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Cut Metrics - EGL USA vs. GIA

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grayaug

Rough_Rock
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Is it safe to assume that the cert cut stats are accurate on GIA and EGLUSA certs? i.e. table, depth, crown and pavilion

Meaning, the data points that are entered into the HCA cut advisor are generally precise for both grading entities when compared against each other.as/

My research from this site indicates EGL USA grades color HIGHER than GIA in general. Sometimes one grade higher.

My research from this site indicates EGL USA grades clarity as/more strictly than GIA. Less common that the color grade spread.

Why do the selling sites include the polish and symmetry and not the cut. Isn''t the cut grade a far more important attribute?

Will the recession drop prices on these web sites?
 

Lorelei

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
42,064
Date: 3/29/2009 10:05:28 AM
Author:grayaug

Is it safe to assume that the cert cut stats are accurate on GIA and EGLUSA certs? i.e. table, depth, crown and pavilion

Meaning, the data points that are entered into the HCA cut advisor are generally precise for both grading entities when compared against each other.as/

My research from this site indicates EGL USA grades color HIGHER than GIA in general. Sometimes one grade higher.

My research from this site indicates EGL USA grades clarity as/more strictly than GIA. Less common that the color grade spread.

Why do the selling sites include the polish and symmetry and not the cut. Isn't the cut grade a far more important attribute?

Will the recession drop prices on these web sites?
GIA round the numbers so there is some variance, EGL use percentages which are not as accurate as angles, in order to get more accurate measurements a Helium or Sarin scan is needed. Using the numbers on the report will give you an idea when entered into the HCA if a diamond is worth further consideration or not, and to follow up with ASET or Idealscope images in order to learn more about the diamond.

Polish and symmetry is almost always mentioned for each diamond, until a few short years ago GIA didn't even grade for cut, vendors have often used labels such as Ideal Cut, Premium Cut etc but this is no guarantee of a well cut diamond.

EGL USA is said to be the strongest of the EGL labs but I don't think it is usual that they grade colour more strictly than GIA in general. Each diamond needs to be taken on a case by case basis, there was a study done here a few years ago concerning this but it was a while back now. If you have an EGL diamond in mind then get an independant appraiser to inspect it for you to make sure the colour and clarity check out, I have an EGL USA diamond which checked out to be the colour and clarity as stated.

http://grading.pricescope.com/method.aspx

Cut grades- unless one is referring to AGS0 Ideal cut then cut grades need careful evaluation to find the best performers ( and this can even be prudent with AGS0), yes cut is crucial but labels used either by vendors or GIA Excellent, Very Good and so on need careful checking to find which are truly the best cut out of these. Cut is THE most important factor in getting you a beautiful diamond.

Prices - hard to say what will happen really.
Also in conclusion the HCA is not used to select diamonds but to eliminate them, the HCA's job is to tell you which diamonds are worth further consideration, those which score <2. Once you get diamonds which do score below 2 then you need ASET or Idealscope images as the next step, particularly if buying online.
 

grayaug

Rough_Rock
Joined
Aug 12, 2008
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11
This data is from a Holloway, et. al. papers that performed a blind test where they sent out a series of stones to multiple grading agencies and posted the results.

It is available on this site.

In general GIA grades stricter on color than EGL USA. Meaning a GIA "I" could grade out as an "H" on a EGL USA cert a % of the time.

The EGL USA grading entity was in alignment with GIA and in a few instances was actually stricter on clarity grading.

My takeaway from the paper was that I would definitely consider an EGL USA graded stone and simply perform a color downgrade to get to a comparable GIA stone to compare apples to apples vis-a-vis pricing.

EGL USA = I, SI2
compare to
GIA = J, SI2
 

canuk-gal

Super_Ideal_Rock
Premium
Joined
Apr 19, 2004
Messages
21,027
Date: 3/29/2009 11:23:47 AM
Author: grayaug
This data is from a Holloway, et. al. papers that performed a blind test where they sent out a series of stones to multiple grading agencies and posted the results.

It is available on this site.

In general GIA grades stricter on color than EGL USA. Meaning a GIA ''I'' could grade out as an ''H'' on a EGL USA cert a % of the time.

The EGL USA grading entity was in alignment with GIA and in a few instances was actually stricter on clarity grading.

My takeaway from the paper was that I would definitely consider an EGL USA graded stone and simply perform a color downgrade to get to a comparable GIA stone to compare apples to apples vis-a-vis pricing.

EGL USA = I, SI2
compare to
GIA = J, SI2
HI:

Very small sample used in that study and therefore one is not able to generalize those findings to suggest with certaintly that GIA provides softer grading than EGL USA.

cheers--Sharon
 

Lorelei

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
42,064
Date: 3/29/2009 11:23:47 AM
Author: grayaug
This data is from a Holloway, et. al. papers that performed a blind test where they sent out a series of stones to multiple grading agencies and posted the results.

It is available on this site.

In general GIA grades stricter on color than EGL USA. Meaning a GIA 'I' could grade out as an 'H' on a EGL USA cert a % of the time.

The EGL USA grading entity was in alignment with GIA and in a few instances was actually stricter on clarity grading.

My takeaway from the paper was that I would definitely consider an EGL USA graded stone and simply perform a color downgrade to get to a comparable GIA stone to compare apples to apples vis-a-vis pricing.

EGL USA = I, SI2
compare to
GIA = J, SI2
Your best bet would to be if you want to stick to EGL USA, find a diamond you like then make the sale final on an independant appraiser inspecting the diamond to make sure the colour and clarity check out - and that the price is right. I don't think you can really guarantee anything here especially on the basis of that survey. Also if you ever wanted to sell or trade in an EGL graded diamond, this can be more difficult still than GIA or AGS graded diamonds.
 
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