Faceting, traditionally, is the cutting and polishing of flat planar surfaces in a geometric pattern on a transparent gem material. The “facets” are cut utilizing diamond charged, flat disks that revolve horizontally on a machine much like a record on a phonograph (See illustration A). These facets are shaped by how many facets and at what angles one places them to intersect with one another, but, they all two dimensional….they have length and width (see illustration B).
Illustration A Illustration B
Concave facets, uniquely, are three dimensional. They have length and width defined in exactly the same way as flat facets, but, they also have depth to their shape because the cutting and polishing is accomplished through the use of diamond charged round cylinders mounted horizontally on a machine (See illustration C). Cutting in this manner creates concave conical facets that are three dimensional in shape (See illustration D). Depending on the diameter of the cylinders being used, the gem cutter can control the depth and sharpness of the curved, three dimensional facets. Indeed, many of the best concave gem designs employ a number of different radii of curvature. Knowing when, how, and what size to employ them is the real art!
Illustration C Illustration D
The cutting and polishing of three dimensional facets is exponentially more difficult and labor intensive than simple, two dimensional flat faceting. There is a far greater demand for hand to eye coordination and sensitivity…not to mention the depth of understanding for the optics involved (See illustration E).
Illustration E
Why are concave faceted gems superior? In a nutshell, it is because three dimensional facets have a mathematically greater opportunity to reflect and return more of the ambient light and return it to the observer in the form of brilliance.
Of course, it is not all that simple, but it is interesting to note that an improperly cut, flat faceted gemstone may only look good at one observation point in really good light. Even a well cut flat faceted gem has a tendency to only look really good either at a few vantage points in really good light or from a single vantage point in subdued light.
But the strength, beauty, and value of a well cut concave faceted gem is such that it looks great at a large number of vantage points both in good lighting and in subdued lighting!
One is amazed at the beauty and brilliance of a well cut concave faceted gem in candle-light, at dusk, or in any diffused lighting condition. Indeed, it is the test of any gem to observe how it looks in poor light. And concave faceted gems continue to captivate and attract. This is its greatest appeal…beauty at all times, everywhere, in all kinds of light!
I. General Optical Affects
A. Diffusing aspects of pavilion facets 1. Promotes homogeneity in brilliance 2. No hot spots or dead spots in fancy shapes 3. Diminished color zoning 4. Softens the brilliance...no harsh planar reflections which often overpower the sublety of light body colors (such as aqua)
B. Dramatic increase in brilliance 1. Has appearance of having many more facets than are really there 2. Makes the gem seem to have a higher R.I. than it really does (Quartz looks like Beryl, Beryl like Topaz, Topaz like Corundum, and Corundum like Diamond!)
C. Darkens tone of gem material by 1/4 tonal grade
D. Conical crown facets focus and magnify light into pavilion
II. Other Advantages of Conical Facets
A. Best cutting technique for light to medium dark toned gem material B. Can use shallower pavilion angles and still produce a very brilliant gem C. Can create aesthetic, new gem shapes with interior curved outlines D. Improves brilliance in all but the darkest gem materials E. Dramatically reduces “extinction” which is so prominent in “fancy” flat faceted shapes such as pear, marquise, oval, etc
III. Other Considerations
A. Cylinders of different diameters can be used to create different curvatures of facets within a single gem design B. Multiple curvatures in combination with flat facets yields unparalleled designs and brilliance C. Potential for unique designs are virtually limitless considering the vast number of variables that can be employed on the pavilion, crown, and girdle outlines
