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When consumers are faced with a piece of jewelry, the three questions they are most interested in are “what is it”, “is it good”, and “is it worth it”. These three questions are also the three major topics of jewelry: authenticity, quality, and price. “Is it good” is the evaluation of quality. The quality is related to the price, and it is very important for buyers to be familiar with the quality evaluation of emeralds. The factors that determine the quality of emeralds are color, clarity (inclusions), brightness (transparency), cut, weight, and special optical properties.

Figure 1: A celebrity wearing emerald

Color of Emerald

Emerald stands out for its gorgeous emerald green color. Emeralds colored by vanadium and chromium have rich colors and remain green and vivid in any light source environment. They are recognized as the most beautiful color in green gemstones. For example, in jadeite, emerald green is rated as the top color. The color quality of emerald is the determining factor of its price.

Color is composed of three major elements: hue, brightness and saturation. When evaluating the color of emerald, we also start from these three aspects.

（1）Hue

Hue refers to the type of color or the appearance of a color. The purer the color of the emerald, the better the green.

Emeralds usually have a blue or yellow hue, as well as a gray hue. The increase in gray hue will reduce the quality of the color. Among the colors with yellow and blue hue, the blue hue is better than the yellow hue. This is exactly the opposite of jadeite, where the quality of jadeite is that the green with a yellow hue is higher than the blue hue.The reason why the same color hue has opposite evaluations is that jadeite shows the beauty of jade with plain jewelry. It is a collective jade that shows emerald green with reflected light.Among jewelry accessories that mainly reflect light, yellow hues give people a “sunny, pretty, and tender” feeling (the young leaves of vegetables, trees and other plants are yellow-green when they are young, and dark green or blue-green when the leaves are old, so yellow-green is called young green, and blue-green is called old green). It has a “young”, “lively” and “bright” look and feel, is popular among people, and is sold at a higher price than green with bluish hue.Emerald is a single crystal transparent gemstone. The beauty of its color is mainly expressed by transmitted light. Transmitted light needs to be clear and calm. The blue hue gives people a sense of tranquility, depth and maturity. Compared with jadeite, this hue is “dark, quiet and old”. It is this “quiet, deep and mature” feeling of emerald color that people appreciate, which is where it exudes infinite charm. It is also because of this common appreciation point of view that emerald gemstones are usually processed into “emerald cut” styles.This type of gemstone mainly highlights the transmitted light and the emerald green color, which best reflects the beauty of the emerald color. This “emerald cut” is rarely used in other gemstones. If the emerald is processed into an oval faceted brilliant cut like ruby and sapphire, the color hue will fade and the color will become lighter due to the influence of internal reflection light, the yellow hue will be enhanced and the blue hue will be weakened, which does not meet people’s aesthetic requirements for emerald color.

It should be noted that people’s preferences for color hue vary from person to person. There are differences in aesthetics between different people, and there are different appreciation standards in different periods. The above evaluation of emerald green hues is only the general view in the jewelry industry.

（2）Brightness

Brightness refers to the brightness level of gemstone’s hue. It is the sum of the intensities of all hues of light that enter the visual field from the gemstone,including transmitted light, surface reflected light, and internal reflected light. If the brightness of emerald color is too high, the color will become lighter; If the brightness is too low, the color will darken until it becomes completely black. The optimal brightness indicator for color is moderate.

Figure 2 Comparison of emeralds of different shades

(3) Saturation (color)

Saturation (color) refers to the purity and vividness of a gemstone’s color. The higher the saturation, the brighter the color, the closer it is to a pure spectral color, and the more valuable the gemstone. In emeralds, the hue usually changes slightly, the lightness does not change much, but the saturation changes greatly. The most important factor in evaluating emerald color is saturation. To measure the saturation, you can use a physical specimen or the Munsell color system to compare and determine under a standard light source. The value of emerald green varies greatly with different saturations. The price of a dark green emerald may differ by ten or even a hundred times compared to a light green emerald, and the higher the grade, the greater the price difference.

In addition, color uniformity is also very important. The more uniform the color, the higher the quality. Before observing and evaluating the color of an emerald, you should first clean the gemstone, wash and dry its surface, and observe it from different directions and under different light sources or backgrounds. This way, you can have a comprehensive and true understanding of the color of the emerald. Some laboratories evaluate and grade the color of emeralds (Figure 3).

Figure 3 Emerald Color Grading

2．Clarity

Clarity refers to the contents. It affects transparency, aesthetic appearance, and in severe cases, the durability of gemstones. The development of contents in emerald has varying degrees of impact on clarity. The factors that affect cleanliness include cracks, defects, and inclusions. The inclusion is commonly found in emerald gemstones and is usually clearly visible under a magnifying glass. Visible inclusions, other mineral particles and impurities are called defects. The more obvious these flaws are, the lower the clarity. Cracks have the greatest impact on clarity. If visible to the naked eye, cracks not only affect the beauty of gemstones, but also their durability. The cracked areas are fragile parts, and when the gem is hit or dropped, it is easy to break along these areas.

In ordinary trade, the clarity of emeralds is judged by naked eye observation. If cracks are hard to be found with naked eye, the clarity is of excellent quality. If defects are found, the nature, size, distribution, color, etc. of the defects should be analyzed. At the same time, it is necessary to realize that the development of inclusions in emeralds is universal, and perfect emeralds almost do not exist. The judgment of the clarity grade of emeralds should be compared between emeralds, rather than comparing emeralds with other types of gemstones. In short, we should have an objective understanding of the inclusions in emeralds.

Figure 4 Emeralds of different shades

3．Brightness

Emerald has a low refractive index (1.577-1.583) and weak dispersion (0.014). The fire of the gem is not its strong point. The main purpose of the emerald cutting design is to highlight its color and also to show its brightness.The brightness of emerald consists of transmitted light and partial reflected light, mainly transmitted light.Therefore, brightness is expressed as transparency. The higher the transparency, the better the brightness, and the better the transparency, the higher the quality.Transparency depends on clarity. The higher the clarity, the better the transparency. Transparency and clarity are in a positively correlated linear relationship.

It should be noted that some emeralds appear to have good clarity, but the crystals are not clear and bright enough. This is mainly because they contain tiny inclusions that make the crystals cloudy.Because the inclusions are too small to be seen by the naked eye, they sometimes do not affect the clarity grade but have a great impact on transparency.Color also affects transparency and brightness. If the color is too dark or rich, even black-green or dark green, the brightness of the gem will be reduced. For example, some emeralds produced in Zambia are darker in color and lower in brightness.In addition, cut and brightness are closely related. A poorly cut gemstone will have poor brightness.

4．Cut

The main considerations for emerald cutting are as follows: ① Showing its bright green color, releasing the darker green, and showing a brighter emerald green.② Considering the dichroic characteristics of the mineral, the parallel C-axis is blue-green, and the vertical C-axis is yellow-green, so the table of the emerald is designed to be parallel to the C-axis.③ Emerald is brittle and should not be cut with too many small facets. The curves of its shape should not be too undulating. It is easy to break during the processing and is also easy to be damaged and broken during setting and wearing, which affects the durability of the gem.For example, it is not suitable to be processed into heart-shaped, triangular and other shapes.④ Maintain weight. Minimize losses and increase the yield of gemstones.⑤ Increases the brightness of gemstones.

Figure 5 Emeralds of different cuts

Based on the above requirements, after years of exploration, craftsmen have developed a polyhedron cut with rectangular or square chamfers that is widely used in emerald processing.The four corners of the quadrilateral are cut off to become four small sides, while the crown and pavilion are faceted with long step surfaces. This typical cut is called the “emerald” cut, which is the most common and classic cut for emeralds.This kind of rectangle or square with the four sharp corners cut off makes the gem less likely to be damaged, and the rectangle or square makes the gem’s table larger.The stepped, long facets reflect incident light, increasing the brightness of the gem and bringing out the green color.The number of layers of the emerald cut ladder is generally three layers at the crown and three layers at the bottom (pavilion), for a total of six layers. Some have two layers at the crown and three layers at the bottom.

The advantage of the emerald cut is that it has a large table, which increases the transmitted light and can fully highlight its color; the disadvantage is that it has few facets and inclusions are easy to observe.Generally, gemstones with high clarity and transparent crystals are used to process emerald-shaped facets.Faceted cutting has high requirements on materials. Fine emeralds are basically faceted, especially the “emerald cut”, and the auction goods are concentrated in this cut. Raw materials with impurities, many defects and poor transparency are used to process into plain (Cabochon) gemstones.Sometimes various cuts are designed based on the shape of the raw materials.

The main cut shapes of emerald gemstones are: emerald cut and various special cuts such as cushion cut, oval cut, teardrop cut, olive cut, round cut, triangle cut, etc.Under the same quality conditions, the prices of the above cuts decrease accordingly.Some raw materials with rich inclusions and many cracks, as well as the need to produce special optical effects (starlight, trapiche), are processed into plain cabochon shapes.Some are processed into waist drum shapes, and some are even used to carve emerald jewelry into various shapes.The material requirements for plain emeralds are not high, so there are often large pieces, some of which are up to tens or hundreds of carats. Their selling price is much lower than that of faceted emeralds.The first thing to evaluate the quality of a Emerald is the shape of the Emerald. The emerald cut is considered the best shape. The symmetry of the shape, the flatness of the facets, and the quality of polishing also affect the quality of the Emerald.

5．Weight (size)

The weight of the emerald, that is, the size of the emerald, greatly affects its unit price.The unit price of faceted emerald is in geometric relationship with its weight.Especially for those weighing over 1 carat, if the weight doubles, the unit price will increase by one or even several times.This is because emerald crystals are small, with many cracks and flaws, and large faceted emeralds are rare, making them more scarce than any other gemstone.Generally speaking, goods of excellent quality over 3 carats are quite rare, and over 5 carats are even rarer.Emeralds larger than 10 carats are mostly plain emeralds. High-quality faceted emeralds are extremely rare and are considered collectible and auction-level masterpieces.