Most diamonds sold online will be "certified" which means the diamond has been sent to an independent gemology laboratory. The gem lab will put the diamond into a machine called a Sarin which precisely measures certain characteristics of the diamond such as width, length, table and girdle size as well as all of the angles created by the cutter. The diamond will then be examined by a trained gemologist and assigned color and clarity grades. It is important to remember that this step in the process is somewhat subjective as there is no machine or tool that will tell you exactly what color and clarity a diamond is.
Color is determined by comparing the diamond to be graded to a control group of diamonds whose color is known. The gemologist will then assign a color based on the closest match to the control group, as well as using his or her experience and judgement.
Clarity is determined by examining the diamond for inclusions and noting the number, location and size of the inclusions. The assignment of the clarity grade is largely determined by the gemologist's experience and interpretation of each clarity grade.
There are many gem labs in the industry, the most widely known and respected being the GIA (Gemological Institute of America). Other well known gem labs include IGI, AGSL and EGL.
Once the lab has completed the grading process, a certificate is issued describing the measurements, weight, color, clarity and other observations that were made. Most gem labs do not issue appraisals as this may be construed as a conflict of interest.
The beauty of a diamond resides not only in a favorable body color, but more importantly in its optical properties
Most commercially available diamonds are classified by color, or more appropriately, the lack of color
The clarity of a diamond is determined by the number, location and type of inclusions it contains
The weight of diamonds, and all other gemstones, is measured in carats
Table width is quoted as a percentage of the average width of the diamond's girdle
The total depth percentage is greatly responsible for the amount of brilliance that a diamond will display
The pavilion is the bottom portion of the diamond
The point on the bottom of a diamond's pavilion
Roughly one third of diamonds available in the market fluoresce
Polish is graded the same way as symmetry: Excellent, Very Good, Good, Fair or Poor on a GIA report
Symmetry is graded as Excellent, Very Good, Good, Fair or Poor on a GIA report