The diamonds available in the markets are derived from rough stones mined from beneath the earth. It is not difficult to visualize then why the cut of the stone has the deepest impact on its value.

Experts in cutting diamonds can give it any shape/size in the world. Some shapes or cuts have however gained more popularity than others over time such as the round, oval, princess, emerald, marquise, pear, heart, triangle and radiant. The touch of the diamond cutter is the only human contribution to the outstanding beauty, fire and brilliance of this product of nature.

Popular Diamond Cuts
Round	Oval	Pear	Princess	Radiant	Heart	Triangle	Emerald	Marquise

Among these, the round brilliant diamond is most coveted owing to its higher ability to reflect light. It is the cut that enables maximum light to emanate from the top of the diamond; and the more efficient the cut, the more light the diamond gives out and in turn makes it more beautiful and expensive.

Cut is considered to be the most important attribute of a diamond by most gemologists. As seen in the diagrammatic representation below:

The wrong cut reflects more light from the bottom or sides of the diamond than from the top and even if the color is right and clarity of the best grade, the stone will not shine to its full potential. Only the diamond that gives out light from the top looks the most beautiful and is consequently more expensive.

So, why don't we hear more about cut?

Most diamond sellers will talk about carat weight, color and clarity because those features are relatively easier to explain and the standard grades of GIA and AGS make life simple.

With regard to cut, only the AGS (American Gemological Society) has an established grading system because this is a complex task involving many aspects of the diamond's proportions.

How a cut is graded?

It is necessary to become familiar with the components of a diamond before evaluating cut:

Legend:
DIAMETER:	the width of the diamond as measured from the widest part of the diamond i.e. the girdle
DEPTH:	the total height of the diamond measured from the top of the table to the tip of the culet
TABLE:	the largest facet of a diamond which is on top of the diamond
GIRDLE:	the widest part of the diamond that divides the diamond into two parts
CROWN:	the top portion of the diamond extending from the girdle to the table
PAVILION:	the lower portion of the diamond that stretches from the girdle to the lowest point of the diamond
CULET:	the facet at the lowest tip of the diamond which in the best diamonds are invisible to the naked eye

The cut grade of a diamond will take into account:

All physical proportions of the diamond ~ All angles between faces and facets ~ The symmetry of the diamond

Only that diamond is considered Ideal Cut which fulfills all the above mentioned criteria in the right proportions. Any single weak component with bring down the cut grade of the diamond. A diamond with a very thin girdle for instance will take it to the poor cut grade, irrespective of the fact that all other measurements are ideal.

How cut affects price

A single carat, round brilliant diamond with superior clarity and F color will have different values depending on the type of cut, as you can see below:

Cut	Ideal	Very Good	Good	Fair	Poor
Value	$7,800	$7,000	$6,000	$4,000	$2,800

The fact is that less than 5% of polished diamonds are Ideal Cuts; and it is their exquisite ability to reflect back the maximum light that enters through the table that makes them rare gems.