The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect colour and clarity, a diamond with a poor cut will have dulled brilliance.

The width and depth can have an effect on how light travels within the diamond, and how it exits in the form of brilliance.

Too Shallow: Light is lost out the bottom causing the diamond to lose brilliance.

Too Deep: Light escapes out the sides causing the diamond to appear dark and dull.

The actual measure of diamonds goes far beyond just the depth and width of the diamond.  Gemologist will look at each aspect of the diamonds anatomy, as illustrated below, to get a full picture of the diamond’s overall cut.  With today’s technology they can measure and determine the inter-relationships of each measurement with each other.  For example, the ratio of crown height to depth  or table diameter to overall diameter.  All of this can be modeled and determined with a computer. 

Diamond Anatomy

                                                

Polish and symmetry are two important aspects of the cutting process. The polish grade describes the smoothness of the diamond's facets, and the symmetry grade refers to alignment of the facets. With poor polish, the surface of a facet can be dulled, and may create blurred or dulled sparkle. With poor symmetry, light can be misdirected as it enters and exits the diamond.

One last detail that sometimes gets overlooked is the wether the girdle is polished.  In some cases the girdle of the diamond is not polished and results in a very dull white girdle that is not very pleasing once noticed.  Mostly you’ll find that the girdle has been polished and faceted.  Although its a small detail, it can sometime make a big difference in the overall look of the diamond.

Once all of the factors are taken into consideration by the gemologist they will then apply a grade to diamond with the following grades:

1. •Ideal:  Top grading for a diamond.  Virtually all of the light entering the diamond gets reflected back to the eye.
   

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3. •Very Good/Excellent:  Represents roughly the top 15% of diamond quality based on cut.  Reflects almost the same amount of light as the Ideal cut but for a better value.
   

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5. •Good:  Represents about 25% of the top quality diamonds based on cut.  Very nice looking diamond for the money.  Reflects most of the light back to the eye.  
   

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7. •Medium:  Reflects less light than a good cut.  Still a good looking diamonds and for a much less price. 
   

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9. •Poor:  Most diamonds in this range are either too deep or shallow.  Not a good choice as an engagement ring.  We do not carry or would sell diamonds in this cut category. 
   

After all of that you are probably wondering what is the best cut to buy.  Well the answer to that all depends on the other factors of the diamond as well as budget.  It would be safe to say that the Ideal cut grade is the obvious choice if money wasn’t an issue.  However, if it is, I would say a similar diamond (in clarity, colour and size) would also look stunning with a Very Good and Good cut grades.  Its comes down to personal preference and price.  Definitely stay away from diamonds in the medium to poor cut grades.

Cut

Clarity

Colour

Carat