Of all the 4 Cs, cut has the greatest effect on a diamond's beauty. In grading, cut evaluates the cutters skill in the fashioning of the diamond.

Diamonds have a unique ability to efficiently manipulate light.  This unique ability can be realized and maximized only by cutting and polishing the diamond to an extremely high level of accuracy.  Consideration must not only be given to the proportions of a diamond, but also to the craftsmanship of its overall symmetry and polish.  A diamond's brilliance comes from light entering the top, being refracted within the stone, and then returning out the top.  A diamond that is too shallow, too thick, not finished properly , or has inefficient facet angles will leak light and not refract it as efficiently.  Such a diamond will not be as brilliant as a diamond that is a superior cut.

How a Diamond Handles Light

After more than 15 years of research and discovery, the Gemological Institute of American (GIA) has developed a scientific way to assess the cut quality in round brilliant cut diamonds.  The new cut grades, implemented on GIA certificates starting in January of 2006, range between excellent, very good, good, fair and poor.  Each cut grade represents a range of proportion sets and diamond appearances, each of which may conform in different ways to the characteristics of that grade.

GIA has calculated the cut results for 38.5 million proportion sets based on the assessment of seven components.  The first three are appearance-base aspects: Brightness, Fire, and Scintillation. The remaining four are related to a diamond's design and craftsmanship: Weight Ratio, Durability, Polish, and Symmetry.

Contrary to prior industry thinking on cut grades, including the Ideal cut diamond, the Gemological Institute of America concluded that there are many different combinations of proportions that yield excellent cut diamonds. Theare are an even wider range of proportions that are capable of providing pleasing upper-middle to middle-grade diamonds. With GIA's new system, consumers can now use cut,  along with color, clarity, and carat weight, to help them make informed and balanced decisions when assessing and purchasing round brilliant diamonds.

To locate the proportions that influence the face-up appearance of a round brilliant diamond, and to learn more about how GIA measures them, click on the link below:

http://www.diamondcut.gia.edu/05_diamond_anatomy.html

CERTIFICATES WITHOUT CUT GRADES

Round brilliant cut diamonds with GIA certificates issued before 2006 do not have cut grades. Up until that time the Ideal cut was considered the optimum cut for a round brilliant cut diamond. The GIA study concluded that many combinations of parameters yielded an equally efficient cut, and in some instances certain ideal parameters were inferior to the GIA excellent cuts. Listed below are the parameters a round brilliant cut diamond would need to receive the corresponding cut grades. The following information is no guarantee that a diamond will receive the cut grade associated with its parameters, but the information can be used as a guide. The reason for this is that the certificates issued before 2006 do not take into account some parameters such as crown and pavilion angles; although, they will be mentioned under comments if they fall beyond certain limits.

EXCELLENT CUTS FOR ROUND BRILLIANT CUT DIAMONDS
[ranges taken from a sampling of over 10,000 diamonds]

Depth... 59.1% to 62.7%    [Ideal 60% to 62.9%]
Table... 53% to 61%    [Ideal 53% to 57%]
Girdle Thickness... thin, medium or slightly thick
Symmetry... excellent or very good
Polish... excellent or very good
Culet Size... none, very small or small

VERY GOOD CUTS FOR ROUND BRILLIANT CUT DIAMONDS

Depth... 58% to 64%
Table... 52% to 63%
Girdle Thickness... very thin, thin, medium, slightly thick or thick
Symmetry... excellent, very good or good
Polish... excellent, very good or good
Culet Size... none, very small, small or medium

GOOD CUTS FOR ROUND BRILLIANT CUT DIAMONDS

Depth... 57.7% to 64.2%
Table... 55% to 66%
Girdle Thickness... extremely thin, very thin, thin, medium, slightly thick, thick or very thick
Symmetry... excellent, very good, good or fair
Polish... excellent, very good, good or fair
Culet Size... none, very small, small, medium, slightly large or large

FAIR CUTS FOR ROUND BRILLIANT CUT DIAMONDS

Depth... 55.5% to 71%
Table... 54% to 67%
Girdle Thickness... extremely thin, very thin, thin, medium, slightly thick, thick, very thick or extremely thick
Symmetry... excellent, very good, good, fair or poor
Polish... excellent, very good, good, fair or poor
Culet Size... none, very small, small, medium, slightly large, large or very large

POOR CUTS FOR ROUND BRILLIANT CUT DIAMONDS

Depth... 50.8% to 79%    [can exceed these limits]
Table... 53% to 70%    [can exceed these limits]
Girdle Thickness... extremely thin,very thin,thin, medium, slightly thick, thick, very thick or extremely thick
Symmetry... excellent, very good, good, fair or poor
Polish... excellent, very good, good, fair or poor
Culet Size... none, very small, small, medium, slightly large, large, very large or extremely large

CUT GRADE FOR OTHER THAN ROUND DIAMONDS

On the diamond results and diamond detail pages of Since1910.com, the system shows a cut grade for every diamond. The different cut grades are excellent (for round stones only), ideal, very good, good, or fair.  Each shape diamond has a different range of parameters that gives the diamond its cut grade.  The grade is determined by the depth and table percentage for the particular diamond.  Both the depth and table percentages for a particular diamond must be in the range to receive the cut grade.  Use the best cut grade that a diamond falls into as each grade encompasses a greater range.  If either the depth or table do not qualify for a particular grade, then the lower grade will be used (examples are at the very bottom of the chart below).  The ranges for each category are below:

SHAPE	DEPTH	TABLE	CUT GRADE
Pear Shape (P)	58.0 to 65.0	52 to 64	Very Good
	54.0 to 69.0	51 to 66	Good
	all others	all others	Fair
Emerald Cut (E)	58.0 to 68.0	60 to 70	Ideal
	58.0 to 70.0	54 to 72	Very Good
	56.0 to 75.0	54 to 75	Good
	all others	all others	Fair
Marquise (M)	57.0 to 65.0	52 to 63	Very Good
	54.0 to 69.0	51 to 66	Good
	all others	all others	Fair
Oval (O)	57.0 to 65.0	52 to 64	Very Good
	54.0 to 69.0	51 to 66	Good
	all others	all others	Fair
Radiant Cut (R)	60.0 to 74.0	65 to 78	Very Good
	56.0 to 77.0	63 to 80	Good
	all others	all others	Fair
Princess Cut (PR)	63.0 to 73.9	65 to 75	Ideal
	61.5 to 75.9	56 to 78	Very Good
	56.0 to 81.0	54 to 83	Good
	all others	all others	Fair
Heart Shape (H)	54.0 to 60.0	54 to 64	Very Good
	51.0 to 63.0	52 to 66	Good
	all others	all others	Fair
Cushion Cut (C)	59.0 to 69.0	53 to 60	Very Good
	56.0 to 71.0	51 to 66	Good
	all others	all others	Fair
Asscher Cut (AS)	60.0 to 69.0	53 to 68	Ideal
	58.0 to 70.0	53 to 72	Very Good
	56.0 to 75.0	53 to 75	Good
	all others	all others	Fair

Examples:

A Radiant Cut has a 62.0% depth and 79% table.  Cut = Good because the table is in the good range.  Even though its depth is very good, the table would have had to been very good as well for it to have a very good cut grade.

An Asscher Cut has a 55.5% depth and 55% table.  Cut = Fair because the depth is outside the ranges for ideal, very good and good. 

We understand picking out the perfect diamond can be tricky.  Please do not hesitate to call us and speak with a trained sales associate at 1-800-979-1910 with any questions you may have.