What is a Good Diamond Cut?

Rough diamonds can be cut by experts to virtually any shape and size

Some of the most popular shapes are round, oval, princess, emerald, marquise, pear, heart, triangle and radiant. The cut of a polished diamond is the only human contribution to its beauty, fire and brilliance.

Because of its extraordinary ability to reflect light, the round brilliant diamond is the most popular shape today.

Cut determines amount of reflected light that exits through the top of a diamond. The better the cut, the more light exits through the top, the more brilliant and beautiful the diamond.

Is cut important? Many gemologists consider cut to be the most important diamond characteristic:

• A poorly cut diamond will appear relatively dull, even if clarity and color are perfect. When light is reflected through the sides and bottom of the diamond, not the top, brilliance and fire are dramatically reduced.
• The 'well-cut' diamond reflects almost all the light through the top; it will be the most beautiful, and the most valuable.

So, why don't we hear more about cut? Diamond sellers prefer to talk about carat weight, color and clarity. That's because those measures are relatively simple to explain:

• Carat weight is an exact measure
• Color is easy to determine by comparing the diamond to 'master stones'
• Clarity is a bit more difficult to judge, but there are well-established rules and standards that are accepted by all reputable diamond grading laboratories On the other hand, grading the cut of a diamond is complex. It is the analysis of all the diamond's proportions taken together that determines the cut grade.

Even the most reputable gemological laboratories try to avoid grading cut. In fact, only the AGS (American Gemological Society) has an established system for grading cut. Hopefully, the GIA, EGL, UGL will follow their lead.

How is cut graded? First, let's look at the parts of a diamond that are considered when evaluating cut:

Diameter
the width of the diamond as measured through the girdle
Table
the largest facet of a diamond
Crown
the top portion of the diamond; the crown extends from the girdle to the table
Girdle
the narrow band around the widest part of the diamond; the girdle separates the crown from the pavilion
Pavilion
the bottom portion of the diamond; the pavilion extends from the girdle to the culet
Culet
the facet at the tip of the diamond; diamonds of excellent cut have culets that are invisible to the naked eye
Depth
the height of the diamond; depth is measured from the table to the culet
To determine the diamond's cut grade:

• All the proportions of the diamond are considered
• All the angles between faces and facets are measured

The symmetry of the diamond is evaluated The final cut grade of the diamond is determined by its weakest component. For example, an 'extremely thin' girdle will result in a poor cut grade, even if every other measurement is ideal.

Remember: Only about 3% of polished diamonds are ideal cuts. They are exquisite and rare gems that reflect back 96% or more of the light that enters through the table.

No other diamond characteristic has so much impact on price!

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