Diamond clarity is a quality of diamonds relating to the existence and visual appearance of internal characteristics of a diamond called inclusions, and surface defects called blemishes. Clarity is one of the four Cs of diamond grading, the others being carat, color, and cut. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy. The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. A clarity grade is assigned based on the overall appearance of the stone under 10x magnification.

Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. However, large clouds can affect a diamond's ability to transmit and scatter light, thus affecting the diamond's clarity. Large cracks close to or breaking the surface may reduce a diamond's resistance to fracture.

Diamonds with higher clarity grades are more valued, with the exceedingly rare "flawless" graded diamond clarity fetching the highest price. Minor inclusions or blemishes are useful, as they can be used as unique identifying marks analogous to fingerprints. In addition, as synthetic diamond technology improves and distinguishing between natural and synthetic diamonds becomes more difficult, inclusions or blemishes can be used as proof of natural origin.

Inclusions and blemishes

There are several types of inclusions and blemishes, which affect a diamond's clarity to varying degrees. Features resulting from diamond enhancement procedures, such as laser lines, are also considered inclusions and/or blemishes.

Inclusions

• Clouds

• Feathers

• Included crystals or minerals

• Knots

• Cavities

• Cleavage

• Bearding

• Internal graining

Blemishes

• Polish lines

• Grain boundaries

• Naturals

• Scratches

• Nicks

• Pits

Clarity grading

Gemological Institute of America (GIA)

History

In 1952, Richard T Liddicoat, along with Lester Bensen, Joe Phillips, Robert Crowningshield and Bert Krashes began to work on a new diamond grading system which they called the diamond grading and evaluation appraisal. In 1953, they released their new system which assessed three aspects of diamonds; make, color and clarity. They took terminology used in the industry at the time and refined the definitions to produce a clarity scale by which diamonds could consistently be graded. The system at that time contained nine grades, flawless, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, and I2. The I of the I1, and I2 grades stood for imperfect.

During the 1970's two changes were made to the system. Firstly, the internally flawless grade was added, as GIA noticed that many diamonds were being aggressively cut to remove any surface blemishes, and thereby reducing the cutting quality (make) of the diamonds. The internally flawless grade gave diamond manufacturers a choice to leave blemishes on the surface of the stone, and achieve a grade higher than VVS1. The second change made to the grading system, was the introduction of the I3 grade. This change was made in response to a growing number of diamonds of very low clarity being cut.

The last change to the clarity grading system took place in the 1990's when the term imperfect was updated to included.

The European Gemological Laboratory (EGL) introduced the SI3 as a clarity grade. While intended as a range to include borderline SI2 / I1 stones, it is now commonly used to mean I1's which are "eye clean", that is, which have inclusions which are not obviously visible to the naked eye.

Clarity Grading Considerations

All grades reflect the appearance to an experienced grader when viewed from above at 10x magnification, though higher magnifications and viewing from other angles are used during the grading process. The grader studies the diamond for internal characteristics, and judges them on the basis of five clarity factors; size, number, position, nature, and color or relief. The clarity grade is assessed on the basis of the most noticeable inclusions, otherwise called: grade setting inclusions. This means that less significant inclusions are ignored for the purposes of setting the grade. However, they may still be plotted onto a diamond plot chart.

Accurate clarity grading as with other grading steps must be done with the diamond loose; meaning not set into any mounting. Inclusions are often difficult to see from the crown side of the diamond, and may be concealed by the setting.

Size

The first clarity factor which is assessed is a clarity characteristic's size. Larger characteristics are typically more noticeable under magnification, thereby placing the diamond into a lower clarity grade.

Number

The second clarity factor which is assessed is the number of clarity characteristics. Generally the more characteristics the lower the clarity grade. This assessment is made by judging how readily they can be seen, not by the actual number of characteristics.

Position

The third clarity factor which is assessed is the characteristic's position. When an inclusion is directly under the table of the diamond it is most visible. An inclusion under the table and positioned close to a pavilion facet, will reflect multiple times around the stone, giving this type of inclusion the name reflector. Reflectors are graded as if each reflection were an inclusion (although in plotting the diamond it is only plotted once) . For this reason reflectors have a greater impact on the clarity grade. Inclusions become less visible when they are positioned under the crown facets, or near the girdle of the stone. These inclusions may often be more easily seen from the pavilion side of the diamond than from crown side of the diamond.

In addition the position of large feathers, knots and included crystals positioned where they extend to the girdle or crown of the stone, effect the clarity grade. Diamonds worn in jewelry typically will withstand breakage, however inclusions of this nature, in these positions, can pose a risk for further extension of the break in the structure of the diamond. Inclusions that are judged to pose at least a moderate risk of breakage to the stone are graded in the included category.

Nature

The fourth clarity factor which is assessed is a characteristic's nature. The characteristic's nature determines whether it is internal where they extend into the stone, or external; where they are limited to the surface of the stone. Internal characteristics automatically exclude the diamond from the flawless, and internally flawless categories. External characteristics exclude the diamond from the flawless category.

A diamond's internal characteristics can be a; bruise, cavity, chip, cleavage, cloud, crystal, feather, grain center, indented natural, internal graining, knot, laser drill hole, needle, pinpoint, or twinning wisp.

A diamond's external characteristics can be an; abrasion, natural, nick, pit, polish lines, polish mark, scratch, surface graining, or extra facet.

The nature will also detail whether an inclusion poses a risk to the stone. Inclusions that cause or may cause a break in the crystal structure (included crystal, feather, knot, cleavage) are considered alongside their position, to assess whether they pose a moderate level of risk for further breakage.

Color or Relief

The fifth clarity factor which is assessed is the color and relief of clarity characteristics. Characteristics that contrast with the surrounding diamond are said to have relief. The degree to which this color and relief is noticeable affects the clarity grade of the diamond. Colored inclusions invariably show contrast and are more easily seen. An exception is a black pinpoint inclusion which is often more difficult to see than a white pinpoint.

Rarity and value

Diamonds become increasingly rare when considering higher clarity gradings . Only about 20 percent of all diamonds mined have a clarity rating high enough for the diamond to be considered appropriate for use as a gemstone; the other 80 percent are relegated to industrial use. Of that top 20 percent, a significant portion contains an inclusion or inclusions that are visible to the naked eye upon close inspection. Those that do not have a visible inclusion are known as "eye-clean" and are preferred by most buyers , although visible inclusions can sometimes be hidden under the setting in a piece of jewelry. The most popular gem diamonds fall within the VS and SI grades with FL, IF, and even VVS stones commanding significant premiums , while I stones are shunned by most buyers . FL and IF stones are sometimes referred to as "museum quality" or "investment grade" to denote their rarity , although the term "investment grade" is misleading as diamonds have historically been illiquid and questionable stores of value.

Clarity enhancement

Laser "drilling" involves using a laser to burn a hole to a colored inclusion, followed by acid washing to remove the coloring agent. The clarity grade is the grade after the treatment. The treatment is considered permanent and both the GIA and AGS will issue grades for laser drilled diamonds. Reputable vendors should disclose that laser drilling has been used.

Clarity can also be "enhanced" by filling the fracture much like a car windshield crack can be treated. Such diamonds are sometimes called "fracture filled diamonds". Reputable vendors must disclose this filling and reputable filling companies use filling agents which show a flash of color, commonly orange or pink, when viewed closely. There is a significant price discount for fracture-filled diamonds. The GIA will not grade fracture-filled diamonds, in part because the treatment isn't as permanent as the diamond itself. Reputable companies often provide for repeat treatments if heat causes damage to the filling. The heat required to cause damage is that of a blowtorch used to work on settings, and it is essential to inform anyone working on a setting if the diamond is fracture-filled, so they can apply cooling agents to the diamond and use greater care while working on it.