Addendum Colored Stones

COLORED STONE GRADING NOMENCLATURE

Color is described by three components hue, tone, and saturations. Hue is the dominant color and any additional colors visible in a stone. Examples are orangey red or bluish green. Tone is the lightness or darkness of the color from the colorless to black. Saturation is the strength of the color from grayish or brownish to vivid.

Clarity for colored stones will be graded by the same nomenclature as diamonds (FL, VVS, VS, etc.). However, some colored stones naturally grow with more inclusions. Therefore, the system is amended depending on the type of gemstone being graded. A TYPE I gemstone grows flawless or nearly so and would be graded strictly like a diamond. A TYPE II gemstone grows somewhat included and inclusions are more common. Grading is more lenient. A TYPE III gemstone is almost always included and grading is most lenient.

Cut for colored stones will examine the proportions and finish looking at factors suck as outline balance, depth, bulge, windowing, extinction, polish and symmetry.

When the above factors are analyzed, the final grading will be assessed according to the standards as set forth in The Guide. Grading used will be Commercial (Lower, Middle or Upper), Good, Fine or Extra Fine.

COLORED STONE TREATMENTS

Colored stones are often subjected to various treatments to improve their appearance. Treatments are considered usual and customary practices when properly disclosed and when done without intent to defraud the consumer. Many treatments are stable and do not require special care. Others may require special care. When a treatment is detected and considered not to be usual and customary it will be so noted by this appraiser. Some treatments are reversible and re-treatable. It may be beyond the scope of an appraisal to determine the exact treatment methods or the amount of treatment present. Some treatments require sophisticated equipment to identify, not found in a standard gemological laboratory.

All treatments should be disclosed to the purchaser. Market values are generally based on these treatments. Unless otherwise stated, the colored stones in this appraisal are assumed to have been subjected to one or more of these treatments, when it is common for that species or variety, and valued accordingly. Treatments, when detected will be noted by the appraisal. Untreated gemstones, when detected and when the value is affected, will be noted. Unstable treatments or other treatments that adversely affect the value will also be noted in the appraisal when detected.

The following list describes some common gemstone treatments. It is not inclusive of all treatments.

Gemstone

Treatment

Frequency

Stability

Care of Gem

Ruby

Heat, possible residue

Usually

Excellent

Normal

Sapphire

Heat

Usually

Excellent

Normal

Emerald

Oil, Opticon or other polymer resins

Usually

Fair to good

Caution

Tanzanite

Heat

Always

Excellent

Caution

Pearl

Bleach

Usually

Very good

Caution

Opal

Oil, wax, epoxy

Rare

Fair

Caution

Blue Topaz

Irradiated

Always

Excellent

Normal

 

 

 

 

 

 

 

 

 

 

 

 



 

 

 

 

 

 

Other Gemstone treatments include irradiation, dye, various coatings, and diffusion. Some treatments such as dye may be considered fraudulent if not properly disclosed.

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