Diamond expert advice - GIA and DCLA discrepancy

[nuffsaid]

Hi

I figured I might as well start a new post so that others can specifically see the info regarding the subject above.

I am close to finalising the purchase of a stone with a GIA report and have also subsequently got it graded by DCLA to be sure everything was spot on. I am looking for a close-to-ideal-as-possible cut and found a GIA with one. However DCLA numbers are slightly different as below:

(GIA on left, DCLA on right)

Depth_______61.7___61.2
Table_______57_____58.2 (note GIA does not do decimal places)
Crown_______34.5___34.8
Pavil_______40.8___40.8
Culet_______None___0.5
Girdle______4%_____3.9%
HCA_________1.4___ 1.7

GIA says cut, polish, symmetry are all EXC
DCLA says proportion grade, symmetry, polish, transparency all EXC
DCLA have commented on it being a beautiful stone

Same stone being graded as DCLA has noted the GIA inscription.

Could well be using different Sarin machines (BrilliantEye, DiaScan, DiaMension)
Just not sure if the table size difference is large enough to be concerned about

Thanks in advance for your help...the novice in me just keeps doubting haha

 

[strmrdr]

those are some large differences.
Someones scanner was goofy.

 

[nuffsaid]

Which difference should concern me?

And is this a regular occurrence, I wonder which is more accurate. For all I know, either could be wrong.

I understand that GIA have a habit of rounding things, sometimes in a more favourable direction?

 

[strmrdr]

.5% depth difference and the CA is outside the gia rounding zone.

 

[Paul-Antwerp]

Do not worry about the crown-angle-difference, it is most probably a minor measurement-difference that becomes bigger because of GIA-rounding.

More important is the depth-difference. That should be spot on. And it is easy to verify manually.

Live long,

 

[nuffsaid]

Wow thanks all!

- What is GIA's rounding like?
- Is the difference in table a concern?
- How can you verify depth % manually?

More data

(GIA on left, DCLA on right)
Diameter____7.49-7.51___7.51-7.53    
Depth_______4.63mm______4.6mm

 

[nuffsaid]

Looking at the above post, my calculations show that the depth % difference comes from the small difference in diameter and depth.

 

[denverappraiser]

Sarin’s stated calibration accuracy is +/- 0.2. You’re slightly outside of that with your table measurement but others are within that range (note: Depth percentage is calculated from several other figures, it''s not a direct measurement). I’d be willing to bet it’s a calibration issue on one or both machines at the time of the scan and not any sort of problem with the stone or any evidence of a mismatching. If you have to choose one as more reliable, bet on GIA.


Neil Beaty
GG(GIA) ICGA(AGS) NAJA
Professional Appraisals in Denver

 

[nuffsaid]

I might go talk to DCLA about it, any questions I should ask?

So I shouldnt be concerned then, both the reputable merchant and DCLA say it is a fantastic stone