How to pick the best diamond, Diamond Education

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The 4 C’s of Diamonds

Cut-  The single most important factor of a diamond’s brilliance.  Since 1929 gem cutters began cutting diamonds with 58 facets which is the traditional cut and has proven to be the most popular cut in today’s market.  The first facet is the table. The crown has 32 facets, the pavilion has 24 facets and the culet is also a facet.  The table should be approximately 60% of the diameter of the girdle.  The girdle diameter is always considered 100%.  For example, a well cut one carat round diamond measured by its girdle is 6.5 mm and the table should be approximately 60% of 6.5 mm or 3.9 mm.  Depth is also vital in choosing a well cut stone.  Depth is measured from the top of the table to the bottom of the culet in mm.  A well cut round diamond has a depth of approximately 60% of the diameter of the girdle.  Other shapes such as princess, ascher, radiant, emerald and cushion diamonds can vary approximately 10% higher on table and depth.  For example, when choosing these shapes a 70% ratio for table and depth are best for brilliance.  The shapes mentioned above are closer to the shape of a rough diamond (octahedron) and therefore waste is minimized during the cutting process.  When comparing a one carat round diamond to a one carat princess cut diamond of the same quality, the princess cut will be less expensive. 

The polish of a diamond is the finishing stage in enhancing the brilliance of the stone.  The girdle of a diamond should be polished and faceted.  Polish on the girdle is often overlooked on non-certified stones.  A non-polished girdle appears as a frosted line that separates the crown from the pavilion.  The girdle thickness of a diamond should be medium to slightly thick.  A girdle that is cut too thin can be damaged or chipped from every day wear.  A thick girdle is the result of a poorly cut stone by gem cutters who attempt to achieve a higher carat weight diamond which could bring more revenue.  These stone often have setting problems and may not remain secure in the mounting.  All certified diamonds have a polish and symmetry grade in the report.  GIA certified stones clearly state the polish and symmetry grade as Excellent (EX), Very Good (VG), Good (G), Fair (F) and Poor (P).

Symmetry refers to the cut of the stone.  A perfectly symmetrical stone will reflect light to achieve maximum brilliance.  A symmetrical stone has properly aligned facets and a culet that is aligned with the center of the table when viewed from the side.

Chart is consistent with GIA cut grade scale.  Cut grades are Excellent, Very Good, Good, Fair and Poor.

Carat Weight- Historically the word carat is derived from carob.  A bean produced from a Mediterranean tree which had consistent weights each year.  Carob beans were used as a unit of measure for weighing diamonds.  Thus, the carob evolved into the word carat, which is the unit we now use to measure the weight of diamonds and other gemstones.  Diamond carat weight is broken down into points, for example there are 100 points in a 1 carat stone, 50 points in a ½ carat stone, 25 points in a ¼ carat stone, etc…It is important to know the exact carat weight of your stone.  There can be a significant difference in price between a 99 point and a 1 carat diamond when color and clarity are equal.  Since carat weight is equivalent to color, clarity and cut combined it is essential to understand how carat weight can change the price of a diamond.  Retail stores can legally round up your 0.95 to a 1.00 ct diamond , the chart below indicated that a 95 pt diamond falls in a different per carat price than that of a one carat. 

Chart 1.  Price per carat changes according to the points in the chart above.

Color-  Diamonds are color graded on their side and not from the top.  Certified stones are always graded loose before they are mounted.  A yellow mounting can influence the color of the stone.  Fancy yellow diamonds should be purchased with certification from a reputable laboratory.  K-Z are considerably less in price and should not be mistaken for a fancy yellow diamond.  Fancy yellow colored diamonds will come with a color description such as “Vivid Yellow”, “Fancy Intense Yellow”, etc… in the certification.

Fluorescence is a test performed under black light and is noted in the certification.  The most common flourecence is blue.  The intensity of the fluorescence is listed on the certification as faint, slight, moderate, medium and strong.  A faint or slight blue fluorescence should not prevent the purchase of a diamond.  Moderate, medium and strong fluorescence can appear hazy or milky.  Fluorescence is more noticeable on colorless stones.  Slightly yellow stones (J color and below) may appear whiter with a blue fluorescence.  Fluorescent stones hold less value and do not enhance the brilliance of a diamond, therefore the most valuable diamonds are colorless and non-fluorescent. 

Clarity-  Clarity is a unit of measure that describes the natural inclusions found in a diamond.   It is the most subjective of the 4 C’s.  Choosing a higher clarity grade is more expensive than choosing a higher color grade.  Diamonds of clarity grade below SI2 are imperfect.  These imperfections can be seen with out magnification and are significantly less in price. Best Value-VS1-SI2. 

Types of inclusions seen in clarity grading:  Pinpoint, Feather, cloud, carbon. 

Diamond Certification- There are three respected laboratories in the industry, they are  AGS (American Gem Society), GIA (Gemological Institute of America) and EGL (European Gemological Laboratory).   All laboratory certifications are performed by a panel of three judges using a jeweler’s loupe (10X) and may not correlate with each other.

AGS grades their diamonds on a scale from 0 to 10.  Zero being the highest grade or the most desirable grade for cut, color and clarity. 

GIA certifications are the most recognized in the diamond industry, they follow the alphabet D through Z for color grading and Flawless to Imperfect for Clarity.  Cut specifications are as seen under the Cut portion of the 4 C’s in the education page.  

EGL certifications follow the GIA grading specifications for the 4 C’s.  Although they are based in Europe there are two labs in the U.S.A., California and New York.