Emerald mines Įmeralds in antiquity were mined in Egypt at locations on Mount Smaragdus since 1500 BCE, and India, and Austria since at least the 14th century CE. Others may ignore traces of oil if the presence of the material does not improve the look of the gemstone. Some gemologists consider the mere presence of oil or polymers to constitute enhancement. Laboratories apply these criteria differently. A gem graded none on the enhancement scale may still exhibit visible inclusions. These categories reflect levels of enhancement, not clarity. Gems are graded on a four-step scale none, minor, moderate and highly enhanced. Other treatments, for example the use of green-tinted oil, are not acceptable in the trade. Untreated emeralds must also be accompanied by a certificate from a licensed, independent gemology laboratory. The use of oil is traditional and largely accepted by the gem trade, although oil treated emeralds are worth much less than un-treated emeralds of similar quality. Federal Trade Commission requires the disclosure of this treatment when an oil treated emerald is sold. These treatments are typically applied in a vacuum chamber under mild heat, to open the pores of the stone and allow the fracture-filling agent to be absorbed more effectively. The least expensive emeralds are often treated with epoxy resins, which are effective for filling stones with many fractures. Other liquids, including synthetic oils and polymers with refractive indexes close to that of emeralds, such as Opticon, are also used. Cedar oil, having a similar refractive index, is often used in this widely adopted practice. Most emeralds are oiled as part of the post- lapidary process, in order to fill in surface-reaching cracks so that clarity and stability are improved. Faceted emeralds are most commonly given an oval cut, or the signature emerald cut, a rectangular cut with facets around the top edge. The relative non-uniformity motivates the cutting of emeralds in cabochon form, rather than faceted shapes. Eye-clean stones of a vivid primary green hue (as described above), with no more than 15% of any secondary hue or combination (either blue or yellow) of a medium-dark tone, command the highest prices. Imperfections are unique for each emerald and can be used to identify a particular stone. The inclusions and fissures within an emerald are sometimes described as jardin (French for garden), because of their mossy appearance. Stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated ("oiled", see below) to enhance the apparent clarity. Thus, if an emerald has no visible inclusions to the eye (assuming normal visual acuity) it is considered flawless. 10× magnification, is used to grade clarity, emeralds are graded by eye. Unlike diamonds, where the loupe standard, i.e. Įmeralds tend to have numerous inclusions and surface-breaking fissures. Clarity īrazilian emerald (grass-green variety of the mineral beryl) in a quartz-pegmatite matrix with typical hexagonal, prismatic crystals.
Gray is the normal saturation modifier or mask found in emeralds a grayish-green hue is a dull-green hue. In addition, a fine emerald will be saturated and have a hue that is bright (vivid). The finest emeralds are approximately 75% tone on a scale where 0% tone is colorless and 100% is opaque black. Only gems that are medium to dark in tone are considered emeralds light-toned gems are known instead by the species name green beryl. Yellow and blue are the normal secondary hues found in emeralds. Emeralds occur in hues ranging from yellow-green to blue-green, with the primary hue necessarily being green. In gemology, color is divided into three components: hue, saturation, and tone. In America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as " Colombian emerald". As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the UK and Europe. In the 1960s, the American jewelry industry changed the definition of emerald to include the green vanadium-bearing beryl. This member of the beryl family ranks among the traditional "big four" gems along with diamonds, rubies and sapphires. A fine emerald must possess not only a pure verdant green hue as described below, but also a high degree of transparency to be considered a top gemstone. However, in the grading of emeralds, clarity is considered a close second.
Normally, in the grading of colored gemstones, color is by far the most important criterion. Emeralds, like all colored gemstones, are graded using four basic parameters–the four Cs of connoisseurship: color, clarity, cut and carat weight.