Anatomy of a Round Brilliant Cut Diamond

Anatomy of a Round Brilliant Cut Diamond

Round brilliant cut diamonds are famed as the King of the diamond world and are loved universally for their incredible sparkle and beauty. There is however a lot more than meets the eye when it comes to the round brilliant. By far, the most popular and most studied diamond shape, the round brilliant cut diamond has a complex anatomy that has been carefully devised to maximise sparkle. Here we outline each part of the round brilliant cut diamond and explain the contribution each part plays towards the sparkle of a diamond.

Facets:

Diamond facetsThe standard round brilliant cut diamond has 57 or 58 facets. Facets are the surfaces of a diamond that can be polished. These facets can then refract the light within the diamond and give off the spectrum of beautiful colours. The following facets comprise a round brilliant cut diamond:

1 Table Facet

8 Star Facets

8 Kite facets

16 Upper Girdle Facets

16 Lower Girdle Facets

8 Pavilion Mains Facets

1 Culet (optional)

The Crown of the Diamond

The crown of a diamond is the upper part of the diamond.  It consists of four types of diamond facets: the table, star facets, bezel/kite facets and the upper girdle facets.

The Table Facet

The size of the table facet is one of the most important factors in the appearance of any finished diamond. As the largest top facet, the table lets light into the diamond and refracts it towards the facets on the top and sides of a diamond. It is important that the table facet is balanced i.e. not too big and not too small in relation to all the other facets.

The table percentage of a round brilliant diamond is the average of four table measurements (from bezel point to bezel point) and is expressed as a percentage of the average girdle diameter. It is reported to the nearest whole percent (1%).

Top Tip:

For round brilliant cut diamonds, look for a table that takes up between 54 and 60 percent of the diamond’s overall width. These measurements are considered well balanced and should maximise light performance.

8 Star Facets:

The length of each star facet is very important and is expressed as the star length percentage.

Star facets that are very long or very short can have a negative impact on sparkle.

8 Bezel / Kite Facets & 16 Upper Girdle Facets

These facets if not properly lined up or if too deep or too shallow can negatively impact a diamond’s face up appearance. The crown angle is the measured angle between the bezel facet plane and the table plane. The average of eight crown angle measurements is reported to the nearest half of a degree (0.5°). This angle together with the crown depth percentage is extremely important as they determine the amount and the quality of the light that produces this brilliance.  Without a properly executed crown, a diamond would show little brilliance, if any.

The Girdle

The girdle is best described as the thin perimeter of a diamond that divides the crown above from the pavilion below. A diamond girdle can be finished in a number of ways however most round brilliant cut diamonds now have faceted girdles as per best practice principals. The girdle is graded by measuring it at various points along the girdle to determine its thickest and thinnest points. If the measurements are even and fall into the same category, then the girdle will be given a single rating stating simply Thin, Medium etc. Should there be variations in the measurements, the rating will depict the slimmest and widest grade of the girdle and terms like Very Thin to Medium can be noted. Extremely thin girdles are best avoided and girdles with large variations in measurement should be inspected carefully. A perfectly proportioned diamond would have a Medium girdle rating, though ratings close to Medium often also score excellent cut grades.

The Pavilion

The pavilion is the lower half of a diamond. The pavilion of a round brilliant cut diamond has two types of facets or 3 if a culet is present. Eight pavilion mains and 16 lower girdle facets and a culet form the “lower halves” of a diamond. Small deviations in pavilion angles can have a huge impact on the diamond’s face-up appearance. Steep pavilion angles can produce very dark areas under the diamond’s table. An ideal pavilion angle will bounce light from one side to another, and then send it back through the table facet again, thus creating the perfect return of light to the eye that we see as sparkle.

The Culet

It is most common nowadays for round brilliant cut diamonds to have no culet facet. Older diamonds often had large and visible culets and today the preference is for none. The culet size is expressed as the width of the culet facet relative to a round diamond’s average girdle diameter. When a culet is present, it is rated from None to Extremely Large. Unless you’re looking at an antique or vintage diamond, it is best practice to choose a stone with a small culet or none at all, as this will display the diamond’s fire and brilliance to the best effect.

As you can see there is a lot of thought that goes into fashioning the perfect round brilliant cut diamond. Cut quality is the least understood of the 4Cs however it is arguably the most important. High quality certified diamonds with excellent cut, polish and symmetry grades have been devised to optimise light performance and sparkle and are some of the most beautiful diamonds on the market. If you are looking for a high quality diamond with maximum sparkle, remember that cut is key to effecting a truly striking diamond.

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