Almost all diamonds have "imperfections" in them. The clarity scale is a measure of the severity of those imperfections or "inclusions" as it is known in the trade.
Diamonds contain identifying characteristics, yet many are invisible to the naked eye. Diamonds are assigned clarity grades based on what can be detected with ten-power magnification. Most internal features (inclusions) and external features (blemishes) in the diamond have little or no effect on brilliance and fire. These are nature's birthmarks, and they may look like tiny crystals, clouds, or feathers.
Diamonds categorized as internally flawless reveal no such inclusions. Flawless stones are treasured for their rarity and beauty. Diamonds with very, very small inclusions are graded as VVS1 or VVS2. The larger the inclusion, the lower the grade and the less rare the diamond. Inclusions that can be seen with the naked eye are graded I1 or I3.
The number, color, type, size and position of surface and internal birthmarks affect a diamond's value. Major inclusions can interfere with the path of light that travels through a diamond, diminishing its brilliance and sparkle and therefore its value.
So if small clarity characteristics don't affect a diamond's beauty, why are diamonds with higher clarity grade so expensive? It's simply because diamonds with relatively few clarity characteristics are very rare. Fortunately, diamonds of all clarity grades and prices, including those with eye-visible inclusions, can look beautiful depending on how well they're cut and other factors. The best advice is to look at several diamonds of different clarity grades and let your eye be the guide!
Clarity Grade Definitions Explained