[The Gemological Institute of America Inc. is the leading authority on diamonds and precious stones. The content of this page is taken from their site. You can find out more and get interactive scales on their site: GIA 4C's.]
Until the middle of the twentieth century, there was no agreed-upon standard by which diamonds could be judged. GIA created the first, and now globally accepted standard for describing diamonds: Color, Clarity, Cut, and Carat Weight. Today, the 4Cs of Diamond Quality is the universal method for assessing the quality of any diamond, anywhere in the world.
The 4 C's
- Color: [GIA Color Scale]
GIA's diamond 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.
Many of these color distinctions are so subtle that they are invisible to the untrained eye; however, these distinctions make a very big difference in diamond quality and price.
- Clarity: [GIA Clarity Scale]
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 Diamond Clarity Scale has 6 categories, some of which are divided, for a total of 11 specific grades:
- Internally Flawless (IF)
- Very, Very Slightly Included (VVS1 and VVS2)
- Very Slightly Included (VS1 and VS2)
- Slightly Included (SI1 and SI2)
- Included (I1, I2, and I3)
- Cut: [GIA Cut Scale]
A diamond's cut is crucial to the stone's final beauty and value. And of all the diamond 4Cs, it is the most complex and technically difficult to analyze. GIA calculates the proportions of the 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, Fire, & Scintillation.
GIA's diamond cut grade also takes into account the design and craftsmanship of the diamond, including its weight relative to its diameter, its girdle thickness (which affects its durability), the symmetry of its facet arrangement, and the quality of polish on those facets.
The GIA Diamond Cut Scale for standard round brilliant diamonds in the D-to-Z diamond color range contains 5 grades ranging from Excellent to Poor.
- Carat: [GIA Carat Scale]
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.
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.