Summary: Bowtie Effect in Diamonds
The bowtie effect shows up in some fancy shaped diamonds as a shadow that looks like a bowtie.
The Bowtie Effect refers to a shadow that can be seen in some Fancy shaped diamonds, such as Marquise, Pear and Oval (there is a similar effect found in the Heart shape, but it is not actually a bowtie). As the name implies, the shadow looks like a bowtie, seen across the middle of the diamond, or east to west when looking down on the diamond's table. This can have a negative impact on the overall beauty of the diamond, but it is not necessarily so.
It is generally believed that the bowtie effect is caused by a leakage of light in part of the diamond. This is only somewhat accurate. What actually causes the bowtie effect is the shielding of light by the human head. By simply looking at the diamond, you will be blocking some of the light that can enter into it and be returned to your eyes.
The blocking of light is but one reason for the bowtie effect. Another reason explains why some diamonds have a darker bowtie than others. This is where the facet, pavilion and table angles come in to play. When these are all angled and proportioned correctly, the bowtie effect will be minimized, as the light is reflected and refracted within the diamond so as to diffuse the area that is in shadow.
It is a common misconception to think that by simply elongating or shortening the pavilion that the bowtie effect can be diminished. However, it is important to remember that the bowtie effect is not determined by the pavilion angle alone. The degree of the crown angle must be complementary to the degree of the pavilion angle in order to properly and effectively minimize the bowtie effect.
The bowtie effect does not need to be seen as a major flaw. For one thing, from a short distance the bowtie effect cannot be seen. A minimal bowtie effect will not have an impact on the overall brilliance and clarity of the diamond. Therefore, if you cannot see the bowtie effect from a reasonable viewing distance, it is not affecting the diamond.
In addition to this, the bowtie effect can often add a pleasant and aesthetically pleasing contrast in diamonds. By having a sharply defined bowtie, especially if it is light in color, the brilliance of the diamond will only seem brighter and sharper. Essentially, it is up to your own eyes and opinion as to whether or not the bowtie effect has a negative impact on a given Fancy shaped diamond.