Clarity refers to how clean or clear the diamond is with respect to natural microscopic characteristics that were trapped within or on the diamond while it was forming. Internal characteristics are known as inclusions, and characteristics on the surface of the gem are known as blemishes. Inclusions may be crystals of a foreign material or structural imperfections such as tiny cracks, known as feathers, which can appear whitish or cloudy. Often times the inclusions are microscopic diamonds that were absorbed by the larger crystal before the diamond was carried to the surface of the Earth. The quantity, size, color, location, orientation, and visibility of inclusions all affect the final clarity grade of a diamond. Diamonds with no or few inclusions are considered particularly rare and highly valued.

When gemologists inspect diamonds for clarity, they use a maximum of 10x magnification and only judge the diamond face up. If an inclusion is not visible when the diamond is viewed from the top, then it cannot be used in determining the clarity grade. Gemologists use microscopes and loupes (small handheld magnifying lenses) to determine the size, type, and position of the inclusions.

Experienced graders use 10X magnification to identify the various clarity characteristics, and to map their location on “diamond plots.” These plots are like small maps for each individual diamond, and are used to identify each individual stone. No two diamonds will ever have the same internal pattern, and the plots work as a form of individual identification much like a fingerprint.

Clarity grades applied by expert graders are as follows:

• FL, IF: No internal or external flaws (FL). Flawless with no internal flaws (IF). Extremely rare and valuable.
  
• VVS1,VVS2: Very very slightly included, levels 1 and 2. Very difficult for a trained gemologist to locate under 10x magnification. Characteristics referred to as minute. VVS2 slightly more inclusions than VVS1.
  
• VS1, VS2: Very slightly included, level 1 and 2. Difficult to see inclusions under 10x magnification, unless pointed out by a trained professional. Typically can not see inclusions with the naked eye. Characteristics referred to as minor. VS2 slightly more inclusions than VS1.
• SI1: Slightly included, level 1. Inclusions are potentially identifiable under 10x magnification, but are rarely visible with the unaided eye. Characteristics referred to as noticeable. Brilliant Earth evaluates all SI1 diamonds ordered to verify that no inclusions are visible to the naked eye.
  
• SI2: Slightly included, level 2. Inclusions are easily visible under 10x magnification and may be visible with unaided eye. More inclusions than SI1. Characteristics referrerd to as noticeable or obvious. Brilliant Earth evaluates all SI2 diamonds ordered to verify that no inclusions are visible to the naked eye.
• I1 - I3: Included 1-3. Inclusions are visible to the unaided eye. Not carried by Brilliant Earth.