The Bow Tie Effect in Diamonds
Diamonds are carefully graded according to their shape, size and brilliance. The refraction of light through the facets, or small faces, of the diamond contributes to its brilliance, and the more precise the stone's cutting, the more brilliant the diamond will be. Refraction and geometry also contribute to light effects such as the bow tie, which is common in certain shapes and should never be too prominent to the unaided eye. Does this Spark an idea?
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Causes
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The bow tie effect arises from the geometry of the tiny facets (faces) that are cut into the pavilion, or lower section, of the diamond. In certain cuts, the ends of the pavilion are narrower than the center. If incorrectly or inaccurately cut, these pavilion facets will strongly affect the reflection of light in the upper crown portion. From above, two long and narrow dark areas can be seen on opposite sides of the stone, and joined at the middle, resembling the shape of a bow tie. They remain dark even as the viewing angle changes.
Types
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The less round and longer the stone, the more likely it is to show the bow tie effect. Certain cuts of diamonds, especially oval, marquise, pear-shaped, and radiant, are more likely to show the bow tie effect. If the bow tie appears very large, or can be seen easily without the use of a magnifier, it affects the stone's brightness and appearance and brings down its value. Deep pavilions are more likely to display dark areas. Shallow pavilions, however, generally have less brilliance.
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Prevention/Solution
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There is no accepted grading or measurement standard for the bow tie effect. Generally, the higher the crown, the less likely the stone is to display a bow tie. There is no way to determine in advance if an uncut stone will show the effect. Eliminating the bow tie depends to some extent on the skill of the diamond cutter.
Angles
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The bow tie usually appears horizontally across the center of the stone, when viewed from above. It can be very faint, or so prominent that it blacks out an entire large section of the stone. It can appear in clear diamonds as well as colored stones such as emeralds and rubies, and cannot be eliminated through the use of settings.
Considerations
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If you are shopping for diamonds, have a close look at the stones through a jeweler's loupe, or magnifying device. Don't accept a stone with a prominent bow tie, or the explanation that the bow tie effect is inevitable or desirable. If you want to avoid a bow tie altogether, remember that a certain amount of bow tie is common in marquise and other elongated cuts, but is never present in brilliant or round cuts, which are symmetrical.
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References
- Photo Credit single diamond ring image by OMKAR A.V from Fotolia.com
