When buying diamond jewelry, one should appraise diamond quality based on four specific characteristics: cut, color, clarity and carat weight. Each of the 4 C's is considered when grading a diamond. Clarity is a rating of the flaws or lack thereof in a stone, including inclusions and blemishes. While judging cut or accurately grading color may be beyond an amateur eye, clarity can be fairly accurately assessed without substantial experience.
Examine with your eye
Examine the stone closely first with the unaided eye in good, preferably natural, light. Look for visible blemishes or flaws in the diamond, both on the surface (blemishes) and inside the stone (inclusions).
Use a jeweler's loupe
Look at the diamond under a jeweler's loupe to judge clarity. Most natural diamonds are slightly flawed, but good quality diamonds should have flaws visible only under magnification.
Rate clarity on a scale from flawless to imperfect. Grade stones that appear perfect to the naked eye from flawless to slightly included. Judge the degree of inclusion based on the visibility and size of the imperfections under magnification. Look at RedEnvelope's sparkling Eighty-eight Diamond Solitaire Pendant for an example of a diamond graded SL3-I1.
Rank visible flaws
Rank visible flaws as imperfect from 1 to 3. Grade flaws in the center of the cut diamond more severely than those to the side.
Care and Considerations
Use the clarity rating as one of the 4 Cs, incorporating the cut, clarity, color and carat weight of the diamond into understanding its quality and value.
Check with an experienced jeweler or gemologist for an accurate assessment of the quality and grading of a diamond. Look for diamond certifications from the Gemological Institute of America to ensure a quality stone.