The 4 C's

A Diamond's Cut

Cut is considered by many to be the most important "C." A poorly cut diamond, no matter how great its color and clarity is, will not compare in sparkle and flicker to a better cut diamond with comparatively lower color and clarity. There are several types of cuts such as asscher and cushion.

There will always be different opinions on the best diameter of the largest facet on the top of the stone and the best depth for a diamond, because these factors alone are not sufficient to accurately judge a diamond's cut. Other diamond factors such as crown angle, girdle thickness, pavilion depth-percentage, cutlet size, polish, and symmetry also play a role in judging a diamond's overall cut quality and should also be learned.

Diamond Cut Chart

Each lab uses its own terminology which can sometimes be confusing. For example, GIA calls its top grading "Excellent" followed by “Very Good”, while other labs use the terminology “Very Good” as their top grade. A diamond graded “Very Good” by GSL, for example, would therefore be the equivalent of a diamond graded “Excellent” by GIA.

GIA: Excellent - Very Good - Good - Fair - Poor

HDR: Very Good - Good - Medium - Fair - Poor

AGS: Ideal - Excellent - Very Good - Good - Fair - Poor

DCLA: Excellent - Very Good - Good - Medium - Poor

GSL: Very Good - Good - Medium - Poor

While grades are not the same, it is typically recommended to buy a diamond with a “Good” grade or better regardless of who has provided a certificate. It’s not recommended to buy diamonds with grades of “Medium”, “Fair” or “Poor”, as the alignment of their facets may misdirect light so severely that it affects the brilliance of the diamond.

color grades

Other Factors Affecting Cut

Proportions are not the only thing that affect cut. There are other factors that have to do with the type of geometry, and quality of the end result.

Girdle Thickness

In round diamonds, a thin to medium girdle is preferred (too thick will result in smaller diameter for the respective weight; too thin has durability issues). This can vary with fancy shapes. For example: shapes with sharp points are vulnerable to damage, so a thicker girdle ensures better durability. Side note: girdles can be faceted, polished, or bruted.

Presence of Cutlet

A culet is the pointed tip where the pavilion meets. It’s better to have no culet or a small one. Bigger culets can look like inclusions.


Refers to how consistent the diamond facets are. One misshapen facet can affect the facets surrounding it, setting off a chain reaction affecting angles, and reducing brilliance. Sometimes symmetry flaws are introduced on purpose in order to remove an inclusion and get a higher clarity grade. Poor symmetry affects the reflection of light so its better to stick with “very good or excellent” symmetry for round diamonds. Fancy shapes should be evaluated on a case-by-case basis, but the symmetry grade can be "very good" and "good must be evaluated".

Common symmetry flaws include:

  • Off center table or cutlet
  • Unequal facets
  • Misshapen facets
  • Wavy Girdle
  • Non-parallel table and girdle


When viewed from the top (crown), an ideally cut diamond should reveal eight symmetrical arrows. On the other hand, when the diamond was viewed from the bottom (pavilion), it should reveal eight symmetrical hearts.

Due to the extreme level of cutting precision required for symmetrical patterning, Hearts and Arrows diamonds are sometimes called “super ideals”. Fast forward to modern day, the term “super ideal” is used to define a diamond with superior light performance, material quality and precise optical symmetry.

So does an “Ideal” Cut Rating equate to Hearts And Arrows? The answer is NO. Not all diamonds with an ideal cut rating (AGS) or excellent cut rating (GIA) will automatically qualify it as a hearts and arrows diamond. Technically speaking, the formation of a precise H&A patterning is due to extreme care that is taken when polishing each facet to exact angles and proportions. This level of precision goes way beyond the criteria needed to achieve a “excellent” symmetry rating.

Also, taking a great picture or viewing the hearts and arrows patterning isn’t a straightforward process. It does require some practice especially if you had no prior experience. Any slight tilt of the diamond or your eye (even by a minute 0.5 degrees) would cause the patterning to be slightly skewed. Do bear this in mind when you are physically examining diamonds in stores.

Signs of a poorly cut stone

Aside from a lower level of brilliance and light return, there are several telltale signs of a poorly cut diamond. Keep these in mind when shopping for a stone.

Bow Tie

In longer fancy cut shapes like oval, marquie, or pear, there will often be black patches resembling a bowtie across the width of the diamond’s body. This occurs when the facets do not reflect light properly, and if it is present, you will see these black patches no matter which way you turn or tilt the diamond. Bowties occur due to light obstruction while viewing the stone, not light leakage. The actual process of “viewing” the diamond creates this effect—when an observer looks at a stone, the light rays travelling to the stone are literally blocked by the viewer’s head, which creates dark shadows that reflect within the stone. The cutter can possibly eliminate or lessen the intensity of bowties, but it may not actually be economically feasible to do so (loosing too much weight = less profit).

On the bright side, slight bowties can actually give fancy shaped diamonds an appealing look that defines its overall character. The bowties that you want to avoid are the ones that black out a large area. Bowties will almost always appear to some degree in fancy cuts like ovals, marquises, and pears, but the presence of a bowtie does not automatically render a stone worthless. If these stones were actually cut to completely eliminate any insidence of bow-ties, they’d generally be cut to dismal proportions and would have issues with brilliance. Just look for a stone where the bowtie blends in well.

Bowties are never mentioned in grading reports, and online diamond distributors can’t always provide you with visual assurance—so be careful during purchases!


When diamonds are cut too shallow, the internal reflections of the girdle can be seen in the table fact, creating an image of a gray ring that is visually distracting. These stones suffer from a lack of brilliance, and the ring can sometimes resemble an I3 type inclusion. The severity of the fish eye can depend on factors such as:

  • Shallow pavilion angles — shallow depth can cause light rays to be reflected from the girdle back through the table. The light reflects in a way that causes less brilliance and makes pronounces cut defects
  • Large table facet — Larger tables reduce refraction
  • Girdle thickness — girdles leak light

Fisheye can occur in fancy shape diamonds as well! Shapes like ovals, pears, and hearts can exhibit this effect if they are cut with a bad combination of angles. The fish eye phenomenon is an indication of a very poor cut, which makes any diamond dull and lifeless.

Evaluating Light Performance

If you have 3 GIA triple excellent diamonds, how can you tell which one has the best light performance? This is where tools like the ASET (Angular Spectrum Evaluation Tool) and IdealScope come in.

The ASET scope provides more information with regard to light performance. For fancy cut diamonds especially, the ASET is the preferred tool for evaluating light performance. However, it does take more knowledge to decypher what the colors mean and how the relate to the diamond's optics.

The simplicity of the IdealScope brings a certain degree of lucidity to the table. You do not really need any gemological qualification to figure out which aspects of an idealscope image to pay attention to. Red is desirable and indicates light return while diamonds with too much white areas indicates problems with light leakage.

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