The cutting of a diamond is a highly skilled craft, and to become expert craftsman bench jeweler takes years of training. Diamond cut is not a simple matter of what shape the diamond appears to be. There are, in fact, a number of key elements that relate to diamond cutting that need to be considered when valuing a gem. The way a diamond is cut is the key to how it reflects light, and therefore the secret of its 'sparkle' - or 'brilliance'.

Proportions of a Diamond

A diamonds proportions are a key feature of the 'make' when a diamond is cut. The body of the diamond can be divided into two key parts. The upper face, visible to the world in any setting is called the 'Crown'.

The lower part of the body, usually more than half the depth of the gem, is called the 'Pavilion'. Whilst the pavilion may often hardly be visible, it is the internal facets of the Pavilion that create the important reflective surfaces that scatter light in the diamonds characteristically brilliant way back through the cut pattern of the Crown, and the flat table. The 'point' of the Pavilion is called the 'Culet' (pronounced rather like the word 'clay' but with an extra emphasis on the hard 'c' at the beginning - 'C'-lay).

Traditionally the Culet was actually formed as a final small flat facet. In older cut diamonds this is visible through the Table of the diamond as a small 'window'. It is a sensible way to finish the 'point' of the pavilion as it protects this otherwise vulnerable point from damage during handling, this is described as leaving the Culet 'open'. However modern demand now means that you often find a diamond Pavilion is brought to a fine point which is referred to as a 'closed' Culet.

The breadth of the Crown is called the Girdle, and the Table size refers to the width of the flat top surface of the gem. The depth of the gem from its Table to where the Pavilion begins is called the Crown height.

The combination of angles of the Pavilion, the Crown and the Table size create the overall appearance of the gem, and even slight differences can lead the diamond to look incredibly different. A skilled diamond-cutting expert will endeavour to create the best looking most attractive, most brilliant gem by exercising his experience in determining the optimum proportions of the gem he is creating.

In Perfect Symmetry...Or Not?

A diamond's symmetry is evaluated by how well the different aspects of its 'make' work individually, and in interaction. Therefore, a poorly 'made' diamond may suffer from such quality defects as: an off-center table, misshapen facets, or an out-of- round girdle.

Other indications of asymmetrical diamond cutting would be when a gem is judged to have a misaligned Crown and Pavilion, which occurs when the facets fail to meet perfectly. Indeed where the diamond cutting results in facets being precisely out of 'sync' the diamond is said to have a 'wavy girdle'.

It could well require the trained eye of a Gemologist, with the help of a loupe (10x magnifier), to recognize some of these deficiencies in make. Once again the inexperienced diamond purchaser needs to be careful that they are not purchasing a diamond that has a lower value than expected due to imperfect diamond cutting.

Diamond Cutting - The Art of Reflecting Light!

The true aim of excellent diamond cutting is to draw out of the diamond its extraordinary power to reflect light. A well cut diamond has three key effects on light that are the major attributes of its optical properties:

Sheer Brilliance

A 'brilliant' gem seems almost to glow with light. This very lightness can make even a less well-colored gem more full of light, or lighter in color than it may be truly graded. This factor, caused by white light reflecting from the diamonds inner facets, is enhanced by the perfection of the angular creation of the Pavilion, and the amount of light these inner angles reflect back through the crown of the gem.

On Fire

A diamond is often said to have 'fire' when it cause spectral dividing of white light into its colored components (like a prism). The technical term for this important factor that so impresses the eye, is 'Dispersion'.

A Wicked Sparkle

Perhaps the key, hard to emulate, characteristic of a fine diamond is its sparkle. The ability to seemingly throw-off 'sparks' as a gem is gently moved in the light is more accurately termed 'Scintillation'. More sparkle is generated by a larger number of facets and the perfection with which the cut diamond is 'polished'.

Documentating the Cut of a Diamond

Whilst the Gemological Institute of America (GIA), for example, does not have a formal grading system for cut, the GIA's Diamond Dossier - the document supplied with a diamond that has been officially assessed by a GIA qualified Gemologist - does list a stone's notable details.

For consistency, and accurate understanding, the grader always describes the shape of the stone using no special terminology or trade names. In the "Proportions" section of the Dossier the total depth of the stone and the percentage of the face of the stone taken up by the table are quoted. This section also lists the size and condition of the Girdle and the size of the Culet, too.

Under "Finish," polish and symmetry are rated as "excellent," "very good," "good," "fair," or "poor" - according to the assessment of the trained expert.

Be sure to see our related articles about factors affecting Diamond valuation: - Color; Clarity; Carats.