There are essentially two types of diamond cuts: brilliant and step.
Brilliant cut diamonds are rough diamonds that were cut and polished in a form that gives them exceptional brilliance; they have mostly triangular or kite-shaped facets that radiate from their center whereas step-cut diamonds have square or rectangular shaped facets which are long, narrow, and parallel. When cut well, a diamond will be luminous; cut poorly, it will be dull.
Brilliant Cut Diamond
Step Cut Diamond
A crash course on the modern manufactured diamond cut
Today, the preferred diamond cut is set by the proportions and standards of the Gemological Institute of America. But the GIA didn’t pave the way. A Belgian-born gentleman named Marcel Tolkowsky, who was just 21 years old and boasted of being a mathematician, physicist and an engineer, set out to tell the world how to cut a diamond. He did all that in a 1919 paper called Diamond Design – A Study of the Reflection and Refraction of Light in a Diamond. (For the real rabbit hole enthusiast, you can view the published paper here: https://tinyurl.com/3r8t26s4 ) He effectively created the theory behind the round brilliant diamond, with the aim of being the most beautiful in terms of brilliance, fire and dispersion. He ultimately suggested a set of proportions which should be followed when cutting a diamond to make it the most beautiful. His suggested proportions would be further improved on by the GIA, resulting in the round brilliant cut diamond, considered the highest standard in terms of brilliance, fire and dispersion.
When we refer to the way the diamond is cut and polished to the form we see when we visit a jeweler, we are talking about diamond anatomy. Specifically, diamond anatomy refers to the elements of Proportion, Symmetry, Polish, Fluorescence and Facets.
Today’s diamond manufacturers follow proportions set by the Gemological Institute of America to cut and grade their diamonds. The GIA does not classify any diamond as ‘Ideal Cut’, rather, the highest cut grade is ‘Excellent’ as far as they are concerned.
Proportions in a diamond basically refer to the relationship between the measurements, percentage and angles of the facets. All of these different measurements contribute to a diamond’s display of brilliance and light dispersion and impact the final beauty and value of your diamond. Any deviation from these proportions will lead to light leakage from your diamond and affect the cut grade.
Proportions of a Diamond
The following gives an idea of the relative proportion that is recommended by GIA.
Table % – 52% to 62%
Crown Angle – 31.5° to 36.5°
Total Depth % – 57.5% to 63%
Crown Height % – 12.5% to 17%
Pavilion Angle – 40.4° to 41.8°
Pavilion Depth % – This (Pavilion Depth %) and pavilion angle are directly related to each other. If you increase the pavilion angle, the pavilion depth increases and if you decrease the pavilion angle, the pavilion depth decreases. This has a direct impact on the light return as it is responsible for total internal reflection.
Girdle Thickness% – Thin to slightly thick
Culet Size – None to small
What do these numbers tell me?
Because proportions impact the light return of your diamond, they will have a direct and noticeable impact on the overall beauty of your diamond. So, when choosing your diamond, go for the highest grade as far as proportion is concerned.
How do proportions affect price?
As with other parameters in your diamond, if your diamond has a proportion grade of ‘EX’ or ‘Excellent’, your diamond is more beautiful and consequently, more expensive. GIA does not give a proportion grade above ‘Excellent’.
The symmetry of a diamond has a direct impact on the pattern of reflection and this pattern of reflection affects the scintillation (how light is reflected off a facet) of a diamond. In fact, there is a romantic-sounding but actually quite practical term for diamonds showing a perfect pattern; these diamonds are known in the trade as ‘hearts and arrow’ diamonds. They are called this way because of the appearance of 8 hearts when looking down on the pavilion, and a set of arrows when looking at it from under the table. If your diamond is called ‘H&A’, it means your diamond has excellent optical symmetry.
Arrows are seen when a symmetrical diamond is viewed from the top
The modern round brilliant cut is a very symmetrical cut, which means that no matter how you divide the diamond, the arrangement of facets will follow a symmetry, or in other words, both halves will resemble each other when the diamond is visually divided. If the diamond has any feature that affects this symmetry, the symmetry grade is also affected. The common features that might affect the symmetry of a diamond are listed here: Table Off-center, Culet Off-center, Table/Culet Alignment, Irregular Girdle, Out of Round, Extra Facet, Irregular Facet, Open Facet, and Misalignment.
Out of all of these features, misalignment between the crown and pavilion and open facets are the most common symmetry variations found in a diamond. If your diamond has a ‘no or difficult to see’ misalignment or open facet, your diamond has an excellent symmetry rating.
What can a rating of ‘excellent’ symmetry mean?
As with other attributes, an excellent symmetry rating indicates the dedication and care put into planning your diamond for the cut, and ensures the best possible pattern of reflection in your diamond to make it the most beautiful.
How does symmetry affect the price of a diamond?
Like all other attributes of your diamond, a diamond with an excellent symmetry rating gives you the assurance of a beautifully cut diamond, though a little more expensive than those with a lower symmetry rating.
As you know, a rough diamond crystal is cut and polished on a wheel (known as a ‘scaife’) to make facets. These facets in turn act as windows and allow light to enter the diamond and bring out the coveted brilliance, dispersion and scintillation that diamond-lovers look for. (Confused by these terms? Check out our Glossary to clear things up.)
Facets allow the light to enter the diamond, but also allow the light to reflect back from inside the gem. The polishing process can even further enhance the combined external and internal reflection.
Diamond Rough
Polishing a Diamond
When evaluating the polish of a diamond for grading, many characteristics are taken into account, including features such as: Abrasion, Lizard Skin, Nick, Pit, Scratch, Burn Marks and Naturals. But mainly, the polish of a diamond is based on the presence of ‘Polish Lines’. Polish lines are the most common polishing variation found, and appear as transparent bumps present on the surface of a facet as a result of improper polishing. Presence of polish lines and other polishing variations have a direct effect on the scintillation of the diamond. According to the GIA, the highest cut grade of Excellent is possible in a diamond only when the polish grade of a diamond is either ‘excellent’ or ‘very good’.
What does an ‘excellent’ polish grade mean?
An excellent polish rating indicates that utmost care has gone into manufacturing the diamond to increase the scintillation, or reflectivity of its facets. Given a choice, you should go for excellent polish in your diamond.
How does polish affect diamond price?
As is true with other parameters, an excellent polish grade is what you should aim at. Although this will be more expensive, it ensures that you are getting the biggest, visually noticeable advantage in your diamond.
Perhaps you have noticed, let’s say, when out in a dance club or in a room lit with a UV light (because don’t we all hang out in one of these?), that your diamond ring or pendant is glowing? A cool and lesser-known fact about diamonds, both natural and lab-grown, is that about 25% of them visibly glow when exposed to ultraviolet light. When the light is removed, the glow stops. It’s called fluorescence, and it’s caused by the presence of defects in the diamond. A diamond can fluoresce weakly or strongly in any color, but blue is the most common color of fluorescence. Natural diamonds fluoresce differently from lab-grown diamonds, and knowing how to identify them can be an interesting way to impress your friends when you bring out your groovy black light at a party.
We should concern ourselves with fluorescence because fluorescence is graded by the GIA. It is believed that the more strongly the diamond glows, the higher the percentage of defects in the lattice and other elements, and the lesser the quality, and therefore cheaper, the diamond. Fluorescence grades mentioned in diamond certificates refers to the intensity or strength of this glow in response to UV light, more specifically under long wave UV light ( LWUV) . The GIA grades your diamond into one of the following grades, depending on the strength of fluorescence: None, Faint, Medium, Strong and Very Strong. Higher strength of fluorescence may affect the visual appearance of diamond, and consequently their market price. We want to put this phenomenon in perspective, however. Don’t let this feature worry you in your search for a great diamond. Only about 10% of diamonds exhibit fluorescence of such strength that their price is affected.
Diamond Rough Shines Blue if Florecence is Present
And what about phosphorescence? While fluorescence stops when the UV light source is removed, phosphorescence is the visible emission of light that remains afterwards. Phosphorescence does not affect the price of a diamond and hence it is not even graded or mentioned on the certificate. Phosphorescence in a diamond is extremely rare and occurs in .01% of stones. A stunning example of phosphorescence is the famous Hope Diamond, a 45ct blue diamond on display in the Smithsonian Institute, which glows an intense red long after exposure to a UV light source.
Should I worry about fluorescence in my diamond?
The presence or lack thereof when it comes to fluorescence is a debated topic. Do not choose a diamond where the fluorescence is so strong that it affects the color and transparency of your diamond. However, a slight amount of blue fluorescence can make your diamond look whiter and better. Anything is okay, as long as you like it in your diamond.
How does fluorescence affect price?
The most expensive diamonds are those with a ‘none’ fluorescence rating. Your final decision should be based on your judgment, based on naked eye evaluation. Unlike other parameters, where what is the best is well defined, fluorescence is an individual choice.
In jewelry, facets are the geometrically cut, flat surfaces that cover a gemstone. They act as windows through which light passes and is then reflected outward to produce a diamond’s sparkle. They can be produced in a variety of shapes and sizes, but whatever the shape or size, their purpose is to optimize the gem’s appearance. Generally, the more facets a gemstone has, the more sparkle it has, although the proportion and symmetry of the facets are equally important to the stone’s brilliance and fire.
Light enters and leaves the diamond through facets, so it stands to reason that the more facets a diamond has, the better. These facets, because of their placement and angle, lead to the reflection of light inside a diamond as well. You may be interested to know that a light beam is supposed to reflect about seven times inside a diamond before it exits and hits the eye. This amazing attribute contributes to a diamond’s brilliance and dispersion.
A round brilliant cut diamond has 57 to 58 facets. If the culet is faceted the facet count is 58 and if the culet is pointed, the facet count is 57. All the facets in a diamond have names assigned to them based on where they are located.
Close Up on Diamond Facets
Facets and Angles Allow Reflections of Light From Inside the Diamond
On the crown side there are a total of 25 facets:
Table facet – 1
Star facets – 8
Upper girdle facets – 16, placed as pairs
Below the girdle, which may be rough, polished, faceted, partially polished or partially faceted, there are either 24 or 25 facets:
Lower girdle facets – 16, placed as pairs
Pavilion main facets – 8
Culet – pointed or faceted
When it comes to the number of facets, the facet count is very important in a round brilliant cut. The facet count has to be either 57 or 58.
