Last updated on April 8, 2021
Emeralds are one of the most sought-after gemstones on the market. They are all green, but each of them varies in the shade and overall quality, making it a struggle to buy the best stone. The tips below will help you understand how to choose an emerald and get a top gem among the large variety.
Choosing Emerald Colour
Colour is the chief determinant of value when talking about emeralds. This gemstone comes in many shades of green, from medium to dark, with bluish, blue and sometimes yellowish hues.
The colour of emeralds is evaluated by three components: hue, tonal grade and saturation.
Hue describes the type of green the emerald has, for example, bluish-green, yellowish-green, etc. Tonal grade refers to the level of lightness or darkness of the green. Saturation refers to the intensity of the colour that can range from dull to pure vivid.
When choosing an emerald, it is very important to consider its tonal grade and saturation, in other words, how rich and dark is the colour of the gem. While darkness is just a matter of personal taste, colour intensity is the key, as the higher it is, the higher the value of the stone.
The most popular and valuable colour for emerald ranges from bluish-green to pure green in a medium-dark tone with strong or vivid saturation and no eye-visible colour zoning. However, it does not mean that you might not find a beautiful emerald slightly below this range.
Choosing Emerald Clarity
Clarity is important for emeralds, but inclusions are tolerated more than in any other gem. According to the Gemological Institute of America (GIA), emerald is a Type III clarity gemstone, meaning even good quality emeralds used in fine jewellery today are in I2 to I3 clarity range.
In general, the fewer inclusions an emerald has and the less visible they are, the higher the stone’s price. However, imperfections are not looked upon as negative attributes as they would be for other gemstones. In opposite, these flaws are considered part of the character of emeralds unless they have a negative effect on the transparency of the gem. In such a case, they dramatically reduce value.
Unlike diamond, emerald clarity is graded by eye. If an emerald does not have inclusions visible to the naked eye, it is considered flawless. Eye-clean emeralds are very expensive because they are rare.
Choosing Emerald Cut
As with all other gemstones, the cut of emerald refers to its faceting, shape and proportions. Cutters should consider the rough’s depth of colour, inclusions and durability to make a cutting decision. Mistakes usually cause weight loss which significantly reduces the value of a potential gem.
Almost all emeralds have significant fractures that should be designed to minimise their effect on the finished stone. Due to the fractures, emeralds are more fragile, which makes them vulnerable to damage during the cutting, polishing and setting processes. That is why the emerald cut should be designed to protect the valuable corners against damage.
Since colour is the chief determinant of emeralds’ value, the cut should maximise the hue, tone and saturation of the stone. This can be achieved by adjusting the gem’s proportions and the number of facets. Depending on the cut, the cutter can darken a light stone or lighten a dark stone. As a general rule, deeper cuts with small tables and fewer facets darken the colour, while shallow cuts with larger tables and additional facets result in lighter gems.
The emerald cut, which is also applied to other gemstones, is designed to maximise the shape of the rough and to bring out the best colour. Emeralds come in round and all fancy shapes, but these are usually expensive and rare as more rough material must be wasted to cut them.
Choosing Emerald Carat Weight
Like other gemstones, emeralds come in a wide range of sizes. The smallest sizes range from 0.02 to 0.50 carat and are usually used as accent stones. Larger gems from 1 to 5 carats are popular as centre stones. High-end jewellery pieces can include emeralds that weigh 20 carats and more.
For example, Sandawana emeralds come from an important source of superb quality gemstones Sandawana mine in Southern Zimbabwe. This mine produces highly included gems of intense colour and small size. The mine’s cut stones usually range from 0.05 to 0.25 carat and rarely weigh more than 1.50 carats. Sandawana emeralds are known for their deep, balanced, vivid green colour and a reputation for being easier to cut and polish than emeralds from other locations.
The bigger an emerald, the more expensive it is. However, keep in mind that an emerald that is twice as large as another gem of the same quality will not be twice as expensive. The price will increase dramatically because bigger emeralds are hard to find, and their rarity makes them very pricey. Besides, it is very hard to find a stone that is both top quality and large.
The vast majority of emeralds available on the market are treated to enhance their appearance. Such treatments help to improve their colour and to decrease the visibility of their inclusions, as well as make them more durable.
Since emeralds are sensitive to high temperatures, they are usually treated with oils. Jewellers traditionally used cedarwood oil because it is both colourless and has a refractive index close to emeralds.
During an oil treatment, the gem is gently heated to open its pores and filled with oil under low levels of pressure. The oil fills up tiny fissures, which helps to fade inclusions and enhance the colour.
Another type of treatment is opticon filler which is a plastic polymer resin. It is injected into gems under a vacuum. Opticon filler withstands wear and tear better and gives the stone more stability, improving its colour. However, resins can yellow and disintegrate with time.
Although the jewellery industry accepts oil and opticon treatments for emeralds, such treatments must not contain dyes as green beryl that is not green enough is not qualified as emeralds and such stones have little value in the jewellery market.