Determining the Quality of Gemstones

Purchasing coloured gemstones or gemstone jewellery is not as easy as it seems, since just like other precious metals or stones like diamonds, coloured gems also need to be bought by quality. Determining the quality of a gemstone is one of the most important things, both jewellers and customers must do before buying a gem. While there is a fixed scale to grade Diamonds on their quality, which was formulated by the GIA (Gemological Institute of America), there is no international standard for grading clarity in coloured gems.

Many buyers often get confused and thus use the four “C’s”- clarity, cut, colour and carat weight of diamond grading to define the value and quality of coloured gems. Although clarity is just as crucial in grading coloured gems as it is with diamonds, the standards are relatively different. Consumers can miss out on beautiful fine gemstones if they apply the same grading standards as diamonds to coloured gemstones. Gem dealers or jewellers often use terms like VVS and VS for grading coloured stones. However, these terms puzzle the customers as they are associated with diamond grading and therefore not really the best way to grade coloured gemstones. 

So how to be sure that the gemstone you’re purchasing is worth it’s the price? Here are some factors along with the four “C’s” that one should consider while buying a coloured gemstone. 

An essential quality factor of precious gemstones is their colour intensity, with the most valuable ones featuring a deep, concentrated colour. Colours of these gemstones varieties can vary extensively depending on the gem species. A gemstone’s colour can be intensified (or diminished) based on how it’s cut. A gemstone also goes through various treatments for colour enhancement before it is sold on the market. These include treatments like the use of high heat, dye, oil or resin infusions, surface treatments and coatings, and laser treatments.

While buying precious gems like ruby, sapphire, or emerald; here’s how to know if you’re looking at a high-quality gemstone: 

A carat (abbreviated as “ct”) is to quantify a gemstone’s weight. It is equal to 1/5th of a gram or 200 milligrams. Gem weights are commonly expressed as decimal fractions (for example - .25 carats). A carat is further divided into units known as points, and one carat is equal to 100 points. 

Some gems have diverse densities, which can affect the size per carat. For instance, when a ruby weighs more than an emerald, they both can be of one carat while the emerald will be physically larger.

Cut is not to be confused with the shape of a gemstone. Shapes define whether the stone is a rectangle, square, triangle, round, pear, marquise, and so on. The cut describes how the stone is cut into facets (from various sides). The faceting gives the gemstone its depth of colour, and its sharp edges reflect the light, giving the crystal a sparkling effect. Popular cuts include brilliant, cushion, radiant, princess, and a few more. To know more about all the fancy gem cuts, go to our guide - Popular Gemstone Cuts. 

The next essential factor for a gemstone’s quality is its clarity. It doesn’t only mean how clear the gem is. Obviously, the more transparent, the more valuable the gemstone will be. After all, who would want to buy a cloudy faded sapphire or emerald!

Clarity actually refers to the purity of a gemstone. Clarity is judged based on the evaluation of the internal and external characteristics of a gem. These characteristics comprise of the inclusions that are inside the gemstone and blemishes present on the surface. Some are flaws you can only see with a magnifier while some you can quickly see with the naked eye. The fewer inclusions or blemishes, the closer to perfection is the gemstone with a higher price.

Gems like rubies, emeralds, sapphires, all are expected to have at least some inclusions. Gems without any inclusions are scarce to find and thus are more valuable. If the inclusion is found in a place that affects the stone’s colour, brilliance, or transparency, it can significantly reduce the overall quality as well as the value of the gem.

Size also adds to the value while buying a coloured gem. Size includes the weight and face-up diameter of each type of gem material and is directly related to its value. As the size increases to that of high demand gems, the price per carat goes up. Some gemstones are rarely seen above a couple of carats, while others can weigh thousands of carats.

Also, if a gem gets beyond a size that is common for jewellery, the number of interested buyers significantly decreases, and the relative value per carat for that gem reduces. Moreover, huge gems of superior colour are always very expensive. 

As mentioned earlier, there is no such universally accepted grading system for gemstones. However, some jewellers use a particular colour grading system to grade the intensity of coloured gems like sapphires, rubies, emeralds – called the ‘A’ grading system. Grades are divided as AAAA, AAA, AA, and A.

 

• AAAA - vivid colour

• AAA - intense colour and maybe slightly included. 

• AA - deep colour and moderately to slightly included. 

• A - dark colour, look opaque, and sometimes heavily included.

Recently, GIA also introduced a clarity based grading system for coloured gems that helps buyers understand the different clarity standards for several gem varieties. There are three clarity types of gem varieties that the GIA system classifies gems into – Type 1, Type 2, and Type 3. Clarity grades in this system include the following – 

• VVS – Very, Very Slightly Included 

• VS – Very Slightly Included 

• SI1 – Slightly Included 1

• SI2 – Slightly Included 2 

• I1 – Included 1 

• I2 – Included 2 

• I3 – Included 3 

To further understand this system, check out our guide on – Gemstone Grading Systems.

So now you will have some idea about the quality of a coloured gemstone while buying it. If you’re still not sure about the quality of the gem you are purchasing, then you can also consult a reputable jeweller who can assist you in selecting the highest quality gemstone within your budget.