Diamond clarity is a quality of diamonds relating to the existence and visual appearance of internal characteristics of a diamond called inclusions, and surface defects called blemishes. Clarity is one of the four Cs of diamond grading, the others being carat, color, and cut. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy. The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. A clarity grade is assigned based on the overall appearance of the stone under 10x magnification.

Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. However, large clouds can affect a diamond's ability to transmit and scatter light. Large cracks close to or breaking the surface may reduce a diamond's resistance to fracture.

Diamonds with higher clarity grades are more valued, with the exceedingly rare "flawless" graded diamond fetching the highest price. Minor inclusions or blemishes are useful, as they can be used as unique identifying marks analogous to fingerprints. In addition, as synthetic diamond technology improves and distinguishing between natural and synthetic diamonds becomes more difficult, inclusions or blemishes can be used as proof of natural origin.

Inclusions and blemishes

main: Diamond flaws There are several types of inclusions and blemishes, which affect a diamond's clarity to varying degrees. Features resulting from diamond enhancement procedures, such as laser lines, are also considered inclusions and/or blemishes.

Inclusions

• Clouds
• Feathers
• Included crystals or minerals
• Knots
• Cavities
• Cleavage
• Bearding
• Internal graining

The diamond industry uses the term "internal characteristics" instead of "inclusions". For natural diamonds, the "internal characteristics" in the diamond are growth crystals that give the diamond its character and unique fingerprint. When diamonds are graded they are magnified at 10x power.

Blemishes

• Polish lines
• Grain boundaries
• Naturals
• Scratches
• Nicks
• Pits
• Chips

History

In 1952, Richard T Liddicoat, along with Lester Bensen, Joe Phillips, Robert Crowningshield and Bert Krashes began to work on a new diamond grading system which they called the diamond grading and evaluation appraisal. In 1953, they released their new system which assessed three aspects of diamonds; make, color and clarity. They took terminology used in the industry at the time and refined the definitions to produce a clarity scale by which diamonds could consistently be graded. The system at that time contained nine grades, flawless, VVS₁, VVS₂, VS₁, VS₂, SI₁, SI₂, I₁, and I₂. The I of the I₁, and I₂ grades stood for imperfect.