The color evaluation of gem-quality diamonds is based on the absence of color. Like a drop of pure water, a chemically pure and structurally perfect diamond has no hue and consequently, a higher value.
GIA's diamond grading scale is the industry's most widely accepted grading system. The scale begins with the letter D, representing a colorless diamond, and continues, with increasing presence of color, to the letter Z. The diamond’s color is established by comparing a diamond under controlled lighting and viewing conditions against a set of master stones.
Many of these color distinctions are so subtle that they are invisible to the untrained eye. These distinctions, however, make a very big difference in diamond pricing.
Natural diamonds are the result of carbon exposed to tremendous heat and pressure deep within the earth. This process can result in a variety of internal characteristics called ‘inclusions’ and external characteristics called ‘blemishes.’
Evaluating diamond clarity involves determining the quantity, size, relief, nature, and position of these characteristics, as well as how they affect the overall appearance of the stone. While no diamond is 100% pure, the closer it comes to perfection, the higher its value.
The GIA Diamond Clarity Scale has 6 categories, some of which are further divided, for a total of 11 specific grades.
Diamonds are renowned for their ability to sparkle and transmit light. We often think that diamond ‘cut’ is referring to the overall shape of the stone (round, emerald, princess, etc.), but a diamond’s cut grade is really referring to how well a diamond is faceted and how those facets interact with light.
Precise artistry and workmanship are required to fashion a stone so its proportions, symmetry, and polish deliver the magnificent return of light only possible in a diamond.
For example, to determine the cut grade of a traditional round brilliant diamond - the shape that dominates the majority of diamond jewelry - GIA calculates the proportions of those facets that influence the diamond’s face-up appearance. These proportions allow GIA to evaluate how successfully a diamond interacts with light to create desirable visual effects such as:
Brightness: Internal and external white light reflected from a diamond
Dispersion (Fire): The scattering of white light into all the colors of the rainbow
Scintillation: The amount of sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the gem.
GIA’s diamond cut grade also takes into account the design and craftsmanship of the diamond. This includes its weight relative to its diameter, girdle thickness (which affects its durability), symmetry of its facet arrangement, and the quality of polish on those facets.
The GIA Diamond Cut Scale for standard round brilliant diamonds contains five grades ranging from Excellent to Poor.
DIAMOND CARAT WEIGHT
Diamond carat weight is the measurement of how much a diamond weighs. A metric “carat” is defined as 200 milligrams.
Each carat can be subdivided into 100 ‘points.’ This allows very precise measurements to the hundredth decimal place. A jeweler may describe the weight of a diamond below one carat by its ‘points’ alone. For instance, the jeweler may refer to a diamond that weighs 0.25 carats as a ‘twenty-five pointer. Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as ‘one point oh eight carats.’
All else being equal, diamond price increases with diamond carat weight, because larger diamonds are more rare and more desirable. But two diamonds of equal carat weight can have very different values (and prices) depending on three other factors of the diamond 4Cs: Clarity, Color, and Cut.
It’s important to remember that a diamond’s value is determined using all of the 4Cs, not just carat weight.