the diamond’s design and craftsmanship, the correlation between its weight and diameter, the symmetry of its facets and the quality of its polish before they give it a grade which can be: Excellent (EX), Very Good (VG), Good (G), or Fair (F).

Diamond cut grade

At Beldiamond we advise our clients to purchase diamonds with either an Excellent or Very Good grade, so that it will have an even pattern of light and darkness across its surface, as well as be beautiful as it interacts with light. 

The Da Vinci Diamond Cut

This article would be incomplete if we didn’t mention the Da Vinci diamond cut. Leonardo Da Vinci believed that anything designed with the Golden Ratio (AC/CB = 1.618) would be outstandingly attractive. Da Vinci incorporated this ratio into innumerable sketches, paintings and articles. Just recently jewellers have begun using diamonds based on Da Vinci’s polygons and the Golden Ratio. The resulting gems are truly outstanding.

The Da Vinci Diamond Cut

Whether you are looking for a round brilliant, a hearts and arrows or a Da Vinci diamond, contact us and we will be happy to help you in any way that we can.