The most popular diamond shape is round, also called brilliant. But, other diamond shapes are square (princess, radiant), rectangular (emerald, baguette), oval, pear, heart, or triangle (trillion).
The Gemological Institute of America (GIA) has set standards for diamond grading based on the 4C's: cut, clarity, color, and carat (see http://gia4cs.gia.edu)
1. CUT: EXCELLENT TO POOR
Cut is considered the most important of the 4 C's and refers to facet proportions on the surface of the diamond that are cut to precise mathematical specifications.
The GIA cut quality assesses the diamond's brightness, fire, and scintillation:
Brightness - white light reflecting from both the surface and interior of a diamond.
Fire - colored flashes.
Scintillation - sparkle of light and overall pattern of bright and dark areas.
In addition, weight ratio, durability, polish and symmetry are also evaluated.
High end jewelers such as Tiffany & Co. emphasize that their diamonds are cut for beauty, not size. Tiffany points out that diamonds cut to maximize brilliance, dispersion, and scintillation usually loses size (see www.tiffany.com).
2. CLARITY: FLAWLESS (FL) TO IMPERFECT (I3)
The GIA grades diamond clarity using 10x magnification and examines the diamond for naturally occurring external blemishes or internal imperfections (inclusions) and evidence of treatments such as fracture filling or laser drilling.
Below is the GIA clarity scale examined under 10x magnification:
FL - Flawless no inclusions or blemishes are visible to a skilled grader
IF - Internally Flawless no inclusions and only minor blemishes visible to a skilled grader
VVS1 and VVS2: Very Very Slightly Included, inclusions difficult for grader to see
VS1 ad VS2: Very Slightly Included, inclusions are clearly visible, but can be characterized as minor
SI1 and SI2: Slightly Included, inclusions are noticeable to a skilled grader
I1, I2, I3 - Imperfect, inclusions are obvious and may affect transparency and brilliance
3. COLOR: D TO Z
G-H: Near Colorless
I-J: Near Colorless - A trace of tint just detectable to the trained eye
K-L-M: Faint Yellow
N-O-P-Q-R: Very Light Yellow
S-T-U-V-W-X-Y-Z: Light Yellow to Light Brown
4. CARAT: DIAMOND WEIGHT
Diamond weight is measured in carats. One carat (1.00) is equal to 0.2 grams. For small diamonds, weight is sometimes expressed in points. One carat is equal to 100 points, so a one-tenth or .10 carat diamond has 10 points.
Two diamonds of the same carat weight can vary greatly price depending on the cut, clarity, and color.
In addition, a 2.00 carat diamond will cost much more than simply twice the price of a 1.00 carat diamond.
For more information on diamond grading, see the Gemological Institute of America Guide to Understanding Diamonds and GIA Grading Reports at http://gia4cs.gia.edu
To see near perfect diamonds, go to a Tiffany & Co. store. As previously noted, Tiffany cut diamonds are maximized for brightness, fire, scintillation. In addition, Tiffany states that they only accept diamonds in the D-I color range and clarity in the top 6 out of 11 grades (VS2 or better). Tiffany also has stricter standards regarding what diamonds they accept. Tiffany lists 25 flaws that they will not tolerate. For example, they will reject diamonds with chips, black inclusions, surface inclusions, abrasions, excessive thick girdles, misshapen facets, off center table or cutlet, or table and girdle not parallel.
To see the full list of diamond flaws to look out for, go to www.tiffany.com
To learn more about the GIA (Gemological Institute of America) go to http://www.gia.edu