Diamond Education

The 4Cs

When you’re buying a diamond, there’s only one reputable standard for quality and that is the GIA. As one of Perth’s engagement ring jewellers, all of our diamonds are certified by GIA. See below for diamond ring quality factors.

Established in 1931, GIA is the world’s foremost authority on diamonds, coloured stones, and pearls. A public benefit, non-profit institute, GIA is the leading source of knowledge, standards, and education in gems and jewellery. In the 1940s, GIA established the “Four C’s” and the International Diamond Grading System™ – to this day, the worldwide standard for evaluating diamond quality

Therefore, for round brilliant cut diamonds, GIA considers how a diamond’s proportions relate to each other, rather than considering individual proportions in isolation.

Components of a Diamond

All diamonds are made up of certain structural features. A diamond’s anatomy, or its basic structure, determines its proportions, brilliance, dispersion and scintillation. In total a diamond has fifty-eight facets with five main components. They are Table, Crown, Girdle, Pavilion and Culet.

GIA researchers proved that while every individual facet matters, a diamond’s appearance arises from the combined contribution of all its proportions. Even though all of a diamond’s parameters might be within the limits for a particular grade, a diamond might actually receive a lower cut grade when the parameters interact in a negative way to lessen a diamond’s appearance.

Therefore, for round brilliant cut diamonds, GIA considers how a diamond’s proportions relate to each other, rather than considering individual proportions in isolation.


Table Size

The table is the top horizontal facet of the diamond. The average table size is expressed as a percentage of the diamond’s average girdle diameter. While an ‘Excellent’ grade diamond will have a table size between 52 and 62 percent, other proportions are important too. Remember that GIA doesn’t consider individual proportions in isolation.

Lower Girdle / Half Facet Length

This ratio is measured by calculating how long the lower girdle facets are relative to the length of the pavilion. This defines the contrast of a round brilliant cut diamond, which controls the brilliance of a diamond. The well-cut diamond will range between 65 to 90 percent. Diamonds with longer lower half facets will have a little more scintillation.

Crown Height

The crown is the upper portion of the diamond, from the top edge of the girdle to the table. The average crown height is expressed as a percentage of the average girdle diameter. It can affect both the dispersion and brightness of a diamond.

Total Depth

The diamond’s overall depth from the surface of the table to the culet, expressed as a percentage of the average girdle diameter.


The culet is the small facet at the bottom of a diamond intended to prevent chipping and abrasion to the point. The culet size can affect face-up appearance and it’s described as the average width of the facet. Size is expressed as none, very small, small, medium, slightly large, large, very large, and extremely large. When there is no culet, it is sometimes referred to as a pointed culet. Preferably the culet will not be visible with the unaided eye, and when described as none (no culet), very small or small on a GIA report, it falls in the excellent range.

Crown Angle

The crown angle is the angle that’s formed where the bezel facets meet the girdle plane. The crown angle in a well-cut diamond will be within 31.5 to 36.5 degrees. The crown angle has a large effect on the face-up appearance of a round brilliant cut diamond. The best range of crown angles provides a route for exiting light dispersion, as well as additional contrasting directions for entering light. Star Length: The horizontally projected distance from the point of the star facet to the edge of the table, relative to the distance between the table edge and the girdle edge. A well-cut diamond will range between 40 to 70 percent when other parameters are within the correct ranges

Griddle Thickness

The girdle is the middle portion of a diamond, a narrow section separating the crown from the pavilion, and functions as the diamond’s setting edge. The girdle thickness is described as a range from its thinnest to thickest areas. A thick girdle is less desirable because it unnecessarily adds weight to the stone where it matters the least (making the diamond appear smaller). An extremely thin girdle is sometimes referred to as a knife-edge, and results in a diamond that is more fragile and susceptible to chipping. Therefore, a girdle that is “medium to slightly thick” is preferred.

Pavilion Depth

The pavilion is the lower portion of a diamond from the bottom edge of the girdle to the culet. The pavilion depth is expressed as a percentage of the average girdle diameter. A pavilion depth that’s too shallow or too deep will allow light to escape from the side or bottom of the stone. A well-cut diamond will direct more light upward through the crown.

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