A gemstone or gem (also called a fine gem, jewel, or a precious or semi-precious stone) is a piece of mineral crystal, which, in cut and polished form, is used to make jewelry or other adornments.
How Gemstones are graded?
Most of the people don’t know that gemstones are graded like diamonds. Gemological institutes grades gemstones on the basis of 4c’s color, clarity, carat, and cut.
Gemstone’s color:
The Beautiful color of a gemstone is its most defining characteristic, and considers it to be the most important evaluation criterion. When deciding upon gemstone color, examine hue, tint, and saturation.
Hue: Hue is color perceived to be red, purple, yellow, green etc.., white, black and gray have no hue. Some hues like red, pink and blue are considered more valuable today than others.
Tint: A color mixed with white is a tint. A tint is lighter and less saturated than a color without the addition of the white.
Saturation: 100% of saturation means there is 0% gray in a color. Nature does not come in 100% saturation, but the higher the saturation the more expensive the gem.
Gemstone clarity:
Gemstone clarity is based the type of gemstone.
Type 1: These stones are usually eye clean, meaning that no visible inclusions can be seen with the naked eye.
Type 2: These stones are usually included, which means that some eye clean stones can be found, but in lesser amounts than type 1 stones.
Type 3: For a type 3gemstone, an IF clarity rating is incredibly rare, these stones are almost always included.
Gemstone cut:
Faceted cut and Cabochon cut are methods used in Gemstone cutting.
Cabochon Cut: The usual shape for cutting Cabochons is an ellipse. This is because the eye is less sensitive to small asymmetries an ellipse, as opposed to a uniformly round shape, such as a circle, and because the elliptical shape, combined with the dome, is attractive.
Faceted cut: Light will enter both externally and internally by a good faceted cut. This type of cut is used for transparent gemstones. This cut maximizes the brilliance of gemstone.
Like Diamonds, gemstones are cut for bring out their color richness but not for increase their brilliance.
Gemstone Carat weight: Carat weight is one of the important considerations in gemstone value. The carat weight a measure of weight used for gemstones. The carat weight was standardized in the 20th century. One carat = .2 grams or 200 grams, equal to 1/5 of a gram. Stones are measured to hundredth of a carat. A hundredth of a carat is called a point. Thus a .10 carat stone can be called either 10 points, or 1/10 of a carat.
Gemstones are graded by other parameters:
Brilliance and Depth
Brilliance: The estimated maximum of light which a stone reflects in one position under normal light conditions. High brilliancy is amongst others, the result of skilled cutting.
Depth: It is the height of a stone divided by its minimum width. The ideal range lies between 60% and 80%. It is mainly determined by the given shape of the rough stone. Under 50% a stone might be called shallow. A shallow stone with a light tone will find it difficult to maintain saturation.
Gemstone certification labs: Gemological Institute of America (GIA): GIA is considered to be the industry standard and is the most widely used and trusted name in the Diamond trade.
American gemological society (AGS): AGS is well known for its in depth scientific reach in diamond color grades. (HRD) Hoge Raad voor Diamant: Known as the Diamond High Council.
Swiss Gemological Institute: Mainly focus on perls and coloured stones certification.
International gemological Institute: Renowned for grading diamonds, colored stones, rubies. The global leader for jewelry certification.
