What has a fish got to do with buying a diamond? Well, if your diamond’s appearance resembles that of a fisheye, there’s nothing to rejoice about. You have just made a bad mistake and purchased a terribly cut diamond.
In this write up, you are going to find out what a fisheye diamond is (with real-life examples) and how you can avoid buying such diamonds…
This diamond has a fish eye and a really dark ugly contrast patterning.
When diamonds are cut too shallow, the internal reflections of the girdle would be seen inside the table facet. This creates an image of a grey ring that is distracting and unpleasant to look at.
People in the industry refer to this phenomenon as a fish-eye because it does look very much like one. And trust me, a fish-eye diamond ain’t pretty at all.
It doesn’t matter if the diamond has the highest clarity (IF), best color (D) or other attributes on a grading report that may suggest a “beautiful” looking stone. These kinds of stones suffer from a lack of brilliance and look plain ugly.
In extreme cases, this cut defect can look as bad as an I3 type of inclusion.
A fish-eye is formed when the diamond’s girdle reflection is seen under the table facet.
Examples of badly cut diamonds with shallow depth and lousy proportions.
The examples above show diamonds with some degree of fisheye effects in them. The severity of this phenomenon is dependent upon a number of factors such as:
Here’s a quick explanation of why the above factors affect the fish eye. Due to the way light travels, lower pavilion angles would cause a diamond to have less brilliance and make cut defects even more pronounced.
As light enters the diamond, the shallow depth causes light rays to be reflected from the girdle back through the table. This is the reason why a thicker girdle and larger table will make the fish eye effect more severe.
Fundamentally speaking, the fish eye effect is a result of poor cut proportions. If you follow my proportion guidelines for a round diamond here, I guarantee you will never end up with such a diamond.
Yes. Technically speaking, the fisheye effect is caused by shallow pavilion angles and large tables. Shapes like ovals, pears and hearts would also exhibit this effect if they are cut with a bad combination of angles.
This heart shaped diamond shows symptoms of a fish eye forming under the table facet.
I’ve included a couple more examples below where you can click on the images to view problematic diamonds in 360° videos.
To conclude, the fish-eye effect is an indication of very poor cut and is very distracting to see in a diamond. Unlike subtle problems in clarity or nuances in color, you don’t need to be an expert to notice this issue. If you do see them, avoid them like the plague.