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Clarity is judged by reference to inclusions. Magnification can be used to locate inclusions, but with the exception of inclusions which might impact durability, only those visible to the naked eye should influence the final grade. In this way, colored gems are very different from diamond. Indeed, in certain cases (Kashmir sapphires being a classic example), the inclusions can actually enhance beauty and value. |
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| Different levels of clarity are visible here in these spessartine garnets from Nigeria. The oval stone at left is eye clean, i.e., with no clarity defects visible to the unaided eye. In the pear-shaped middle stone, obvious clarity defects are visible, while in the trillion-shaped stone at right, they are even more obvious. Photos: Wimon Manorotkul |
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There are two key factors in judging clarity. These are:
Visibility of inclusions
- Size: Smaller inclusions are less distracting, and thus, better.
- Number: Generally, the fewer the inclusions, the better.
- Contrast: Inclusions of low contrast (compared with the gem’s RI and color) are less visible, and thus, better.
- Location: Inclusions in inconspicuous locations (i.e., near the girdle rather than directly under the table facet) affect value less. Similarly, a feather perpendicular to the table is less likely to be seen than one lying parallel to the table.
Impact on durability
- Type: Unhealed cracks may not only be unsightly, but also lower a gem’s resistance to damage. They are thus less desirable than a well-healed fracture. As already mentioned, tiny quantities of exsolved silk may actually improve a gem’s appearance, and thus, value.
- Location: A crack near the culet or corner would obviously increase the chances of breakage more than one well into the gem. Similarly, an open fracture on the crown is more likely to chip than one on the pavilion. Inclusions in certain positions may also reflect, making a single inclusion visible throughout a gem.
Note :- that cabochon-cut gems generally have poorer clarity than faceted gem. This is because inclusions are more visible in faceted stones than in cabs.
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