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Question re: Cut

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ImpatientOne

Brilliant_Rock
Joined
Oct 19, 2006
Messages
1,394
My question has to do with cut. If a diamond is graded as Very Good or greater, can it still be a poor preformer? My friend and I were comparing diamonds - her appraisal by a GIA graduate lists the diamond as Very Good (GIA cert is older so doesn''t list cut) . Anyway, I had her plug the numbers into the HCA on this site and it came back as fair for fire and scintilation...BTW, her stone is very eye pleasing (although I like mine better
)

I assumed (perhaps incorrectly) that the very good cuts and better would naturally be better perfromers... So what''s the deal?
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
ImpatientOne, I think the general answer is yes - it is possible to find a GIA graded VG cut which is still a great performer and vice versa.

See Garry's article: GIA Excellent Cut Grade: Case Study . This page in particular shows three diamonds one of which (A) has VG GIA grade.

Also see how Maarten de Witte from Hearts on Fire preferred GIA VG Looking at ideal Tolkowsky and slightly shallow cut stones. We witnessed quite a few other cases when people preferred certain GIA VG to EX in different lighting conditions.

Could you post proportions for that diamond here? Did you see the stone and were able to compare it to others?
 

DBM

Shiny_Rock
Joined
Oct 24, 2006
Messages
404
i think there''s also a little bit of disagreement in the fundamentals of what is considered "eye-pleasing". GIA can give a stone a high cut grade even if there''s considerable spots of black/dark areas provided that the dark provides a nice white/black contrast with the bright parts. Others i think go by "the maximum" outputs as being the gauge. the more light reflected on the physics level the more its a better cut. .. i''m sure there''s a ton of this topic discussed on the forum here, i haven''t seen it, just mentioning my understanding from my own studies.
 

belle

Super_Ideal_Rock
Joined
Nov 19, 2004
Messages
10,285
generally speaking, yes, it is absolutely possible. that's why it is important to know the angles and proportions on the diamond and why it got the 'very good' grade. don't get lulled into thinking that getting an 'excellent' assures you a top performer. i have a perfectly perfect gia 'very good' that got dinged for the 'thin' girdle. performance wise, it tops them all but because of the girdle, gia said it was only 'very good'

just know what you are getting.
 

ImpatientOne

Brilliant_Rock
Joined
Oct 19, 2006
Messages
1,394
GIA graduate from the PS Appraisers list graded the diamond as Very Good cut. GIA cert is older without pavillion or crown info, but per my friend the appraisal says the following:

Total depth 62.2%
Table % 59%
Pavillion Depth 45%
Crown Angle 34.0 degrees

If you plug these into the HCA, is says fair to poor...

How can a diamond be graded as Very Good cut with these numbers? It''s a beautiful looking stone from what I have seen. Is the HCA not always valid or just a guideline? Are other things taken into consideration?
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
How accurate are crown and pavilion measurements. Crown and pavilion numbers look rounded. How they were measured? (Sarin or Ogi machines?)

Any system GIA, AGS, HCA, etc. require accurate measurements.

45% pavilion depth is a bit too deep?

You can also plug these numbers into gia''s facetware
 
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