The 4 C's and Comparison Shopping
This is the measure of imperfections in and on the surface of the diamond. Most diamonds have natural birthmarks in various forms ~ black specks, little feather-like lines, minute bubbles and so on. As a rule, the fewer and smaller the "inclusions" and flaws, the better, since they can interfere with the passage of light through the diamond, and in some cases can also affect durability.
Diamonds are indeed the hardest substance on earth and can only be scratched by another diamond, but they are brittle and can break. That is why there is a durability risk in buying low clarity and/or poorly cut diamonds. For rings (where durability is more important), we recommend clarity grades of SI-2 (Slightly Included) or better.
At SI-2 or below, if imperfections in a particular diamond don't affect its brilliance or durability, then what you save on a lower clarity grade may be put toward a factor you consider more important ~ for example, carat-weight or cut. Again, there is no right or wrong grade--just different priorities.
Diamonds are graded for clarity under 10 power magnification. If magnification is increased above 10 power, there may be no such thing as a flawless diamond. For diamond grading, what is seen at 10 power determines the grade.
The grade "FL" or flawless is defined as nothing visible in or on the stone at 10 power. "IF" stands for Internally Flawless and means nothing is visible inside the stone at 10 power and only minor surface marks are present. The flawless diamond is rare indeed, and priced accordingly.
"VVS-1" and "VVS-2" have very, very slight inclusions that may look like a couple of very difficult-to-see specks of dust at 10 power. "VS-1" and "VS-2" have very slight inclusions that are visible under 10 power, but not large or numerous. "SI-1" and "SI-2" have slight inclusions that are easy to see under 10 power, but can't usually be seen with the unaided eye. Although not on the GIA scale, stones graded SI-3 are becoming more common, and may be considered selectively, with caution (be sure they are not really I's).
"I" means imperfect, and stones in this category will often have one or more flaws that can be seen withoutmagnification. Depending on the location and type of flaw, the beauty of an I-1 stone may or may not be affected. Although some I's are acceptable, some types of flaws allow stones to be damaged easily.
"I-2" and "I-3" diamonds are always so flawed as to affect beauty, durability or both. Even without magnification, they often look as if they are speckled with salt and pepper, or they may look like shattered ice. I-2 and I-3 stones will often have flaws near the edge (girdle). If they are hit on or near the flaw, pieces may break off (cleave). I would personally never buy either of these two grades to be mounted in a ring.
Stones graded FL through SI-1 almost always look clear to the eye. No one can tell they are flawed without the use of magnification. SI-2 and I-1 may or may not have eye-visible inclusions, depending on location of the flaws. For example, the prong of the mounting may disguise them. And some I stones, although unsuitable for rings, may have flaws which with careful cutting offer an acceptable risk if used in earrings or pendants.
Be sure to examine a variety of diamonds under 10-power magnification, to get a feel for what diamonds look like that have many, some or few flaws. Be sure the stone is cleaned before inspecting it, so no-one can explain away inclusions as "dust." In most cases, flaws are an easy grading factor for the consumer to recognize ~ you just need to look with proper equipment. Small flaws and inclusions can actually be an advantage, as they can act as a "fingerprint" to help you recognize and identify your diamond in case it is lost, stolen or switched.
When picking up your diamond from having any work done on it, or an appraisal, ask to look at it under the 10-power scope. Look first at the characteristics that tell you it's your stone, then look all around the outside edge to make sure no damage has occurred.