Cut is the only diamond value factor that is the result of human input. This important factor may be the most difficult to understand because it is the most technical, but gaining a basic understanding does not have to be daunting. Cut refers to the proportioning, alignment and finish of a diamond's polished faces or facets. Proper cutting enables a diamond to perform at its best and release its full potential for fire and brilliance. A well cut diamond will be more beautiful and more valuable than a poorly cut stone.

In addition, a cutter will usually have to sacrifice more of the rough stone to produce a well cut finished stone, thereby ending up with a smaller diamond than had he taken liberties with the cut. Well cut stones therefore yield less weight from the rough and are therefore more expensive to produce.

Fire, Brilliance, and Scintillation

These are the three aspects of diamond performance and they are distinct elements.

Fire refers to a diamond's ability to act as a prism and to break white light into its spectral colors. Diamonds with good fire will exhibit little sparks of red, green, yellow, and blue as light refracts through and out of the stone to the eye.

Brilliance is the total amount of light returned to the eye and results in the overall brightness of the stone.

Scintillation is the sparkle of the diamond and is determined by the cutting style and execution of the cut.

The quality of a diamond's cut is a complicated interaction of proportions and finishing factors. Many combinations can result in beautiful finished stones. Because the above mentioned performance elements are distinct, it is possible for the cutter to make tradeoffs in the process. For instance, making the table facet a little larger may make the stone slightly more brilliant and slightly less fiery. So while there are cut guidelines, in the end beauty is in the eye of the beholder.

Note: The word "cut" is also used in reference to a diamond's shape -- round cut, marquise cut, princess cut, etc. It is less confusing to restrict the term "cut" to a discussion of the proportions, alignment and finish of a polished diamond.

The following illustrations show the various parts of a diamond and the measurements used in the analysis of a diamond's cut:

Below is a depiction of the behavior of light entering a diamond. Well cut diamonds refract and reflect a high percentage of light back to the eye, whereas poorly cut diamonds allow light to leak out the bottom resulting in diminished brilliance and fire.

Table, Depth, Polish, and Symmetry

Depth percentage, the ratio of the total depth to the diameter, and table percentage, the ratio of the size of the large table facet to the diameter of the stone, are the most important factors affecting the overall performance of the diamond.

Additionally, two other factors in the detailing of the diamond are important in fine tuning the final product. Symmetry refers to the alignment of the facets with one another, and polish refers to the final mirror finish achieved all the facets.

Ideal, super ideal, triple o, hearts and arrows, branded and signature cuts

As if the subject of cutting was not complicated enough, now there are an ever increasing number of competing ideas about what cutting parameters are truly the best.

The concept of an "ideal" cut first gained popularity in 1919 when mathematician Gabriel Tolkowsky published a study of the behavior of light in a cut diamond and came up with a formula for proportions that would result in the most beautiful round diamond.

Over the years experimentation and scientific study have revealed that there are many proportion combinations that result in superb finished diamonds. In fact, the most important study on the subject ever conducted and utilizing advanced computer modeling technologies is the ongoing study by the Gemological Institute of America.

Despite all the hype in the trade as different companies go about promoting their own versions of "ideal" diamonds, the position of the GIA on the subject is stated in their educational materials in this way: "Unfortunately, there is no proof that any one set of proportions is truly "ideal." Preliminary results of ongoing research on cut suggest that many different proportion combinations succeed equally well."

For this reason, GIA does render qualitative cut "grades" on their reports.

To underscore how complicated the subject is, despite advanced research no definitive conclusion has been reached regarding the round brilliant cut. Fancy shapes offer a mind numbing range of different variables that may defy definitive pronouncements for generations to come!

Fancy Shapes

Diamond shapes other than round are referred to as fancy shapes. Almost any shape is possible and there are new designs coming into the market regularly as new diamond cutting technologies are developed. Determining a cut grade for fancy shapes is far more complicated than for rounds, and as a result there are no rigid standards, and therefore no "ideal" or "premium" combination of proportions. To a great extent with fancies, "beauty is in the eye of the beholder."

One of the most important aspects in fancies is the overall outline of the shape. The diamond's outline will affect the eye appeal of the stone as well as the overall design of a finished piece of jewelry. Yet this remains a relatively subjective factor.

For instance, some people might prefer a long slender marquise for a design that accentuates a long slender finger. Likewise, a pendant design might favor an elongated pear shape over one with broad shoulders.

To help you understand and visualize the outline of the stone, we have included a calculation of the length to width ratio for all our fancies on each diamond detail page. In addition, we present a representative image of a diamond with a length to width ratio similar to the diamond being viewed. By knowing the length to width ratio of the diamond in the representative image and comparing that to the ratio of the actual diamond, you are able to get a very close visualization of the outline of the actual diamond under consideration.

For example, if you are looking at a marquise shaped stone and the representative image has a ratio of 1.78, and you see in the diamond details that the actual stone has a ratio of 1.85, you know that the diamond you are considering is very slightly more elongated than the representative image. Likewise, if you are looking at an oval and the representative image is 1.45, and the actual diamond has a ratio of 1.39, you know that the stone you are considering is slightly wider than the diamond in the representative image.

We hope that you find this tool helpful in selecting the fancy shape best for your taste and best suited to the piece of jewelry that you wish to create.

Gem Diamond Company cut grades

Although there seems in fact to be no single set of parameters that are universally accepted as best, we use commonly accepted industry norms in arriving at a cut grade on our diamonds that will give customers a solid sense of quality. The values in the following tables form the basis for our dynamic cut grading system. This guidance is intended for use in conjunction with a review of the other attributes detailed in the lab report.

Round Brilliant
	Table %		Depth %
	Low	High	Low	High
Ideal	53	57	60.1	62.9
Premium	53	59	59.8	63.9
Very Good	52	60	58.0	63.9
Good	52	64	57.0	64.3
Fair	51	67	55.0	67.0
Poor	< 51	68 >	< 59	68 >

Marquise
	Table %		Depth %		Length to Width %
	Low	High	Low	High	Low	High
Very Good	51	69	54	67	1.75	2.2
Good	50	75	47	76	1.6	2.85
Fair	45	78	44	77	1.5	3.15
Poor	<44	90>	<0	43>	1.0	NA

Princess
	Table %		Depth %		Length to Width %
	Low	High	Low	High	Low	High
Very Good	59	78	64	75	1.0	1.4
Good	55	86	62	83.9	1.5	1.6
Fair	50	89	60	86.9	1.7	1.9
Poor	<49	90>	<60	87>	2.0	NA

Emerald
	Table %		Depth %		Length to Width %
	Low	High	Low	High	Low	High
Very Good	61	72	58	68	1.0	1.7
Good	60	82	56	79.9	1.8	2.0
Fair	58	86	50	83.3	2.1	2.3
Poor	<58	87>	<50	84>	2.4	NA

Pear
	Table %		Depth %		Length to Width %
	Low	High	Low	High	Low	High
Very Good	52	66	53	65	1.5	1.7
Good	51	67	50	72.9	1.35	1.85
Fair	48	69	48	75	1.2	2.05
Poor	<48	69>	<48	75>	1.0	NA

Radiant
	Table %		Depth %		Length to Width %
	Low	High	Low	High	Low	High
Very Good	61	78	59.7	73	1.0	1.6
Good	58	80	56	79.9	1.7	1.8
Fair	53	84	55	83.9	1.9	2.0
Poor	50	100	0	100	2.1	NA

Oval
	Table %		Depth %		Length to Width %
	Low	High	Low	High	Low	High
Very Good	52	63	57	65	1.5	1.7
Good	51	66	53	68.9	1.25	1.85
Fair	50	67	52	73.5	1.15	2.05
Poor	<50	67>	<52	74>	1.0	NA

Practical Advice

While a good quality round diamond with an "ideal" cut will certainly be very beautiful, very good and premium cuts might be just as attractive without costing a premium. While no commonly accepted "ideal" cut parameters exist for fancy shapes, good and very good cut grades will result in the best performance. Consider the length to width ratio of the diamond and the design of the mounting when selecting a fancy shape.