Their fiery brilliance and intense color has resulted in the popularity of gemstone jewellery. But how do you judge the quality of gemstones? Read on to learn more about the gemstone grading system.
The diamond grading system gives you an authentic report on the quality of the stone. In fact, diamonds over one carat are rarely sold without a certification. However, gemstone grading has not been as systematic or organized as diamond grading. But the scenario is gradually changing and an increasing number of international labs are now doing more and more gemstone evaluations.
Technical Knowhow on Gemstone Evaluation
Gemstone evaluation follows the same system as diamond grading. The 4Cs - color, clarity, cut and carat - are the parameters used to judge the value of a gemstone. The difference is that while the cut is the most important factor in assessing a diamond, the color of the gemstone is paramount.
Evaluating a Gemstone's Color:
A gemstone's color is evaluated using three parameters. These are hue, tint and saturation.
- Hue: This is the first impression or the perceived color of the gemstone. The color range varies through different shades of purple, red, yellow, green and blue. Some colors are more valuable than others.
- Tone: It refers to how light or dark the color of the gemstone is. Labs use 3 to denote a light tone, 5 for medium and 7 for dark.
- Saturation: It refers to the purity of the color. Hundred per cent saturation implies that the gemstone has no grey in it and the color is absolutely pure. But 100% saturation is not possible in nature. The higher the saturation percentage the higher the value of the stone. A stone with a high saturation percentage is said to have a high color grade.
How to Find a Gemstone's Clarity
Clarity refers to the extent to which a gemstone is free from flaws and blemishes. This does not play as important a role in determining the value of a gemstone as the color. The clarity of gemstones is fixed as per the following definitions:
- Type I: These are stones with no inclusions that can be spotted with the unaided eye.
- Type II: These are stones with some inclusions, but these do not detract from the overall appearance of the stone.
- Type III: These stones are severely included and these flaws can impact the appearance and durability of the gemstone.
The value of the gem will depend on the type and placement of the inclusion and its effect on the durability of the stone.
How to Find a Gemstone's Cut
Gemstones are cut using two methods - the faceted cut or the cabochon cut.
- Faceted Cut: This cut is used for transparent gemstones. A good faceted cut will reflect light both internally and externally. This will maximize the brilliance of the stone. Faceted cuts are a new innovation in the gemstone industry.
- Cabochan Cut: The cabochon cut is much easier than the faceted cuts and perhaps that is why they have been popular throughout the history of gemstones. The Cabochan cut is actually not a cut at all. It simply involves shaping and polishing the gemstone until it acquires a round top and a flat or domed base.
Again unlike diamonds, gemstones are not cut to increase their brilliance. Rather, they are cut to bring out the richness of their color.
How to Find the Carat Weight of a Gemstone
The weight measure for gemstones - except pearls and corals - is the carat. One carat equals 0.2 grams. Pearls and corals are weighed by grain or momme. One grain is equivalent to 0.25 carats and a momme equals 18.75 carats.
Other Parameters Used to Grade Gemstones
Brilliance: Brilliance of a gemstone is defined as the maximum light that a gemstone can reflect when kept under a spotlight. The brilliance of a gemstone often depends on the skill with which it is cut.
Depth: This is the ratio of the height of a stone to its minimum width. The higher value gemstones have a depth of 60 to 80 per cent. A gemstone with a depth of less than 50 per cent is considered to be shallow.
Well Known Gemstone Certification Labs
- Gemological Institute of America: The GIA is one of the most reputed labs in the business.
- International Gemological Institute: A well established independent lab.
- Hoge Raad Voor Diamant: Also known as the Diamond High Council, the body is one of the oldest gemological labs. The Antwerp World Diamond Centre plays a major role in it.
- American Gemological Laboratories
- Swiss Gemological Institute: This institute focuses mainly on certifying colored gemstones and pearls.
There was a lack of standardization as far as the terminology of the reports produced by various labs was concerned. The main gemological labs have come together to form the Laboratory Manual Standardization Committee to overcome this problem.
Different Kinds of Gemology Reports
Brief Reports: The brief report that is issued by labs provides information on weight, color, clarity, shape, size and type of the stone. Some labs will also issue a photo of the stone with the report. However, it is not mandatory to include the photo.
Standard Reports: These are sealed reports with the gemstone inside it. The information provided in these reports includes weight, color, clarity, shape, size and type of stone. There is also a comments section. Any treatment that the stone has undergone will be mentioned in the report.
Full gemstone Report: These are authenticated by the signature of the gemologist. They are comprehensive reports that give all the information provided in a standard report. Additional information includes description, proportion, finish grade, refractive index, trade name, specific gravity and a photo of the gemstone.
Buying certified and graded gemstones would mean that you have the assurance that you are buying the real thing. Certified gemstones also have greater resale value and for this reason, it is worthwhile to get your gemstone certified and graded.
