Unlike diamonds, gemstones may not have clear grading guidelines to distinguish their qualities. Their coloured base tone may sometimes make the reflection of light more difficult. Thus, getting a gemstone with the right colour and the right sparkle takes more than just general knowledge of gemstones and gemstone certifications. Although the cost of an emerald is influenced by its 4C profile—colour or hue, cut, clarity, carat weight and country of origin, a criterion called “crystal” or transparency should also be taken into consideration. In the grading of coloured gemstones, colour is the most important characteristic. The best emeralds are pure verdant green in hue and highly transparent.
The colour of emeralds ranges from yellow-green to blue-green, of course with a predominance of green. Yellow, blue, and red—hues adjacent to green on the colour spectrum—are the secondary hues typically found in these precious stones. Tone refers to the different shades in the emerald and indicates depth of colour; tone ranges from colourless to black. Emeralds are medium to dark in tone with a vivid hue; lighter toned stones are distinct and in the green beryl species. Saturation refers to how vivid or strong the colour is or colour purity—the degree of absence of brown or gray hues. Gray is the normal saturation modifier in emeralds; a grayish-green hue will appear dull green.
Emeralds contain many more inclusions and surface-breaking fissures than diamonds and sapphires and thus are more delicate. Unlike diamonds, these inclusions are easily visible to the human eye. For this reason, emerald clarity is graded by sight, not under magnification. So if the average person with normal vision sees no inclusions, she is looking at a flawless emerald.
The “emerald cut” was developed to accommodate the special challenges of working with these stones. Rectangular or square, the beveled corners of the emerald cut maximize the natural beauty of the stone and protect it from damage during the design process.