The grading system which they devised is comprehensive and requires some study to realize a workable understanding of the process. However, once you grasp the basic principles, you will wonder how anyone could buy a gemstone without using this kind of vocabulary. The following "walk through" of a 3.11 Burma sapphire grading report will help you understand the various components of an AGL laboratory report.
Since there are so many optical/physical principles involved in the reflection and re-reflection of light through a gemstone, any particular gem can exhibit a wide range of colors. The color grade is based upon the purity of primary color. For example, the greener the emerald, the redder the ruby, or the bluer the sapphire, the lower the numerical grade on an AGL scale. The reason the 3.11 sapphire is a 3.5 in this sample is the fact the stone has 70% blue as its primary color. It is that simple. The less primary color, the higher the numerical color grade. For example, a 65% primary color would probably be graded a 4.5 color.
In establishing a base for international quality reference standards, AGL had to be sure that all stones from the best to the worst could be accommodated by the system. Therefore, the top of the line has become almost a theoretical standard of excellence. Please do not ask for 1.00 to 2.00 color grades. Because of the AGL's stringent grading practices, a 3.5 color is usually the best color grade any gem will receive. A 3.5 colored stone on an AGL Grading Report is nearly synonymous with a D-color diamond on a GIA Diamond Grading Report. On occasion, because of our international contacts, we may find exceptional examples that will receive even better color grades.
|Very Light||Light||Light-Medium||Medium||Medium-Dark||Dark-Very Dark|
In the sample above the sapphire's tone is 75. Basically, tone describes the lightness or darkness of a gemstone. Color considered alone without taking into account the tone will lead to errors in interpretation. If a stone is too light in tone, the color will not be rich enough. Conversely, if a stone is too dark, it will sacrifice transparency and brilliancy.
|Free of Inclusions||Lightly Included||Moderately Included||Heavily Included||Excessively Included|
Clarity is defined as the degree to which the stone is free of inclusions. In the sample the clarity is MI1. Here is a good rule of thumb to remember: You will probably not see inclusions in a Lightly Included (LI) gem, you may see some inclusions in a Moderately Included (MI) gem, and you will probably see inclusions in a Heavily Included (HI) gem. Excessively Included (E) gems have durability problems and should be avoided.
The cutting of a gemstone numerically describes the overall appearance of a gem. The finish grade refers to the polish of a gem. In the sample the cutting and finish are both 3 (Very Good). These are very difficult numbers to obtain for a colored gemstone. Unlike diamonds which are cut according to strict mathematical parameters, most colored gemstones are cut for weight retention.
Some gems may receive an Estimated Commercial Acceptability (ECA) comment. (Not shown in sample.) This is usually used as a split grade. For example, a gemstone with a 4 color and an ECA of 3.5 is priced as a 3.75 color grade.
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