Every diamond, like every snowflake, is unique. Diamonds differ from one another in any one of four categories, referred to as the 4C's - Carat Weight, Clarity, Color, and Cut. Using the 4C's as criteria, gemologists grade each diamond to determine its value.

CARAT WEIGHT

Carat weight is simply the weight of a diamond and does not necessarily relate to size. Diamonds are weighed in carats, and one carat is equal to 1/5 of a gram. Diamond weights can also be expressed in points or percentages. Each carat is divided into 100 points; therefore, if a diamond is described as 53 points, the weight is 53% of a carat, or just slightly more than a 1/2 carat diamond.

The diamond market has defined several different "magic weights" for diamonds, which impacts the price. A "magic weight" is the weight at which the value, or cost, per carat of the diamond increases. For example, a diamond that weighs 0.98ct can have a significantly lower cost than one that weighs 1.00ct, with all other factors equal, because 1.00ct is a "magic weight". When shopping for a loose diamond, ask for the specific weight to verify that the price is relative to the exact carat weight.

As the weight of a diamond increases, so does the price per carat.

CLARITY

To determine a diamond's clarity, gemologists view it under 10-power (10X) magnification, evaluating the diamond for inclusions. Inclusions or surface blemishes are natural "birthmarks," which most diamonds contain. The fewer and smaller the inclusions are, the less they will interfere with light passage through the diamond, and a diamond gets its beauty from how it reacts to light.

Therefore, the better the clarity, the more the value, and gemologists classify clarity using these eleven grades:

FL (Flawless)

Flawless diamonds show no blemishes or inclusions when examined by a skilled and experienced grader under 10x magnification.

The following do not disqualify a stone from the flawless category.

• An extra facet on the pavilion which cannot be seen face up.
• Naturals totally confided to the girdle, which neither thickend the girlde nor distort its outline.
• Internal graining which is not reflective, white, or colored, and does not significantly affect transparency.

IF (Internally Flawless)

IF stones show no inclusions and only signifigant blemishes under 10x magnification. normally what seperates IF from FL stones are characteristics that can be removed by minor repolishing (light surface graining is an exception).

VVS₁ and VVS₂ (Very, Very Slightly Included)

VVS diamonds contain minute inclusions that are difficult for even the skilled grader to locate under 10x magnification. In VVS₁, they are extremely difficult to see, visible only from the pavilion , or small and shallow enough to be removed by minor repolishing. In VVS₂, the minor inclusions are very difficult to see.

VS₁ and VS₂ (Very Slightly Included)

VS stones contain minor inclusions ranging from difficult (VS₁) to somewhat easy (VS₂) for a trained grader to see under 10x magnification. Small included crystals, small feathers, and distinct clouds are typical.

SI₁ and SI₂ (Slightly Included)

SI stones contain noticable inclusions which are easy (SI₁) to very easy (SI₂) to see under 10x magnification. In some SIs, inclusions can be seen with the unaided eye.

I₁, I₂ and I₃ (Imperfect)

I-grade diamonds contain inclusions which are obvious to a trained grader under 10x magnification, can often be easily seen face-up with the unaided eye, seriously affect the stone's potential durability, or are so numerous they affect transparency and brilliance.

• I₁ (Imperfect: Level 1)
  Moderate effect on beauty or durability. This is the first grade at which an inclusion can be seen with the naked eye, or without the 10x magnification. This is also the most common diamond grade found in the retail market today.
• I₂ (Imperfect: Level 2)
  Inclusions easily visible to the naked eye and has a severe effect on beauty or durability. An I₂ diamond is noticeably different from an I₁ diamond. The I₂ grade is given to a diamond that has several or very easily seen inclusions in it.
• I₃ (Included: Level 3)
  Several very visible inclusions and has a severe effect on beauty and durability. The lowest grade a diamond can receive and still be considered gem quality is I₃, after which it becomes an industrial grade diamond. An I₃ would have extremely visible inclusions. Often an I₃ diamond has inclusions that can seriously threaten the durability of a diamond.

COLOR

Diamonds are found in a range of colors - from faint yellow or brown to the very rare "fancy" colors, such as pink, blue, green, and red. Even though diamonds are available in several different colors, the most common color for diamonds is yellow, or at least some degree of yellow. The diamond color chart is considered industry standard, with "D" representing the best color grade available, or colorless. The difference between each step can be very difficult to determine, especially to an untrained eye.

The most popular color range is "Near Colorless" because diamonds in this range are more affordable, and when mounted can appear just as colorless as diamonds in the "Colorless" range. Typically, less color equals greater rarity, increasing the value of the diamond. But, the natural presence of a fancy color can result in a cost that is more than a colorless, all things being equal. An example of a fancy color diamond is the famous Hope Diamond, which is a beautiful dark blue diamond.

CUT

The cut of the diamond encompasses a diamond's style (shape and type of facet arrangement) and make (proportions and finish).

Style - Diamonds are cut into many shapes and the shape is the most recognizable attribute to most people.

Facet arrangement is a little less common. Most diamonds have one of three basic facet arrangements: brilliant, step, or mixed. Brilliant cut diamonds have a facet pattern that radiates from the center of the stone toward the edge with triangle or kite shaped facets, ex: Round Brilliant. Step cut diamonds have concentric rows of trapezoidal facets running parallel to the girdle, ex: Emerald Cut. A mixed cut diamond combines both brilliant cut facets and step cut facets; often this style is seen as a diamond with a step cut crown and a brilliant cut pavilion. Mixed cuts are not common.

Make - Whatever the shape, a well-cut diamond is the work of a master diamond cutter. When cut to good proportions, a diamond is better able to handle light, creating more scintillation, or sparkle. Although many cannot see an actual difference in cut, they can appreciate and recognize the beauty of a well-cut diamond. It is the cut that enables a diamond to make the best use of light.

How a Diamond Handles Light:

1. When a diamond is cut to good proportions, light is reflected from one facet to another and then dispersed through the top of the stone.
2. If the cut of the diamond is too deep, some light escapes through the opposite side of the pavilion.
3. If the cut is too shallow, light escapes out the pavilion walls before it can be reflected.

Anatomy of a diamond diagram