Feathers
Feathers refer to the small cracks in the diamond. The location of these feathers affects the durability of the stone. If feathers are present at the top of the diamond prove to threaten the diamond structure; since the top is more prone to accidents.
Cleavage
A straight crack with one feathering makes for a diamond cleavage. It affects the diamond’s build, as a presence of a cleavage can crack the stone into two pieces. However the minute cracks that are not conspicuous may not affect the diamond’s build directly.
Girdle Fringes or Bearding
Girdle fringes, as the name suggests are the hair-like streaks that appear around the girdle. Also known as breading, they are the result of the cutting process. Negligible bearding might not devaluate the diamond quality, but the extensive fringing should be removed or refined away by cutting the diamond again.
Chip
A chip is a mark or flaw located on the surface of the diamond due to the breaking off or gouging out of a small piece. Commonly, since most chips are minor they can be removed from the diamond surface, by re-cutting or polishing the gem with a negligible loss of weight.  However, the bigger chips may require that the entire diamond be re-cut resulting in a more substantial loss of diamond weight, at times one-third to a half of the carat weight or more.
Included Crystals and Mineral Inclusions
Some diamonds have minute crystals and minerals engrafted in them. The crystals are actually often the smaller diamonds trapped inside the bigger diamond. Higher magnification and proper lighting can make you see the boundary between the knot and the diamond which contains it. These external bodies obstruct the flow of light- dispersion and refraction. Diamonds with such inclusions have lower clarity grade and value.
Knots
Knots are those included diamond crystals that extend to the surface of the diamond.  In other words, it is a diamond crystal which reaches the polished surface of a finished diamond.  Under magnification knots sometimes appear like raised areas on a facet surface.  Knots not only spoil the beauty of the diamond but may also threaten the potential life of the diamond. 
Cloud or Pinpoint Inclusions
These are the petite-light or murkier crystals that are present in diamonds singularly or in clusters. The bigger clusters of minute pinpoints will result in some blurry cloud like area in the diamond. An ugly spot on the diamonds their presence depreciates the diamond’s clarity and value.
Internal Graining -Grain /Growth Lines
Grain lines are formed during the origination of the diamonds. They are the result of irregular crystallization and do not affect the diamond clarity unless present in huge clusters. The grain lines with color tinges can lower the diamond’s clarity grade.
Laser Lines
The laser lines are not natural occurrence; these are the marks left behind by the laser in process of eliminating the dark inclusions present in the diamond. These lines look like miniature fibrils that stretch all the way inward from the diamond’s table.

The blemishes occurring on the diamond’s surface are of several types. Some blemishes occur naturally while others are the outcome of the cutting, polishing or other frictions.
A surface blemish deprecates the diamond value and price although they might not be very noticeable.
Nicks
Nicks are the locations on the diamond where a miniscule fraction has a chipped away. An extra facet can be created by polishing the minute nicks. But again the more new facets created depreciates the diamond’s value and appearance.
Pits
Pits are the small holes present on the diamond’s facets. Few are not conspicuous but they will affect the brilliance and clarity’s grade. Shallow pits can be fixed by polishing.
Scratches
Scratches are small fine lines present in the diamond’s surface. They may be a result of the mining process and can be easily polished off. The diamond is set in a jewelry ensemble needs to be detached before polishing.
 Natural
A natural refers to that area of the diamond that is left unpolished. Diamonds are often left unpolished at the girdle deliberately to add to the carat weight of the diamond. They do not devaluate the diamond’s clarity grade if located only on the girdle.
 Trigon
A trigon is a natural that looks like a small triangle. They might appear as series of triangles within triangles.
Twinning Wisps (Intergrowth)
Twinning Wisps describe the formation of inclusions which have twisted together within a twinning plane. They are also known as Intergrowth. Such a formation might be a combination of variety of inclusions such as pinpoint size diamond crystals, fractures, crystals, feathers and clouds. Brilliant Cut Round diamonds generally never have this flaw.
Polish lines
Polish lines are the marks that may crop up during the cutting and polishing of the diamond. They downgrade the diamond’s value and clarity. Polishing lines located on the pavilion compared to other areas are not as conspicuous as on the table facet.  

Size of the flaw
The size of the flaw is crucial in evaluating the clarity grade as well as value of the diamond. Larger the flaw present in the diamond more it steeps down in its clarity grade. The bigger flaw not has more chances of being visible, hampering the brilliance but is also equally difficult to hide.
Number
The clarity grading is also assessed by the number of flaws present in the diamond. The more the less the clarity, brilliance and value of the diamond, more so if they are visible. Since the diamonds are valued for their crystal clear look, the higher number of flaws kills its aura.
 Position
The position where the flaw is situated largely affects the clarity grading, value and life of the diamond. The internal flaws present under the table and close to the pavilion facet are named reflect. These reflectors have a direct outcome on the diamond clarity grade. Inclusions are less conspicuous when they are positioned under the crown facets or close to the girdle of the stone. Inclusions located at certain crucial areas might even cause the diamond to break.
Nature
The nature of the flaw-internal or external, determines its value and the possibility of correction. Certain internal flaws may not be visible to the naked eyes or be hidden by cutting and metal setting. Even the minor surface flaws be corrected by polishing, without causing much impact on value. The nature will also throw light on the inclusions that might threaten the anatomy of the stone.
Color or relief
The amount to which color or relief of the inclusions are noticeable, determines the clarity grade of the diamond. Relief refers to the contrasting characteristics that contrasts the surroundings of the diamond. Colored inclusions show contrast and more easily visible. Though an exception, strikingly black pinpoints are less evident compared to white pinpoints.

Diamond clarity largely influences the diamonds value and brilliance. The flaw may or may not be visible to the naked eyes. Gemologist use 10X loupe magnification to evaluate the diamond grade. The grading is based on the industry standards, benchmarked by the Gemological Institute of America (GIA). The most reputed laboratory they have scaled eleven different grades in six categories, to evaluate the diamond’s clarity.
In 1952 a team of gemologist lead by Richard T Liddicoat started working on the diamond grading system, with only nine clarity grades. They defined- flawless, VVS1, VVS2, VS1, VS2, SI1, SI2, I1 and I2, where I in I1 and I2 grades stood for word Imperfect. Then latter in 1970s two changes were made to the system. Internally Flawless (IF) grade were added- as GIA realized that diamonds were precariously cut, adding to the blemishes. The second change was the origination of the I3 grade. Rising number of low clarity diamonds gave birth to this alteration. The last modification took place in 1990s when term ‘Imperfect’ was updated to, ‘Included’.

The GIA grading scale is as follows:-

Different organizations grade the diamond clarity by subjecting the diamond to 10x magnification. Their skilled professional study the diamond characteristic, under special environment and lighting. However, the grading scales are usually the same, with minor additions or variations.  
American Gem Society- Diamond Grading Scale

The American Gem Society (AGS) ranks diamond clarity on a number scale between 0 and 10. These numbers grades are virtually correlative with the GIA system, but with some minor changes. One of the most respected labs, they have clubbed the Flawless (FL) and Internally Flawless (IF) represented in the (0) grade with notation specifying if the stone is clear of external blemishes, the VVS through SI grades are numerated 1 through 6, and then there are four grades 7 through 10 for the category.

International Diamond Council (IDC) - Diamond Grading Scale

Gemologists and grading labs use different processes and standards to evaluate the diamond grade. GIA uses 10X magnification with darkfield illumination to determine the diamond clarity and its grading. The grading is executed using 10x handheld loupe under ultraviolet light, filtered with overhead light. The light-source is used to illuminate the base of the stone and crown of the stone concealed from the light. After carefully cleaning the diamond, the latter is lifted with tweezers. The inclusions in the diamond are studied from the pavilion side as well as the crown side of the stone, scanning through each facet.  If the grader is using a stereo microscope, he can zoom in to a higher magnification to make closer observations of an inclusion. He needs to again zoom out, back to 10x magnification to make a judgment of its impact on the clarity.
10X diamond grading loupe is the standard equipment used for the diamond grading.  It is the basic degree of magnification to should rely on when evaluating a diamond for purchase. The higher magnifying equipments like 20X, 30x to 70X, may show more inclusions which may not be as clear under the 10X industry standards. Since no diamond is perfect, it is possible that even a Flawless (FL) diamond may show some inclusions under higher magnification.

Diamonds that have highest clarity are few and far between. Merely 20 percent of the total diamonds mined posses the clarity rating that would ensure their use as a gemstone, remaining 80 percent are submitted to industrial use. Of that 20 percent a substantial lot contains inclusions and/or blemishes conspicuous even to the unaided eyes. Only one-fourth of the gem-quality diamonds can be graded Flawless under 10X loupe. Consequently, those that are visibly flawless are greatly desired in the market. The subsequent rarity against the high demand and diamond aesthetic value makes it an extremely valuable treasure. In fact, the diamonds that fall within the VS and SI grades with FL, IF and VVS; the FL and IF diamonds are also known as ‘museum quality’ or ‘investment grade’.

The market is filled with diamonds that do not approve the GIA standards and use unlawful treatments to enhance the diamond clarity. Ensure that you too do not end up being cheated paying more for a diamond that is even below the acceptable standards. It is therefore advised to always buy a diamond from a reputed jewelry store like MySolitaire.

The popular practices for clarity enhancement of the diamonds include-
Laser Treatments
The laser can be used to remove the inclusions present in the diamond. An experienced gemologist can however detect the laser marking. This treatment often affects the florescence of the diamond. The changes left behind by the laser are permanent. The diamond’s clarity is enhanced by laser “drilling” that employs laser to burn a hole to a colored inclusion succeeded by acid washing to remove the coloring agent. MySolitaire does not offer such diamonds.  
Diamond Fracture Filling
Minute cracks in the diamond are filled with colorless substance.  This is an unlawful practice with temporary results. Clarity can be improved by filling the diamond. These diamonds aka fracture filled diamonds shows some color tinge commonly orange, pink.
In fact, certain genuine renowned companies often facilitate repeat treatments if the heat ruptures the filling. MySolitaire does not offer such diamonds.
These clarity enhancement is not approved by the GIA, nor do they grade fracture-filled diamond. If the GIA diamonds that have notification of "clarity enhanced" or "fracture-filled," it is a fake report. MySolitaire offers only those loose diamonds that have been graded by GIA.