It’s a common fact a beautiful diamond should have every ray of light entering through the table facet back through it. But not all the stones are perfectly cut also known as poor make. For fancy cut stone such as oval, the imperfect cut is in the form of a “bow-tie” which appears as its name implies.
A diamond with bow-tie is a darkened area that runs across the width of the body of the diamond which literally resembles a man’s bowtie. The degree of the bow-tie carries a significant relation with the “cut” of a diamond. This manifests when diamond’s facets fail to reflect light properly regardless of any direction you turn the diamond making the stone dull. It is important to know, however, that bow-tie is not caused by leakage of light but mainly created by the obstruction of light when viewing the stone. When a person looks at the stone, the light rays that travel through the stone get shielded by the person’s head. And this obstruction brings dark looking shadows that get reflected within the diamond.