Concave Cut Gems

At one time, all gemstones were shaped as cabochons or carved, or simply polished in their natural form. The art of faceting gemstones really began in the 15th century in Europe with the invention of the horizontal cutting wheel. It then became possible to reproduce complex geometric faceting designs to control the light reflected from within a gemstone. Faceted gems have superior brilliance and fire because they maximize the light that is returned to the eye. 

Citrine Portuguese Cut 25.38 cts Citrine Concave Cut 50.64 cts Citrine Checkerboard Cut 19.88 cts
 Portuguese
Cut
 Concave
Cut
 Checkboard
Cut

Faceting design and technology has continued to develop. The most famous cutting style is known as the round brilliant cut, with 58 total facets (33 on the crown, 25 on the pavilion). Other well known faceting styles include the step cut, the portuguese cut, the checkboard cut, the barion cut, and the asscher cut.

Though these different styles vary according to the shape and number of facets, they all have one thing in common -- the facets are flat or 2 dimensional.

Concave cutting, a recent innovation, is a departure from the long tradition of faceting design. In concave cutting, the facets are three dimensional rather than flat -- they have depth as well as length and width. Where traditional two dimensional facets are created on a flat cutting wheel, concave cutting uses grinding elements in the form of round cylinders mounted horizontally on the cutting machine. Faceting in this manner creates concave conical facets that are truly three dimensional in shape.

Concave facets have different optical properties than two dimensional facets. In general, a concave facet refracts more of the ambient light and returns it to the eye as brilliance.  Concave cutting will thus increase the brilliance of a gem, while at the same time providing a diffusing effect, so that the brilliance is quite even, with no hot spots or dark regions, and diminished color zoning.

Usually only the facets in the pavilion (lower half) of the gem are cut with concave facets, with flat facets cut on the crown. This design can create interesting reflective patterns when one views the gem down through the table.

There are, however, some limitations with this cutting style. Larger gems cut with concave facets tend to show more brilliance than smaller stones. The effect is also more pronounced with lighter colored gems, and in fact concave cutting has the effect of noticeably darkening the tone of any gem. So concave cutting can in fact reduce the brilliance of darker colored gemstones.

Because concave cutting removes more gem material to cut the curved facets, economics become a consideration when dealing with more expensive materials. Though the difference is only perhaps 10% when compared to traditional faceting, you'll find that valuable materials like sapphire, ruby, spinel and tsavorite garnet are rarely, if ever, cut with concave facets. The fact that that high quality specimens of these gems tend to occur in smaller sizes with deeper, more saturated, color is also a factor, since they generally won't be improved by concave cutting. You'll tend to find concave cutting used for less expensive materials in lighter colors and larger sizes, particularly citrine, topaz and fluorite. 

See all our Fine Citrine, including many Concave Cuts

 
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