Carat is often confused with size even though it is actually a measure of weight. The cut of a diamond can make it appear much larger or smaller than its actual weight.
High carat diamonds often appear to be brighter or more brilliant than their lower carat siblings due to the prism effect of light traveling over larger distances.

One carat (not to be confused with Karat—the measure of purity of gold) is the equivalent of 200 milligrams. One carat can also be divided into 100 "points." A .75 carat diamond is the same as a 75-points or a 3/4 carat diamond.

The term carat is a derivative of the word carob. Carob seeds, which are surprisingly uniform in weight, were used as a reference for diamond weight in ancient civilizations. One carob seed equaled one carat.

It is often assumed that a 1-carat diamond costs exactly twice the price of a 1/2-carat diamond. This is not the case. Since larger diamonds are found less frequently in nature, a 1-carat diamond will cost much more than twice as much as a 1/2-carat diamond, assuming color, clarity and cut remain constant.
The most important factor when evaluating a Colored Diamond is the intensity of the color. The more intense the color, the more valuable the diamond is. The grading scale for Fancy Colored Diamonds is: "Faint", "Very Light", "Light", "Fancy Light", "Fancy", "Fancy Intense", "Fancy Deep", "Fancy Vivid".

Diamonds are also sometimes found in 'fancy' colors: pink, blue, green, yellow, brown, orange, and, very rarely, red. These diamonds, called 'fancies' are incredibly rare and valuable.

Colorless diamonds are extremely rare, and therefore very valuable. Diamonds are graded on a color scale established by the Gemological Institute of America (GIA), ranging from D (colorless) to Z.

The FancyColors extend beyond the GIA colour grading system.

Diamonds were formed under intense heat and pressure. Colorless diamonds are composed of pure carbon. Traces of other elements incorporated into their atomic structure account for the variances in color. A single change in color grade can significantly affect a diamond's value.

Cut refers to the angles and proportions a skilled craftsman creates in transforming a rough diamond into a polished diamond.

A well-cut diamond will reflect light internally from one mirror-like facet to another, dispersing it through the top of the stone. Cuts that are too deep or too shallow lose or leak light through the side or bottom, affecting the diamond's brilliance.

Cut is the only one of the 4C's that is influenced by the human hand. The rest (color, clarity, and carat) are created naturally as diamonds form in the earth.
Diamond cutting requires great skill and training. The cutter must polish tiny surfaces known as facets onto the rough diamond. This process is what creates the facets known as the crown, culet, table, girdle and pavilion of the diamond.

The facets, when arranged in precise proportions, will maximize the fire life and brilliance of a diamond. To cut a diamond perfectly, a craftsman will often need to cut away more than 50% of the rough diamond.

Cutting style is categorized into three basic types, which differ in the facets of each style:

  • Step-cut have rows of facets that resemble the steps of a staircase. The emerald and baguette are examples of this cutting style.
  • Brilliant-cut scientifically found to reflect the most light.
  • Mixed-cut have both step and brilliant-cut facets. One of the most popular types of mixed-cuts is the Princess.
    •
    		Clarity refers to the presence or absence of tiny birthmarks, or inclusions from minerals or fractures while the diamond was forming in the earth.

    When light enters a diamond, it is reflected and refracted out. If there is anything disrupting the flow of light in the diamond a proportion of the light reflected will be lost.
    Most inclusions are not visible to the naked eye unless magnified.

    Inclusions are ranked on a scale of perfection, or clarity, which ranges from FL (No visible characteristics under magnification), to I (Characteristics visible with the naked eye). This grading method rates diamonds on the size, nature and positioning of the birthmarks and requires an expert eye to assess.

    To view inclusions, trained gemologists use a magnifying loupe. This tool allows our experts to see a diamond at 10x its actual size. Even with a loupe, the birthmarks in the VVS (Very, Very Slightly Included) to VS (Very Slightly Included) range can be very difficult to find. It is only when a diamond is graded 'I' that it is possible to see the birthmarks with the naked eye.

    As with real birthmarks, inclusions appear as different shapes, such as crystals, clouds or feathers. These idiosyncrasies often add to the overall character of the diamond.