Posted on December 10, 2014 by Mary Hood | 0 Comments
A fisheye is the sign of a poorly cut diamond. Even if a diamond has high clarity and color ratings, a fisheye can scrap the brilliance of the diamond and give it a dead center—which looks a bit like the pupil of an actual fish’s eye. A fisheye may also be mistaken for a circular inclusion. This lowers the value and beauty of the stone.
Both fisheye diamonds pictured above have dull centers.
The unfortunate fisheye phenomenon occurs when the diamond is cut with shallow pavilion angles, a large table facet, and/or a thick girdle. The fisheye is a reflection of the girdle appearing just inside the table. The table size is directly related to how easily the girdles reflection may be seen while flat or shallow pavilion angles limit light dispersal, thereby reducing the stone’s brilliance.
A fisheye may also occur in a fancy-cut diamond (ovals, hearts, and pears) if the stone is cut with a bad combination of angles.
Fisheyes may occur with fancy-cut stones as well.
To avoid a fisheye diamond, be sure to inspect the gem from all angles under various lighting. Check the pavilion angles on certified stones. A round-cut diamond's pavilion angles should typically be between 40.5 and 41.5 degrees.
Photos: Barbara Michelle Jacobs, Beyond 4Cs