Fish-Eye Effect

This is an image of a fish-eye. A fish-eye is a reflection just inside the table of girdle (on the opposite side). If the girdle is not polished and is thick the effect looks like a BIG circular inclusion, and can be as bad as an I3 (P3).

Fish-eyes are more apparent if the pavilion is shallow 39.5°, the table is large; the girdle is thick and not polished. Combinations of these factors worsen the effect.

Holloway Cut Adviser takes fish-eye into account. Fish-eyes occur proportionately between the following pavilion depths and table sizes:

41 degree pavilion  and  72.2% table
39 degree pavilion  and  58.4% table

These fish-eyes require no tilt to see them. If the table gets 1% bigger you see a 1% fish-eye. We rate fish-eyes with a negative value that reflects the effect a bit like an inclusion, because that is what it looks like. No tilt required is the worst fisheye, and Holloway Cut Adviser will give "do not buy this diamond under any circumstances as it is a fish-eye" comment.

A small amount of tilt to see a fish-eye is acceptable because these diamonds have a very good spread and look very big for the money. We measure and comment on how close a diamond is to a fish-eye by the distance under the crown facets to where the fish-eye would be on a scale of 0% - 5%. If the fish-eye was 5% or larger than the table size then we consider the diamond to be ideal.