Emeralds are prized for their vibrant green colors. The more vivid and intense the green, the more prized the emerald. Emeralds that have sparkle, and transparency are along with a beautiful green color are the most prized.
Gemstones color is measured by three major characteristics that determine their value. Hue, tone and saturation are the elements that make up the color of a gemstone. Hue is the gradation of the color, meaning the particular tint of green that it has. Tone is the degree of absorption of light by the gemstone. This quality determines the intensity of color in an emerald. Saturation is how vivid the dominant color is in the gemstone. If the gemstone is primarily green, it carries more of a premium as opposed to an emerald that has mixtures of other colors like yellow.
The most popular emeralds are a bluish or pure deep green. This green does not have an overly dark tone. Within high quality emeralds, the color is evenly distributed throughout the gemstone. Emeralds from different mines and countries can have a differing colors as well. Emeralds from Colombia have a pure intense green color. Those from Zambia have a blueish tinged green color. However, these factors are not a guarantee of the sourcing of the gemstone. Emeralds that have a saturated and darker green are more valuable. Those that look pale or have a more icy green look are considered less valuable. In fact, those that are very light are classified as green beryl. Emeralds that do not contain more than 15% of a secondary color are considered premium and demand a much high price.
Almost all natural emeralds have eye-visible inclusions. Inclusions are tiny growths that occur within the emerald as it is forming. Emerald inclusions are often described as a garden as they have a mossy look. Emeralds that have less of these visible inclusions are more prized. The best emeralds are those that rank in the 75% range where 0% is a transparent stone and 100% is an opaque black stone. Apart from internal inclusions, emeralds are also known to have surface breaking fissures as they are a softer stone than ruby, sapphire and diamond.
Oftentimes, emeralds are heat treated to improve their color and reduce the visibility of inclusions. The majority of emeralds are heat treated. This is a permanent treatment that enhances the look of the emerald. With a combination of oil, heat and pressure the natural properties of the emerald are brought out and improved. Additional treatments are not so desirable. These treatments use resin fillers to fill the cracks and fissures of the emeralds. These can improve the look of the emerald but detract from its desirability.