A fish-eye is a dull ring that shows under the table of a round diamond. It is a reflection of the girdle, seen when the pavilion is too shallow.
In more detail
A large table makes it worse, and it shows more as the stone tilts. GIA counts a fish-eye against the pattern in its cut grade. IGI's round cut chart caps the grade at Fair when a fish-eye is present.
On a grading report
Not a line of its own. On an IGI round, a fish-eye limits the cut grade to Fair.
Related terms
- Pavilion angle: The pavilion angle is the slope of the pavilion mains, measured against the plane of the girdle.
- Table size: Table size is the width of the table as a percentage of the average diameter.
- Cut grade: The cut grade rates how well a diamond's proportions and finish work, from Excellent to Poor. GIA gives it only to standard round brilliants in the D-to-Z color range.
- Windowing: A window is a face-up area through which you can see straight through a stone. It forms where pavilion facets are too shallow to reflect light, so light passes out of the back.