After color, the next most important factor affecting the value of a colored gemstones is it’s clarity – or to be more concise a gemstone’s relative freedom from inclusions. Inclusions can affect both the appearance and durability of the gem and the clarity grade assigned to a stone is based on how visible the appearance of the inclusions are, and how much they affect the gemstone’s durability.
A Brief Introduction To Clarity Grading
Graders employ a range of five clarity grades ranging from eye clean down to severely included to classify clarity in transparent colored gemstones. However, colored stone graders do not use diamond grades to describe colored stones. Colored stones are rarely as clean as diamonds and should not be graded using the same criteria. Blemishes are confined to the surface and are not considered as a part of clarity grading. Colored stones are clarity graded without magnification.
GIA Clarity Grouping Types
Seeing as different gem minerals form from different geological processes, some gem families that are produced by some of these processes tend to have a higher disposition to be included than gem species produced by other processes.
As a result of this inequality, each gem species or variety has a range of clarity normally seen in the jewelry trade. Clarity ranges can be conveniently grouped into three Clarity Types.
Although the GIA system defines and verbalizes clarity, the definitions for slightly and moderately included stones vary and are dependent upon of the clarity type of the gemstone being graded. Basically, a Type 1 gemstone like ZOISITE (tanzanite), that is normally free of any inclusions would be graded more severely than a Type 3 stone like an emerald which is almost always included. A slightly included tanzanite could only have minute inclusions difficult to see with the unaided eye while a slightly included emerald could have noticeable inclusions apparent to the unaided eye. Both stones are slightly included but the definitions vary and are more severe for type 1 gemstones.
In this chart, species and groups appear in capital letters, varieties appear in upper and lower case letters.
Gem Type System – Type I
Stones that are often virtually inclusion free. They are so abundant in this quality that even minor inclusions detract from their desirability. Faceted Type 1 stones with eye-visible inclusions are rarely used in jewelry.
Amethyst, Aquamarine, Blue Topaz, Citrine, Kunzite, Tanzanite, Yellow Beryl, Yellow Chrysoberyl.
Gem Type System – Type II
Stones that are usually included. Stones with minor inclusions visible to the unaided eye are often faceted for use in jewelry.
Alexandrite, Andalusite, Iolite, Peridot, Rhodolite, Ruby, Sapphire, Spinel, Tourmaline, Tsavorite.
Gem Type System – Type III
Stones that are almost always included. Even specimens with obvious inclusions are faceted for use in jewelry.
Emerald, Red Beryl, Rubellite Tourmaline.
The GIA Colored Gemstone Clarity Scale
With the above principles of clairty groups in mind, the following is the GIA colored gemstone clarity scale, as according to the Gemological Institute of America.
Judging The Effects Of Clarity Characteristics
When we judge the effects of inclusions and blemishes on clarity, we need to consider the following five factors regarding the inclusions when assigning a gemstone it’s relevant clarity grade:
Consider whether the inclusion is a type that threatens a gem’s durability. Some inclusions like feathers, are potentially damaging (this also depends on their size and position).
Larger inclusions are usually more visible to the unaided eye and with certain types, more of a threat to durability. (Color, relief, and position also affect visibility.)
Color And Relief
The more an inclusion differs in color or RI from the host material, the more obvious it is, due to higher relief.
As inclusions become more numerous, they usually have a greater effect on appearance and durability. (depending on their size and visibility).
The location of an inclusion often determines how visible it is or how much it affects durability.
Typical Colored Stone Inclusions. From GIA Colored Stone Grading Manual
An opening or hole extending into the stone, usually angular in shape.
A damaged area near any edge of a stone, usually the girdle.
Any hazy or milky area that cannot be described as a feather, fingerprint, or group of included crystals or needles.
Areas or bands of concentrated or alternating colors.
A break in a stone, often with a white, feathery appearance.
Inclusions in a pattern that resembles a human fingerprint.
Visible internal evidence of the crystal growth process. Might be straight, irregular, or angular.
A mineral crystal trapped within a larger gem. Included crystals can be light or dark, transparent or opaque.
A hollow or small pocket within a gem, filled with a liquid, and sometimes also a gas bubble and a solid crystal.
A long, thin inclusion.
Oriented, fine, needle-like inclusions that can create phenomena like cat’s eyes and stars.
How To Clarity Grade
Be sure of the stones identity and determine its clarity type.
- Clean the stone thoroughly and carefully.
- View the stone face up at a comfortable viewing distance with your unaided eye, under diffused light placed about 10 in. (25cm) above the stone.
- Determine if there are any eye visible inclusions including unintended color zoning. If there are, determine how distracting they are.
- Judge the effect of the inclusions (if any) on the clarity, based on the stones beauty and anticipated durability. You should consider nature, size, number, position, and relief.
- Review the stone face up and then from all angles under 10X magnification and repeat steps 3 and 4 and try to identify any inclusions that might affect durability.
- Sum up the effects of the clarity characteristics as minute, minor, noticeable, obvious or prominent and indicate whether they have a negative or severely negative effect on appearance or durability.
Use these criteria for each clarity type to set the final clarity grade.
Despite the descriptions, clarity grading is still subjective and interpretations will show some variations even among experienced graders.