The Gemological Institute of America (GIA) is an independent organization that set the standard for grading diamond quality around the world, known as the International Diamond Grading System™. GIA also conducts gem research and seeks to educate gem professionals.
GIA's D-to-Z color-grading scale is the industry's most widely accepted grading system. The scale begins with the letter D, representing colorless, and continues, with increasing presence of color, to the letter Z.
Natural diamonds are the result of carbon exposed to tremendous heat and pressure deep in 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 number, size, relief, nature, and position of these characteristics, as well as how these affect the overall appearance of the stone. While no diamond is perfectly pure, the closer it comes, the higher its value.
The GIA Clarity Scale has 6 categories, some of which are divided for a total of 11 specific grades.
Many inclusions and blemishes are too tiny to be seen by anyone other than a trained diamond grader. To the naked eye, a VS1 and an SI2 diamond may look exactly the same, but these diamonds are quite different in terms of overall quality. This is why expert and accurate assessment of clarity is extremely important.
Diamonds are renowned for their ability to transmit light and sparkle so intensely. We often think of a diamond's cut as shape (round, emerald, pear), but a diamond's cut grade is really about how well a diamond's 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.
The quality of cut is crucial to the diamond's final beauty and value. And of all the 4Cs, it is the most complex and technically difficult to analyze.
The GIA Cut Grading System for the standard round brilliant diamond evaluates seven components. The first three, brightness, fire, and scintillation, consider the diamond's overall face-up appearance. The remaining four, weight ratio, durability, polish, and symmetry, assess a diamond's design and craftsmanship.
Internal and external white light reflected from a diamond.
The scattering of white light into all the colors of the rainbow.
The sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond.
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 diamond price increases with 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 within the 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.