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Fish Eye Effect? Impact on light performance? What causes it?

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venus

Rough_Rock
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Mar 8, 2009
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Can someone please explain how the presence of a "fish eye" affects a round brilliant''s sparkle and brilliance? Does it mean the stone is poorly cut? Does a "fish eye" mean a stone will not be sparkly and brilliant? Thanks in advance.
 

Todd Gray

Brilliant_Rock
Trade
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Jan 20, 2009
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Date: 3/17/2009 4:00:56 AM
Author:venus
Can someone please explain how the presence of a ''fish eye'' affects a round brilliant''s sparkle and brilliance?
What sparkle and brilliance? It''s called a "fish eye" because it''s dead
 

venus

Rough_Rock
Joined
Mar 8, 2009
Messages
17
Yes, well, it's common knowlege that it's undesirable and affects the value or desirebaility of a stone. I was actualy hoping for more technical or indepth information about what causes it from someone knowlegeble about cuts.....No, I do't own such a stone but I'd like to inform myself about this....and as much about diamond cuts as possible....
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
What is interesting is here is the girdle reflection image for the default DC tolk which is considered the standard for comparison.
What a fish eye is when the girdle reflection decreases the brightness of the diamond and forms an obvious eye.
It is actually pretty hard to design a fisheye.

tolkgirdlereflection.jpg
 

Rockdiamond

Ideal_Rock
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Jan 7, 2009
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8,071
Date: 3/17/2009 3:19:08 PM
Author: venus
Yes, well, it''s common knowlege that it''s undesirable and affects the value or desirebaility of a stone. I was actualy hoping for more technical or indepth information about what causes it from someone knowlegeble about cuts.....No, I do''t own such a stone but I''d like to inform myself about this....and as much about diamond cuts as possible....
HI Venus,
Let''s simplify it- not that anyone is not capable of grasping the concept- but there can be other causes:
Generally a "Fish Eye" occurs when a diamond is cut too shallow.
What happens is that the girdle reflects into the table, forming a ring.
The effect is reminiscent of a fishes eye.

As Paul mentioned, such a stone would be quite difficult to sell.
Such a stone would not need to be judged by an expert, any sighted person would easily see the problem..
My feeling is that a true distinct "Fish Eye" is what can be called an "off make". This is a distinct difference form the subtle differences often discussed here. For example: variations within the GIA EX Cut grade. The "worst" of such stones is not going to be considered "off make"
 
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