We all wish for a perfect diamond, but nature isn't so generous and those diamonds are very, very rare. The extreme pressures and temperatures under which diamonds are formed will almost always create a stone with some internal or external flaw.
Such defects may include air bubbles, foreign material, or feathers, but these are most often microscopic flaws. Gemologists in a laboratory, using 10X magnification, study each stone, and nearly every diamond will contain some defect that nature has included when forming the stone. The location and size of the flaw is important and noted as well, and make each diamond unique.
When a stone, even when examined under magnification by a trained gemologist, reveals no internal flaws, the diamond is graded IF, or internally flawless. Such magnificent stones are so rare that most of us will go our entire life and never see one. Stones in the next grade of clarity, VVS, are said to be very, very slightly included. While these stones do have internal or external imperfections, the blemishes are very difficult to locate, even under magnification.
If the inclusions or external blemishes are difficult to locate, the stones are graded VS and these are more common than either of the higher grades. A VS grade diamond still has no defects that you can see with your naked eye, and the average person would never notice them.
If the inclusions are easy to locate under magnification, the stone is graded SI1, or slightly included. Again, to the untrained eye it is hard to spot the inclusions in stones of this grade, and they can still produce plenty of sparkle! SI2 or SI3 graded diamonds can have some inclusions slightly visible to the naked eye but they are very slight and don't affect the beauty or brilliance of the diamond.
A stone that has medium or large blemishes that are normally very visible to the trained eye under magnification, or even to the naked eye under the right light, is graded included, or simply I. Some consider a stone in this grade to have "character," and while not perfect they can still display a great deal of fire and brilliance.
Learn how your diamond’s shape and cut can affect its brilliance.
About diamond cut
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About diamond color
Nearly all diamonds have various natural marks. Learn how a diamond’s clarity is graded.
About diamond Clarity
Simply the weight of the stone itself, without the setting. Not all diamonds have the same price for the same weight.
About diamond Carat Weight