In January of 2006, cut grading for round diamonds has been taken to a whole new level, as this is when GIA introduced their cut grade system for round diamonds. They have taken an entirely different approach to grading cut then virtually anyone else in the industry previously. Many diamonds rated as Ideal in the industry by past standards are given lower cut grades by GIA. Conversely, many past lower cut grades are regarded higher by GIA. Will this new system be accepted by the industry? Does this new system more accurately reflect the true cut grades? The verdict on this question is still unanswered, as GIA takes many things into account that may not affect beauty. An example of this is girdle thickness.

McGiverns feels that the new GIA system will be accepted, and will become the industry standard. We also believe that this system is the best cut grading system for round diamonds. Because this system is so new, however, and because many GIA certified diamonds do not have a cut grade, we have listed details on both the new GIA Cut Grade System, as well as McGiverns previous cut grade system.

According to GIA, they have calculated the cut results for 38.5 million proportion sets based on the assessment of seven components. The first three Brightness, Fire, and Scintillation are appearance-based aspects. The remaining four Weight Ratio, Durability, Polish, and Symmetry are related to a diamond's design and craftsmanship. In the GIA Diamond Cut Grading System, each component was assessed individually, taking into account the relative importance of that component in the overall cut quality of a round brilliant diamond, and the ability of an average, experienced observer to consistently see the differences in cut quality based on these components.

GIA had been studying diamond cut for decades, when in 1989 the Institute turned a significant corner. It was at this time that new advances in computer technology allowed GIA researchers to analyze aspects of the appearance of round brilliant cut diamonds that once had been impractical and difficult to explore.

Using advanced computer modeling, we were able to replicate the way light behaves within a round brilliant cut diamond so that we could predict how a diamond would perform with regard to brightness and fire. To study these two aspects of face-up appearance, we analyzed tens of thousands of proportion sets. These proportion sets included: table size, crown angle, pavilion angle, star length, lower-half length, girdle thickness, culet size, and total depth. We also studied the effects of polish and symmetry. We found that all of these parameters were interrelated in their effects on light performance, and that no single proportion, or subset of proportions, could be considered alone. In addition, we found that there was a wide range of proportions that had the potential for high quality light performance.

For more detailed information, you can click here to go to the GIA Website.

GIA grades the cuts of Round Brilliant cut diamonds as follows:
Excellent
Very Good
Good
Fair
Poor

McGiverns recommends GOOD or better Cut based on this system. If you are really more quality driven, stick with VERY GOOD or better. If you are the ultimate perfectionist, then EXCELLENT cut grade may be the way to go.

The two prime factors in assessing quality of cut by previous standards is depth and table. Depth is the depth of the diamond divided by average diameter for rounds, Table is the large flat surface on the top of the diamond. Table is the table diameter divided by total diameter.

The numbers listed below are guidelines previously used for McGiverns ideal cuts. Keep in mind many gemologists disagreed on what made an ideal cut, and for that matter still do. Just as some art critics may like Rembrandt, others will swear by Picasso. We based our cut grading scale on a variety of cut grade systems and factors.

McGivern's previous cut grade ratings are listed below:
Ultra Ideal: Depth 58.7-62.4, Table 53-58, Polish & Symmetry Very Good or Excellent
Ideal: Depth 58.4-62.9, Table 53-60, Polish & Symmetry Very Good or Excellent
Premium: Depth 57.9-63.5, Table 53-63
Good: Depth 57.5-63.8, Table 51-64
Average: Depth 57.0-65.0, Table 51-69
Poor: Depth < 57 or > 65, Table < 51 or > 69

McGiverns has always recommended PREMIUM or better based on this system.

Just as with rounds, Quality of cut is the most important factor in determining how well a fancy shape diamond will sparkle. The two prime factors in assessing quality of cut is depth and table. Depth is the depth of the diamond by width for fancies. Table is the large flat surface on the top of the diamond. Table is the table width divided by stone width.

The numbers listed below are just guidelines for ideal cuts, or what you should look for in these numbers as you scan our database. On fancy shapes, we base our grades on a combination of systems and factors which we feel are the most accurate in presenting ideal cut guidelines.

Keep in mind on the fancy cuts, brilliance is achieved through the interaction between depth, table, and length to width ratio. For example, two pear shapes, both with identical depth and table could look remarkable different depending on length to width ratio. There is no magic formula to determine brilliance, only general guidelines. Again, we are always happy to assist in finding the diamond with the most sparkle.

McGivern recommends PREMIUM cut or better.

Princess
Ultra Ideal: Depth 64.0-75.0, Table 62-69, Polish & Symmetry Very Good or Excellent
Ideal: Depth 64.0-75.0, Table 62-74
Premium: Depth 64.0-78.0, Table 60-77
Good: Depth 58.0-80.0, Table 58-82
Average: Depth 56.1-84.0, Table 53-85
Poor: Depth < 57 or > 84, Table < 51 or > 85

Emerald & Radiant
Ultra Ideal: Depth 63.1-69.9, Table 62-69, Polish & Symmetry Very Good or Excellent
Ideal: Depth 62.0-74.9, Table 62-72
Premium: Depth 61.0-76.0, Table 60-75
Good: Depth 58.0-80.0, Table 58-79
Average: Depth 56.1-84.0, Table 53-85
Poor: Depth < 56.1 or > 84.0, Table < 53 or > 85

Asscher
Ultra Ideal: Depth 63.1-69.9, Table 55-64, Polish & Symmetry Very Good or Excellent
Ideal: Depth 62.0-73.9, Table 53-69
Premium: Depth 61.0-76.0, Table 52-75
Good: Depth 60.0-80.0, Table 51-79
Average: Depth 56.1-84.0, Table 50-85
Poor: Depth < 56.1 or > 84.0, Table < 53 or > 85

Marquise, Oval & Pear
Ultra Ideal: Depth 59.0-63.0, Table 57-60, Polish & Symmetry Very Good or Excellent
Ideal: Depth 59.0-63.0, Table 57-60
Premium: Depth 57.1-66.0, Table 53-63
Good: Depth 56.1-68.9, Table 52-66
Average: Depth 46.1-71.0, Table 51-69
Poor: Depth < 46.1 or > 71.0, Table < 51 or > 69

Heart, Trillion, Cushion & Others
No industry guidelines for ideal cut

Girdle: The outer edge of the diamond, or the widest point where the top meets the bottom, generally this will take care of itself if depth is correct. There is really no such thing as a perfect girdle, but there are certain ratings we recommend avoiding. We recommend against Extremely Thin or Extremely Thick.
F = Faceted
ET or XT or XN = Extremely Thin
VT or VN = Very Thin
T or Th or N = Thin
ST or SLT = Slightly Thin
M = Medium
(Same Apply to THICK, THK, TK and K are used as abbreviations for Thick)

Culet: The bottom, or point of the diamond. Ideally this should be None to Small.
N or NO or NN = None;
VS or VE = Very Small
S or SM = Small
M or MD or MED = Medium
L = Large

Polish & Symmetry: Generally minor cutting details of the stone, should be Good or better for both.
P = Poor
F = Fair
G or GO or GD = Good
VG or VE = Very Good
E or X or EX = Excellent

Fluorescence: Physical property of the diamond - how it appears under black UV light in a laboratory environment. In a high color diamond (D-F), fluorescence is a negative from a price perspective, ideally it should be None or Faint. In a lower color diamond, J or worse, fluorescence is a positive. Keep in mind, this is from a pricing point of view, and even though the market may view fluorescence as a negative, the simple fact is in normal lighting, in most cases fluorescence is not detectable, and does not detract from the beauty. In a small number of cases, fluorescence will make a high color diamond (D-F) appear cloudy or milky, but this the exception, not the rule. By the same token, in some cases fluorescence will make a lower color diamond, J or worse, appear whiter. If you are curious how fluorescence affect a particular diamond we have, just contact us and we will gladly offer an opinion.
N or NO or NN = None
F or FA or FNT = Faint
M or MD or ME or MED = Medium
S or STR or SB = Strong
VS or VSB or VE = Very Strong