Colored Stone Appraisal | Charlotte Jewelry Appraisal
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colored stones

Colored Stone Appraisal?

 

Appraisals for colored stones (semi-precious or precious) are similar to that of the diamond appraisal in that the 4 C's; color, clarity, cut and carate weight are evaluated but unlike the diamond appraisal, the color of the stone is the determining factor of the gemstone's value.

 

The GIA (Gemological Institute of America) report provides detailed information about the dimensions, carat weight, shape and cut of a stone.

GIA reports also cover any treatments or enhancements that have been done and of corse, wether the stone is natural or synthetic.

A GIA report utilizes a "colored stone grading system" chart to graph the hue, tone, and saturation of a stone.

 

 

 

 

 Colored Gemstone Grading Basics

COLOR

Gemstone color grading is broken into three quantifiable categories: intensity (saturation), hue (color), and tone (lightness/darkness). The GIA specifies and labels up to thirty one gemstone hues. The "hue" is the actual "color" of the material (blue, geen, red, etc.).


Gemstone Hue Chart


Gemstone Color Grading System - Hue

The GIA nomenclature also specifies six levels of saturation ranging from "grayish" (neutral grey) to "moderately strong" to "vivid." The term "intensity" is also used to describe a stone's saturation.

Gemstone Saturation Chart


Gemstone Color Grading System - Saturation

To describe the darkness or lightness of a colored stone, the GIA system has nine levels of tone ranging from "very very light" to "very very dark." A numerical value is assigned to each label for use in a grading report.

Gemstone Tone Chart


Gemstone Color Grading System - Tone

With the exception of hue, each of these parameters by themselves are relatively meaningless and they must be used in conjunction to tell the full story of a gem's color quality. Taken together, these three parameters will provide a simple numeric code that can quickly and accurately quantify gemstone color.

Gemstone Grading Sapphire Chart


Sapphire Color Grading

Using a Kashmir or Cornflower blue sapphire as an example, in order to receive a 10 quality rating, the stone would posses a "violetish/blue" hue, with a 6 or "medium dark" tone and 6 or "vivid" saturation.

CLARITY

 Transparent colored stones are divided into three type classifications depending on crystal growth characteristics, and then graded within their type class, for clarity.

The G.I.A. grading system for colored stones lists clarity type classifications as Type I, Type II, and Type III. The classifications are defined as follows:

Type I

These are gems that grow extremely clean in nature and usually have no eye-visible inclusions. An example is Aquamarine.

Type II

These are gems that typically grow with some minor inclusions in nature and the inclusions may be eye-visible. An example is ruby.

Type III

These are gems that typically grow with many inclusions in nature and the inclusions are usually eye-visible. An example is emerald.

CUT

Colored stones are also graded for cut. Cut grading includes observance and qualification of brilliance, proportions, bulge, overall symmetry, and finish.

CARAT WEIGHT

The weight of diamonds and colored stones is expressed in carats. One carat consists of 100 "points" and is equal to 0.200 grams.

 

... Elisa J. Propst, GG

M. Gibbs, Ltd - Concord, NC

 

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