While the vast majority of diamonds fall in the D-to-Z color range, nature occasionally produces diamonds with a naturally occurring blue, brown, pink, deep yellow or even green hue. The geological conditions required to yield these colors are rare, making diamonds with distinct and naturally occurring shades scarce and highly prized.
Unlike colorless and near-colorless diamonds, fancy-color diamonds are evaluated less for brilliance or fire and more for color intensity. Shades that are deep and distinct are rated higher than weak or pale shades.
GIA describes color in terms of hue, tone and saturation. Hue refers to the diamond's characteristic color, tone refers to the color's relative lightness or darkness and saturation refers the color's depth or strength. Using highly controlled viewing conditions and color comparators, a fancy color grader selects one of 27 hues, then describes tone and saturation with terms such as "Fancy Light," "Fancy Intense," and "Fancy Vivid." The color system GIA developed is used worldwide.
GIA offers two types of grading report for colored diamonds. The GIA Colored Diamond Grading Report contains the same comprehensive diamond 4Cs information as the GIA Diamond Grading Report, while the GIA Colored Diamond Identification and Origin Report (also known as the color-only report) is limited to color grade and the origin of the color (natural or treated).
Pearl Classification and Grading
For more than 100 years, discoveries in pearl culturing have revolutionized the market and essentially replaced natural pearls in jewelry.
A natural pearl occurs when an irritant, such as a parasite, works its way into a particular species of oyster, mussel or clam. In defense, the mollusk secretes fluid, called nacre, to coat the irritation. Over time, layers of nacre form natural pearl. In cultured pearls, the irritant is a surgically implanted bead or bit of shell.
The ability to consistently generate what was once a rare phenomenon has created a much wider audience for the appreciation and purchase of pearls. But it has also led to confusion about levels of quality and how to determine them. Cultured pearls are produced in a wide variety of colors, shapes, and sizes and grading has become proportionately complex.
In response, GIA has created a standard for describing pearl quality just as it did with diamonds. GIA's system, launched in 1998, is based on 7 Pearl Value Factors™: size, shape, color, luster, surface quality, nacre quality, and matching.
Colored Gemstone Identification
While renowned for its diamond grading expertise, GIA also receives a vast array of colored gemstones for identification. Over the decades, the Institute has created a database of information on more than 100,000 individual colored gemstones. Using this database and sophisticated analytical tools, GIA graders and researchers can pinpoint a gem's identity and, depending on the gemstone, its geographic origin. They also identify synthetics, simulants, and stones that have undergone treatment. A particularly important activity is determining whether a gemstone's color is natural or the result of a treatment process.
GIA's processes for evaluating colored stones involve multiple graders and the same item identification and tracking procedures used in diamond grading.