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Judging Sapphire Quality


What Is ‘Cut’ In A Stone?

The term “cut” can have several meanings when applied to sapphires and other gemstones.  For example, it may describe the faceting style or shape of a finished gemstone. The term also refers to a gemstone’s proportion and finish.

Proportion refers to the rough dimensions and overall symmetry of a gemstone.  Finish describes the precision with which facets meet, the relative size and number of facets, and the quality of the stone’s polish.

Like most transparent gems, sapphires reveal their full beauty when they are cut.  However, because sapphire rough is so valuable, dealers and consumers accept gemstones without the precision cuts required of fine diamonds.  In general, gem cutters follow four guiding principles when they fashion sapphires:

  1. Maximize the apparent color of the gem. A skilled gem cutter can influence the apparent color of the stone by maximizing a stone’s brilliance or amount of light returned to the viewer’s eye.
  2. Maximize the gemstone’s final weight.  This may be constrained by the sapphire’s crystal habit or growth-form.
  3. Minimize the appearance of undesirable inclusions or color zoning.
  4. Filling consumer demand for certain fashions or cutting styles.

Below Are A Few Terms Relating To Cut:

Face-up cut grade diagram
Face-up cut grade diagram

Symmetry Grade: an assessment of a gemstone’s proportion, balance, and uniformity determined by a number of criteria including length-to-width ratio, bilateral mirror images, etc.

Face-Up Cut Grade: an evaluation of a gemstone’s symmetry, proportion, and appeal while viewing the stone with its table facing the viewer.

Profile Cut Grade: an evaluation of a gemstone’s symmetry, proportion, bulge, table size, and girdle thickness while viewing the stone from the side.

Profile cut grade diagram
Profile cut grade diagram

Table Size: is calculated as a percentage of the gemstone’s total width. The table is described as small if its size is under 33%; acceptable if it is 33-67%; and large if it is above 67%.

Table size diagram
Table size diagram

Girdle Thickness: the average thickness of the gemstone’s girdle, which is the junction between the crown and pavilion of the stone.

sapphire girdle thickness diagram
sapphire girdle thickness diagram

Overall Cut Grade: Overall Cut Grade: an assessment of a gemstone’s cut based on its symmetry, windowing, extinction, brilliance, face-up cut grade, and profile cut grade.

Sapphire overall cut grade diagram
Sapphire overall cut grade diagram

Window: an area in a transparent gemstone where the body color appears to be see-through or watery. This occurs when the crown or pavilion angles are cut shallowly, causing light to leak out of the pavilion.

Brilliance: the amount of light that a cut gemstone reflects back to the viewer from the interior of the stone. Brilliance is a consequence of cut and it is an important characteristic because it determines the perceived liveliness and color of a gemstone.

Extinction: an area of a transparent gemstone where the body color looks very dark to black. This occurs when gemstones are cut with excessively deep pavilions.

After cut, the final determining factor of worth with sapphires is Carat weight.

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