Colored Stone Grading - Clarity
Clarity Grade: Unlike diamonds, colored gems are clarity graded under the GIA system by the naked eye rather than at 10x magnification. We use a standard overhead daylight fluorescent grading light, with the gem held approximately 10 inches from the eye. Some experts, including the GemGuide folks, recommend additional examination of the stone using 10x magnification, and then noting the magnification findings along with the eye grade. For the more expensive stones, such as fine and extra fine grades of ruby, this approach makes certainly makes sense. For more general use, the GIA standard is adequate in most cases.
We begin with the clarity terms of the GIA colored stone grading system. While the terms are somewhat similar to those used in GIA's diamond grading system, it really is like comparing apples to oranges.
- Eye Clean = approximately equivalent to Flawless grades for diamond
- Slightly Included = approximately equivalent to VVS/VS
- Moderately Included = approximately equivalent to SI
- Heavily Included = approximately equivalent to Included, level 1
- Severely Included = approximately equivalent to Included, level 2 or 3
Additionally, because natural processes of formation are unique to each gem type (and location), the same clarity standards cannot be applied like a blanket to all the colored stones. Thus, an emerald cannot be clarity graded to the same standard as its cousins: aquamarine, morganite, or other beryls. It’s not fair to the material and doesn’t reflect reality. GIA has developed a classification of clarity type, so that the different gem varieties can be graded relative to the way they form in nature. This classification applies to transparent gems only. The primary gems are placed in 3 Clarity Types as follows:
- Type 1: Aquamarine, Morganite, Green Beryl, Heliodor, Chrysoberyl, Spodumene (Kunzite), Blue Topaz, Green Tourmaline, Blue Zircon, Colorless Zircon, and Tanzanite
- Type 2: Andalusite, Apatite, Alexandrite, Corundum (Ruby, Sapphire), Diopside, Feldspar (Moonstone, Sunstone), Garnet, Iolite, Fire Opal, Peridot, Quartz, Spinel, Imperial and Precious Topaz, Tourmaline other than green, and Zircon other than Blue or Colorless
- Type 3: Emerald, Red Beryl, and Watermelon Tourmaline
The GIA clarity grading relates to the Gem Guide scale of 1-10 in the following matrix, as seen in The Gem Guide Color price book, Fall/Winter 2008-2009. p. 7.
The main differences between grading the clarity types are seen mainly in the Good 4-6 and Fine 6-8 ranges. For example, an aquamarine (type 1) must have only minute inclusions, barely visible with the unaided eye, to be in the Slightly included Fine 6-8 range. Its cousin, the emerald, could have noticeable inclusions apparent to the naked eye and still be considered Slightly included Fine 6-8. All types must be eye clean to be considered Extra Fine 8-10, and all types that are heavily or severely included can be no higher than 3-4.
Thus, our grading for clarity will be as follows, with appropriate clarity type designation:10 - Eye Clean, loupe clean
9 - Eye Clean, minute inclusions visible at 10x
8 - Eye Clean, minor inclusions visible at 10x
8 - Slightly Included
7 - Slightly Included
6 - Slightly Included
6 - Moderately Included
5 - Moderately Included
4 - Moderately Included
4 - Heavily Included
3 - Heavily Included
2 - Severely Included
1 - Severely Included