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Colored Stone Grading - Cut

The cut grade is a combination of three grades: brilliance, proportions, and finish. Once each grade is established, an Overall Cut Grade is assigned, according to these criteria.

Brilliance Grade:

We grade brilliance by visually evaluating of the overall light return and sparkle of the gemstone. Diamonds are graded based primarily on total light return, while color is king for colored stones. A good diamond will be brilliant over 90% of its face, while a very fine colored stone may show only 70% light return.

We use the standard GIA terms to describe the face up brilliance (light return) of a colored stone. These can be summarized with approximate numerical equivalents as follows:

We grade light return by observing the stone at approximately 20 inches from the eye, under a daylight equivalent light source, approximately 10 to 12 inches above the stone, with a white background. An estimated percentage of brilliance, windowing, and extinction are made, and then combined to place the stone in the above scale. Rarely do colored stones achieve an excellent brilliance grade.

Proportion Grade:

Because of their relative rarity, we give colored stones much more leeway when considering proportions than we do diamonds. And since the optic properties, cut design and critical angles vary for each gem type, no single formula exists for evaluating the proportions of colored gems. The system is divided into two sub-grades: face-up proportions and profile proportions.

Face-up proportion is based on evaluation of symmetry and appeal.

Symmetry is the equality between corresponding parts of the stone viewed face-up. Face-up symmetry flaws include:

Appeal grades the aesthetic look of the face-up shape of the colored stone. Appeal flaws include:

To grade the face-up appearance of a gemstone, we would note the specific factors and the degree to which they are present, with symmetry carrying the most weight. We then combine them and assign a single overall grade from excellent to poor.

Profile is based on an evaluation of profile symmetry, pavilion bulge, table size, and girdle thickness. Profile symmetry faults are:

Bulge is estimated by visualizing a straight line from girdle to keel (or culet), and then estimating the bulge that extends outside that line. Acceptable amounts of bulge are generally in the 5 to 15% range, depending on the cutting style and shape of stone.

Table size is an estimate that compares table width to the total width of the stone, expressed as a percentage. "Small" is less than 33%, "large" is greater than 67%, and "acceptable" is anywhere in between.

Girdle Thickness is a visual judgment made by holding the stone table to culet, then rotating it 360 degrees. Girdle thickness is disregarded at points or in the clefts of hearts, and is described as acceptable or unacceptable.

Symmetry generally counts the most towards the overal profile grade, but beauty, durability, suitability for setting, and extra weight are evaluated as well. The grade is given in the following terms:

Finish Grade

We care about craftsmanship. Our finish grade is based on the GIA system, scoring the polish, facet symmetry, and surveying the total count and size of facets (facet survey).

Polishing blemishes are noted as follows:

Facet symmetry flaws are noted as follows:

For polish and symmetry, we note the specific factor and the degree to which it is present, minute, minor, moderate, noticeable, obvious, or prominent.

Facet survey considers the size and number of facets in relation to the stone’s design and size, and will be described as too few, acceptable, or too many.

The overall finish grade combines the three factors, with polish and symmetry carrying the most weight, and expresses the combined effect in the following terms.

Overall Cut Grade

Once the three cutting components, brilliance, proportions, and finish have been assigned a grade ranging from excellent to poor, we then combine the three factors into an overall cut grade ranging from 10 to 1. The GIA and GemGuide terminology are related as follows, as seen in the Gem Guide Use section, p 9, F/W 2008-2009.

GIA Excellent – Gem Guide 8—10 Extra Fine

GIA Very Good – Gem Guide 6—8 Fine GIA Good – Gem Guide 4—6 Good GIA Fair – Gem Guide 2—3 Middle to upper commercial GIA Poor – Gem Guide 1—2 Lower to middle commercial