Diamond flaws are common. Few natural diamonds are perfect; most of them have inclusions or imperfections. These inclusions are also known as flaws and exist in various forms, such as exterior and interior. Inclusions are also classified in the manner in which they were formed. For example, syngenetic diamond inclusions are inclusions which were formed while a diamond formed, while epigenetic inclusions occurred after a diamond was formed.
Flaws
The presence or absence of flaws or inclusions in a diamond is usually decided by examining the stone carefully with a lens having the standard magnifications of 10x. No other magnification should be taken as authoritative. Stones which show no apparent flaws or inclusions under this magnification are regarded as flawless. The term for a scarcely perceptible inclusion is "VVS" for "very very slight (or small)" – which is sometimes offered as flawless. Slightly larger flaws or groups of very thin inclusions are termed "VS" ("very slight"). Larger flaws or inclusions are termed as "SI" (or slightly included). Even larger flaws are termed as "1st pique". Slightly larger flaws classify the stone as "2nd pique" and so on.
Any flaws which are visible with the naked eye would be sufficient to scale the price down considerably.
External flaws
Blemishes
These diamond flaws are present on the surface of a stone and can occur naturally. However, these are more likely to be caused by the external environment when a diamond was being cut and polished.
Scratches
These are fine lines found on the surface of the diamond. They may have been present naturally or caused when a diamond was cut. While minor scratches can be removed through proper polishing, deep scratches can rarely be removed by treating the diamond.
Extra facets
These are usually cut to remove blemishes or certain close to surface inclusions on diamonds. At times these extra facets are also cut to enhance the brilliance of the diamond. These do not usually affect the clarity grade of a diamond.
Fracture
A breakage in diamonds that is not parallel to the cleavage plane is referred to as a fracture. Fractures are usually irregular in shape, making a diamond look chipped. The practice of fracture filling is commonly employed to improve the diamond clarity of such diamonds.
Fingerprints
Fingerprint inclusions in the shape of fingerprints can sometimes be found in diamonds. However, such inclusions are rare in diamonds as compared to other stones, such as rubies. Such inclusions are usually formed during fluid assisted partial healing of fractures already present in stones. For this to take place in diamonds, high temperatures and pressure (HTHP) are required, which is unusual. Few such inclusions have been reported in natural blue and colorless diamonds. While this could indicate that diamonds have been HTHP treated, giving the required temperatures for fingerprint inclusions, such is not always the case. The earth may also cause geologically high temperatures, leading to the formation of fingerprint inclusions.
Pits
Small holes may be present on the surface of a diamond. These pits are usually not visible to the naked eye. However, pits present on the table facet of a diamond are usually visible and reduce the clarity of a diamond.
Nicks
Diamonds are also chipped at places causing the appearance of nicks. This is often repaired by adding extra facets. However, too many facets reduce the brilliance of a diamond and are to be avoided.
Naturals
This refers to the original surface of the diamond, which has been left alone and unpolished. Naturals are usually left on or near the girdle of the diamond. While these are considered as blemishes, the presence of naturals is a sign of good cutting practice, where the cutter has managed to retain as much of the original weight as possible. Indented naturals are also seen to exist on some stones, where the portion of the natural is seen to dip inside slightly from the diameter of the stone. Here the cutter usually leaves the indented natural either at the girdle or pavilion of the stone, in order to keep it less noticeable. In such positions, the natural is not visible even with a loupe. Indents can be removed if the cutter polishes out more roughly. However, this would result in a drop of the diamond's weight by up to 25%.