Grading of diamonds
Diamonds are graded on the basis of clarity, color, cut and carat. When graded based on clarity, they are usually checked for the absence or presence of internal inclusions or external blemishes. No diamond is 100% pure; they often contain substance other than the diamond itself. These external substances are not easily noticed with bare eyes. They can only be seen with the aid of magnifying devices. These inclusions and blemishes are mostly due to conditions under which diamonds are subjected during their formation deep down the earth. When these particles are inside the diamond, they are referred to as inclusions but when they appear externally on the body of the diamonds they are referred to as blemishes.
To grade diamonds, inclusions or blemish are checked and their shape, size, nature, position and depth are determined. Proper assessment of the clarity of diamond is very important if they must be graded accurately. According to the GIA (Gemological Institute of America) diamonds are graded into six (6) categories on the basis of clarity. They are:
- Flawless, FL
A flawless diamond is that which has no visible flaw under 10X magnification. This is the highest grade of diamonds. All things being equal, flawless diamonds are generally more expensive than other grades of diamonds. They are very rare.
- Internally flawless, IF
An internally flawless diamond is that which has no visible inclusion viewing under a magnification of 10X. There may be visible blemish, but if there are no inclusions, the diamond is graded as an internally flawless one.
- Very, very slightly included, VVS
These are diamonds with inclusions, but these inclusions are so slight that with a 10X magnification a grader might encounter difficulty grading them.
- Very slightly included, VS
Diamonds graded as ‘very slightly included’ are those with minor inclusions as viewed under a 10X magnification. These inclusions too are difficult to notice but not as difficult as the very, very slightly included ones.
- Slightly included, SI
The inclusions in these diamonds are noticeable under 10X magnification.
- Included, I
Diamonds classified as ‘included’ have very noticeable inclusions viewed with 10X magnification. These inclusions are relatively large that they may affect the transparency and brilliance of the diamonds in which they are found. All things being equal, an included diamond is the diamond with the least grade, and thus the least priced.
The different types of diamond inclusions include:
Crystals are mineral deposits found inside diamonds. They are sometimes found in clusters while some other times they appear singly. They are sometimes colored but are mostly colorless. When viewed in an overhead lighting they usually appear black irrespective of their original color.
An inclusion similar to crystal is the pin-point. Pin-point is also crystalline in structure but smaller and often whitish in color. Pin-points are almost impossible to view with 10X magnification.
A cluster of pin-point forms what is known as a cloud. A cloud can be viewed with 10X magnification.
A bruise appears as a chip on the surface of the diamond.
A chip is a flaw often created during cutting. It is noticed as a shallow nick on the surface of the diamond
These flaws are usually found on the girdle of the diamond. They are often remains of the diamond’s surface before polishing
Just like the needle used in sewing, a needle is elongated. It is an elongated inclusion.
A cavity is seen in a diamond as a depression or opening the surface of the diamond.
A feature is an inclusion looking like a feather. It is a fracture having very thin lines radiating from it. When viewed under a 10X magnification, feathers may appear white or transparent.
POWER MAGNIFICATION USED FOR DIAMOND GRADING
To see the inclusions in diamonds, which may not be noticed with the bare eyes, it is best to view them with the aid of a magnifying device. Worldwide, the standard power magnification used by gemologists for grading diamonds is 10X. Lower or higher magnifications would not give the right clarity. At higher magnifications, the flaws would be bigger. Any flaw seen at magnifications beyond 10X doesn’t count when a diamond is graded because, in standard conditions they do not matter.
When diamonds are viewed under this magnification, the size of the flaw is known as well as the position and color of the inclusion. Also, when diamonds are viewed under this magnification the blemish on their surface is also seen.
- Gemstone grading loupe
A loupe is a portable magnifying device that is used by jewelers for viewing inclusions in diamonds and other gemstones. A grading loupe is so small that it can fit into your pocket conveniently. It is also relatively inexpensive. Using a loop becomes less difficult after much practice. The most important factor to be considered when using a loop is the lighting. The grading loupe can be used to view the entire surface of a small gem, but for a big sized gem, you would have to view one part at a time.
Apart from grading gemstones based on clarity, a grading loop can also be used to grade them based on their color. A careful examination of a colored gemstone using a loupe may be able to identify gemstones with uneven color distribution.
Two very common types of 10X magnification grading loupes used by jewelers are the doublets and the triplets. Doublets are made up of 2 lenses while the triple is made up of three. These three lens elements possessed by the triplets make them improve focus better.
- The gem microscope
While the 10X grading loupe is the only device require for grading a gemstone another device that may be used to get a good view of the inclusions and other alterations in the gemstone is the gem microscope. A gem microscope has higher magnifications and can be used for taking photographs of the gemstone viewed showing the inclusions and alteration. Compared to the loupe, it is very much expensive. More skill than that required to operate a loupe is required for operating a gem microscope.
The accepted standard power magnification for grading a diamond is 10X.