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Reading GIA: understanding Cut on Round Diamonds


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I have been a short-time lurker and am finally making the plunge toward engagement - with some good advice.


But after reading a lot on this site, I cannot understand how to know if the Round Diamonds I have (with GIA certs) are Ideal, Excellent, Very Good, or Good Cuts?


As you know there are so many variables into what makes a dimaond an excellent diamond.


Here are the reports and I am simply not knowlegable about which is the better overall value:



Round Brilliant

Color: G

Clarity: VS2

Florscence: None

Measurement: 6.66 - 6.68 x 4.10

Weight: 1.12 c

Depth: 61.5

Table: 61%

Girlde: Medium to slightly thick faceted

Culet: None

Polish: Excellent

Symmetry: Very Good



Round Brilliant

Color: F

Clarity: SI1

Florscence: Medium Blue

Measurement: 6.93 - 6.99 x 4.22

Weight: 1.26 c

Depth: 60.6

Table: 58%

Girlde: Medium faceted

Culet: None

Polish: Good

Symmetry: Good


Both stones look marvelous to the naked eye and one is obviously larger than the other. That is what I can tell.


Other than that, what do you believe would be a fair price range for each stone?


Thank you to anyone who responds in advance

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GIA reports do not include information on cut (yet). This will have to come from an outside vendor. Most definitions of ‘ideal’ are based on the details of the facet angles as well as the polish and symmetry. Many dealers can supply you with this info if you ask them for it. A common report of this is called a Sarin report. If they can’t, or won’t get it, there are several appraisers that have the equipment and the skills to assist you with it.


Don’t get so distracted with the numbers and the lab reports that you forget to look at the stone. Beauty is in the eye of the beholder and not everyone agrees about what is best.


Neil Beaty


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Thank you for your quick response. I actually asked this question to the Diamond Broker with whom I was turned on to on the East Coast (I am on the West) and from where I received both diamonds for my review.


A friend of mine turned me on to this broker, so just to be clear I do trust my friends.


I asked the typical newbie questions: Color, Clarity, D this, F that, V this, VV that. He stated, matter of factly, "it is all about the cut."


I asked (using my Blue Nile reference that I read on their site): "is this an Ideal cut?"


He replied: "yes."


But I guess my main confusions are:


1 - If it is an Ideal Cut, do all the other line items on the report really matter?


2 - Is either of the Diamonds I wrote about above better than the other if they both look damn good - except one is inherently larger?


3 - what should a stndard price be for both individually?



Thank you again.

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Ask him what he means by 'Ideal'. Not everyone uses this word in the same fashion. The classic definition comes from AGS, which grades cut on a scale from 0-10 with 0 being the best. There is a brief discussion of this in the tutorial at the top of the page. If you use Google or some similar utility for a term like 'ideal cut diamonds' you will get thousands of dealers who will explain what THEY mean and what attributes they consider important. You'll quickly notice a pattern. Many of these will also feature price search utilities rather like the one at the top here called 'find an online jeweler'. Even if you don't end up buying from one of them, these utilities are useful for comparison shopping purposes. Many of them (although not the one here) will allow you to sort based on claims of idealness, Hearts and Arrows, and similar criteria. There are several highly competitive dealers who participate in this forum that have links to their sites at the bottom of their posts. Check 'em out.


Many dealers are now offering what they call 'super ideal' diamonds. These are stones where the dealers requirements are even more specific than the AGS specs. Most of these are also accompanied by an explaination about why their stones are better. Some can get a little long winded but there's a pretty good free education available if you're willing to wade through it with the usual warning that not everything you read on the internet is true. Good judgement goes a long way.


I won't give a value opinion on a diamond without seeing it because there are just too many variables. Both of the stones you list have good potential but neither one will meet the classic AGS-0 standards for ideal.


Neil Beaty


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It's impossible to tell what a diamond will *look* like by a few average numbers on a piece of paper. From the numbers, they are not in the ideal cut range. I've had stones sometimes that were not ideal cut do as good or better than an ideal cut in light performance. We use 2 different machines to communicate the cut of the diamond with our clients. To learn more about this information you can go to:




The latter has a great tutorial as well.

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I would advise you to get as much information as possible about the diamonds you're considering. "Seeing" them live and in person is obviously the best way, but in cases where this is not possible, a comprehensive set of reports and photo's is the way to go.


1. Lab Report, (GIA is the Best) or AGS,

2. Cut analysis from either a Sarin report or Megascope report,

3. Photo's with various magnification and illumination

4. Light Performance analysis such as provided by the Brilliancescope (www.gemex.com).


Any vendor can "talk the talk", claiming that their diamond is the best; it is quite another matter to be able to back up the "talk" with the "walk" by actually supplying quantitative and qualitative results to demonstrate that to be the case.


Do your homework, in the same way as if you were embarking to buy a house or car.

A thorough Engineer's report in the former, and Consumer Reports, Car & Driver in the latter are probable requisites that you would obtain before making your decision.


Buying a diamond should be no different.


Good Luck.

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