What makes a diamond so attractive? It’s probably the sparkle and the spectrum of light rays spilling out from the facets of the diamonds. This means that the cut is the most important factor when choosing a diamond. The basics are covered in our previous posts so we’ll go in depth to discuss the diamond anatomy here.
Read more: What does Diamond Cut really means?
Multi-faceted Diamond Anatomy
A modern round brilliant cut diamond has 57 facets plus 1 culet facet (if any). The cut grade takes into consideration the proportions and the angles of the facets in totality. Despite being small, the diamond can be divided into a few sections. Let us explore the diamond anatomy.
The table refers to the horizontal facet at the highest point of the diamond. It is measured in proportion with the diameter of the girdle. Here’s the confusing part, an excellent cut grade by GIA will have a table size between 52 – 62 percent. However, a diamond with a table size between 52 – 62 percent might not have an excellent cut grade.
Again expressed in proportion with the diameter of the girdle, the total depth is measured from the top to bottom of the diamond. In the same carat weight, a diamond with a lower depth percentage will appear larger than one with a higher depth percentage.
The crown starts from the upper girdle to the table of the diamond. It refers to the upper section of the diamond and is responsible for the diamond’s face-up appearance. It consists of a total of 32 facets: 8 stars, 8 bezels, and 16 upper halves.
The facets interact with the facets from the pavilion to disperse light to create the brightness, fire, and scintillation. Stripped away the industry jargons, they mean the colourless light (brightness), coloured light (fire), and the sparkle you see when you hold the diamond and move it (scintillation).
There are 3 proportions that are important in the crown section:
The height of the crown affects the light dispersion and brightness of the diamond. It is expressed as a percentage of the girdle diameter.
The crown angle is the average of all the angles between the bezel facets and the girdle plane. The crown angle of an excellent cut diamond is between 31.5 – 36.5 degrees.
The horizontal length of the star facet expressed as a percentage of the distance from the table edge to girdle edge. The star length of an excellent cut diamond falls between 40 – 70 percent.
Moving down from the crown, the pavilion refers to the lower section of the diamond. It starts from the lower girdle to the bottom point of the diamond and consist of 24 facets: 8 mains and 16 lower halves. Where needed, the diamond cutter will also cut an additional facet known as the culet.
The facets in the pavilion are responsible for reflecting the light back through the crown, where the light disperses. There are 2 important proportions in the pavilion.
The pavilion depth measurement starts from the bottom of the girdle down to the culet. It affects how much light will escape through the sides of the bottom of the diamond.
Similar to the crown angle, the pavilion angle is the average of all the angles between the main facets and the girdle plane. It is one of the important sections that affect the brightness of the diamond. A steep pavilion angle may create dark areas under the diamond’s table.
An excellent cut diamond by GIA will have a pavilion angle between 40.6 – 41.8 percent.
Lower Half Length
The lower half length is expressed as a percentage of the length of a lower half facet against the girdle to culet length. An excellent cut diamond by GIA will have a lower half length of 65 – 90 percent.
The girdle is the middle section of the diamond which separates the crown from the pavilion. It is also the used as the setting edge. The finish of the girdle (polished, faceted, or bruted) will also be stated on the GIA grading report. We recommend to avoid the bruted finish altogether and go for polished or faceted finishing.
The girdle thickness is graded using descriptions such as Extremely Thin, Very Thin, Thin, Medium, Slightly Thick, Very Thick, and Extremely Thick. On the grading report, it states the thinnest and thickest parts of the girdle in a range format, for example, Medium to slightly thick.
Avoid both extreme thicknesses; a knife edge is formed if the girdle is too thin and this makes the diamond fragile and more prone to chipping. An extremely thick girdle will result in ‘wastage’ as it adds unnecessary weight to the diamond. This makes the diamond looks smaller when compared to another diamond with the same carat weight.
Another thing to avoid is great variations between the thinnest and thickest points of the girdle, for example, “Very Thin to Extremely Thick” This is one of the signs of a poorly cut diamond. The recommended girdle thickness is medium to slightly thick.
A culet is a small facet found at the bottom end of the diamond. The main purpose of the culet is to prevent chipping at the bottom of the diamond. However, it will affect the face-up appearance of the diamond. In the GIA certificate, the culet is described as “none, very small, small, medium, slightly large, large, very large, and extremely large.”
An excellent cut diamond will have none (no culet), very small or small culet.
What Proportions Should We Go For?
As these proportions within the diamond anatomy affect the brilliance of the diamond, having an excellent grade should be the first priority. The minimum to go for is what we call a triple excellent diamond. It means that the cut/polish/symmetry grades on the GIA certificate are graded excellent. Here at Draco, we can explore with you to find the diamond that is the most suitable. Call us or book an appointment with us!