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Is it all about Cut?


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Hi all,

I just wanted to ask a question about Cut in relation to Round diamonds. I've been looking for an enagement ring and came across a nice 0.71ct / E / Ex / Ex / VS2 / girdle thin-medium / Fl none / GIA cert diamond.

Its has an older 2003 GIA cert & doesn't have the extra Cut info I believe the new GIA certs have. Is there a way to determine the Cut quality of the diamond from say the symmetry = EX & polish = EX info or are these 2 measurements not related to the diamond's Cut?

Or should I be looking for a diamond with a newer GIA cert? Btw the jeweller says its an EX cut.

A great site for newbies like myself. Thx (from Australia)

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People (vendors) have different ideas of what constitutes an "Excellent" cut. Some throw the term onto anything with excellent polish and symmetry. The proportions are ulitmately going to have the biggest impact on the brilliance and "sparkle" of your diamond.


Have you asked them for a Sarin report or something equivalent that shows you all of the diamond's proportions? Or if they have any light performance information on it?


Have you seen the diamond yourself and compared it to others of lesser or better cut quality?

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It’s not the lab report that makes a beautiful stone beautiful. Cutters were producing excellent stones way before 2006 so lack of a modern report is not a mark against it. When the jeweler says it’s an excellent cut, ask what he means by that.


The new GIA cut grading scale is based on 15 attributes:





Total depth %

Table %

Crown angle

Pavilion angle

Crown height

Star facet length

Girdle thickness & brillianteering

Girdle thickness %

Culet size




There is not enough information on a pre-2006 GIA report to estimate a GIA cut grade without examining the stone but your jeweler, assuming he has the tools, the training, the temperament, the time and the stone, should be able to do it.

You've already got 5 of them, and a Sarin report like Megan asked for will supply 4 or 5 more (depending on which model and report). The rest are done by trained observation.



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Neil and 10x bring up some great points

10x mentioned the way some sellers try to substitute the "Polish" and "Symmetry" grades for a cut grade.


I have a stong view that people promoting this idea, are doing a disservice to consumers.

I've seen drop deap gorgeous stones with "Good" polish and symmetry, as defined by GIA.

I've also seen butt ugly diamonds graded VG or EX on polish and or symmetry.

SO- consumers limiting thier search to VG or better might miss the best diamond.


As Neil pointed out, there were "Killer Makes" long before GIA even considered a "Cut Grade" for round diamonds. YOur jeweler should show you the diamond along with others - and show you how great a well cut diamond looks.


If it's an online seller, have they provided photos?

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Thanks 10x & Neil for your fast replies.


The diamond has no other reports with it only the older style GIA cert. I think 10x is right in that the jeweller is probably assuming that EX symmetry & polish equates to EX cut. After learning from this forum how important cut is I wanted to be sure.


This store is relatively small so I doubt the jeweller can carry out the analysis that Neil has suggested. I have sighted the diamond (using a 10x loop as well) & it looks fine to me (newbie eyes considering). I wanted to be sure that the cut was in fact EX or ideal.


Hmmm I'm not sure what to do about this particular diamond now. However I realise why it is so important to get a GIA, HRD, AGL cert when purchasing a diamond.


Should I copy down the dimensions of the diamond(s) next time? From these measurements is it another method to determine the cut quality?

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Hi David,


No pics since its not an online store but a small jewellery store.


I've sighted it against two other diamonds both with pre 2006 GIA certs unfortunately so I dont know what the cut of these 2 are either.

0.61ct / E / VS2 / VG / VG (modified cut)

0.71ct / F / VS2 / VG / G

I think I've rememeber the specs correctly for the above 2 diamonds.


Against the above 2 the diamond I'm interested in it looks very slightly brighter & how should I put it in newbie terms "clearer/cleaner" when you look straight into the table with or without the loop.


I wish it had a 2006 GIA cert with it B)

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As an online seller of diamonds, I believe it's very important to convey to the consumer visual reports and images of how the diamond looks.


Photos are important and measurement of light performance are important.


The Brilliancescope (www.gemex.com) measures a diamonds light performance and is a valuable tool.


You have the advantage of seeing these diamonds.


Trust your eyes.

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