Diamond Cut

Understanding Diamond Cut

Cut does not refer to a diamonds shape (e.g. round, oval, princess etc), it refers to a diamonds proportions, symmetry and polish. Many experts believe cut is a diamond’s most important characteristic and of the four C’s it has the greatest influence on the diamonds beauty. In simple terms it determines what we generally think of as sparkle.

Though it is extremely difficult to analyse and quantify, diamond cut has three primary effects on the appearance of the diamond: brilliance (the brightness created by the combination of white light reflections from the surface and inside the diamond), Fire (the dispersion of light into the colours of the visible spectrum, seen as flashes of colour) and scintillation (the flashes of light and dark or sparkle, when the diamond is moved)

Diamond proportions refer to the relationship between the size, shape and angle of each of the facets of a diamond. A wide range of combinations are possible and these ultimately determine the diamond’s interaction with light. When light strikes a diamond, approximately 20% immediately reflects off the surface (glare). Of the 80% that enters, a portion will escape through the bottom. A well proportioned diamond will have each facet placed and angled to maximise the amount of light that reflects back out of the crown (top) of the diamond to the eye of the observer. The reflected light is perceived as Brilliance, Fire and Scintillation.

Light Patterns

Diamond Cut

In the diagram above, three common light patterns are shown, when light meets any facet of a diamond it will either reflect (bounce back) or refract (bend while passing through the facet). The angle at which the light hits the facets determines whether the majority of it reflects or refracts, this is why cut is so important.

Evaluating the effect of facet shapes and angles, girdle width, culet size, polish and symmetry on the appearance of a diamond is challenging, even for professional gemologists. Fortunately, all of these factors have already been taken into account when calculating a diamond’s cut grade. Cut grade gives a single rating which weighs the combined impact of all the factors listed above on a diamond’s visual appearance. It is a simple yet vital tool in evaluating a diamond.

Understanding Cut Grade

Cut grade is assigned using the following scale:

Diamond Cut


Creates maximum fire and brilliance. Reflects nearly all of the light that enters the diamond creating exceptional sparkle and life.

Very Good

Reflects most of the light that enters the diamond producing superior fire and brilliance. Under normal lighting conditions, it appears very similar to the excellent grade.


Reflects the majority of the light that enters the diamond for an above average experience.


Allows much of the light entering the diamond to escape through the sides and bottom, reducing perceived fire and brilliance. More acceptable in diamonds of less than 0.75 carats,where differences in sparkle are more difficult to observe.


Allows the majority of the light entering the diamond to escape from the sides or bottom. The diamond may appear noticeably dull and lifeless, even to an untrained eye.

More About Diamond Cut

When a diamond is cut and polished from a rough stone, the cutter must balance the cut and therefore appearance against yield (cutting the diamond to maintain as much carat weight from the rough stone). Many customers are willing to pay more for a larger fair-cut diamond than for a slightly smaller well cut diamond. There is always pressure on the cutter to sacrifice appearance for weight.

Diamonds with an Excellent, Very Good or Good cut grade all show beauty however Very Good cut grades are most popular and give the best combination of value and beauty.