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Is this a fisheye?

Amccaffery89

Rough_Rock
Joined
Jan 15, 2016
Messages
2
Round brilliant
Carat 1.00
Color I
Clarity SI1
Polish good
Symmetry very good
Fluorescence none
Cut good



Measurements 6.22x6.26x3.96
Girdle thick to very thick
Star length 55%
Table 58%
Total depth 63.4
Crown height 15%
Pavilion depth 42%
Crown angle 36
Pavilion angle 40.2
Lower girdle 80%
Cutlet very small
 

bluelotus

Shiny_Rock
Joined
Feb 20, 2013
Messages
257
I don't think so. When you run the numbers in the Holloway Cut Advisor it comes up as a 1.2 - Excellent, FIC (firey ideal cut). I wonder if this might be an antique/vintage stone.
 

John Pollard

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,559
The fisheye-effect occurs when a diamond's pavilion is shallow and the table is large. In certain proportions-combinations the girdle outline can be seen reflecting within the table.

This diamond has a shallow pavilion and a girdle running to very-thick. While not overt, it is likely that you'll be able to see the girdle outline reflecting under a portion of the table's circumference after a certain degree of tilt. Not a full-fisheye, but hints of that effect. More importantly: While the shallow pavilion angle average is somewhat offset by the crown angle, these proportions are obstruction-sensitive, meaning that it will get darker as the viewer gets closer to it. For the reasons above, these proportions are predicted as candidates for AGS 6-7 in light performance.

I'd also note that, at 6.24 mm average diameter, it's a 1.00 carat diamond that only has the physical spread of diamonds near 0.90ct.

bluelotus said:
I wonder if this might be an antique/vintage stone.
Right. At first blush (girdle, culet, crown) I thought so too. But the lower-half lengths and table size seem out of character for antique fashioning. Possibly an old cut that was damaged and later "improved" (ymmv).
 

bluelotus

Shiny_Rock
Joined
Feb 20, 2013
Messages
257
John,
I am a bit confused. I know that the Holloway Cut Advisor is meant to be used as an elimination tool and not a selection tool but I am curious to know why the pavilion and crown angle combinations defined as ideal in the HCA(BIC, TIC, FIC), would not correspond with AGS Ideal light performance. This diamond, while on the deep side due to a thicker girdle, still has a complimentary angle combination according to the HCA. How is it that it might score an AGS 6-7 for light performance? Is it simply that Garry Holloway's range for ideal is much broader?
All the best for the New Year!
 

Karl_K

Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
9,466
bluelotus|1453127165|3977483 said:
John,
I am a bit confused. I know that the Holloway Cut Advisor is meant to be used as an elimination tool and not a selection tool but I am curious to know why the pavilion and crown angle combinations defined as ideal in the HCA(BIC, TIC, FIC), would not correspond with AGS Ideal light performance. This diamond, while on the deep side due to a thicker girdle, still has a complimentary angle combination according to the HCA. How is it that it might score an AGS 6-7 for light performance? Is it simply that Garry Holloway's range for ideal is much broader?
All the best for the New Year!
Put it in a pendant or earring and the hca is right put it in a ring and ags is right about the basic angle combination.
This is due to the level of obstruction in the different viewing positions as alluded to by Sir John above.
The hca assumed a med girdle.
For the reasons stated by sir John above I would be hesitant even for an earring with that thick a girdle and that combination
 

John Pollard

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,559
Karl is speedy this morning. I was just typing a reply when his appeared.

Karl_K|1453133971|3977511 said:
Put it in a pendant or earring and the hca is right put it in a ring and ags is right about the basic angle combination. This is due to the level of obstruction in the different viewing positions as alluded to by Sir John above.
The hca assumed a med girdle. For the reasons stated by sir John above I would be hesitant even for an earring with that thick a girdle and that combination
Exactly.

Bluelotus, I would also ask: When you used the HCA what number did you use for culet? With those proportions, when you provide the minimum entry of 0.35% for the V Small culet the HCA should issue a warning that the girdle is overly-thick. That warning is independent from (and more significant than) the visual output prediction.
 
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