How important are symmetry/polish??

[bennyboy96]

Looking to buy a 1.1-1.24 Princess H-I VS2-SI1. Was hoping for VG-EX on both symmetry/polish but see that I can save $ or get a bigger stone if I get Good in both Sym and Pol or at least one. How important is Symmetry and Polish on Princess cuts? Is there a big difference between Good and VG? If I have to compromise and get Good in either Sym or Pol, which one should it be?
Thanks!
Ben

 

[JohnQuixote]

Ben,

Actually GIA recently concluded that there is negligible visible difference between G, VG and EX in sym/pol. Bear in mind that this is on GIA grading reports: G on certain other lab reports may not be as strict as GIA G.

 

[Garry H (Cut Nut)]

Slight correction Sir John

GIA will allow VG and EX in their top grades - they found naked eyed experts could sometimes detect lower sym in Good and lower.

AGS were including Ideal and ex in their AGS 0 grades, but now they are not - only Ideal sym and polish will get AGS 0. Peter Yantzer has told me that he personally can not tell the difference - but i think AGS are looking at the issue as a ''standard'' of excellence they wish to uphold.

 

[JohnQuixote]

Date: 4/20/2005 4:15

4 AM
Author: Garry H (Cut Nut)
Slight correction Sir John

GIA will allow VG and EX in their top grades - they found naked eyed experts could sometimes detect lower sym in Good and lower.

AGS were including Ideal and ex in their AGS 0 grades, but now they are not - only Ideal sym and polish will get AGS 0. Peter Yantzer has told me that he personally can not tell the difference - but i think AGS are looking at the issue as a 'standard' of excellence they wish to uphold.

Garry - I was citing information you presented in your review of the foundation of GIA'cut grading 4 months ago (I'm including the graphic discussed by several of us in the follow-up thread.)

I assume from your correction here that GIA has changed position since you first presented this? Any other updates?

Thanks,

 

[Garry H (Cut Nut)]

Good point John. I re read the damm article.
Will you be the one to tell Brian he may as well slash his wrists?

The G&G foundation article is vera vague on this issue.
Page 224 - upper left in the topic "Design and Craftsmanship" - Finish - says the trade want the traditional grades for sym and pol used.
"Lower qualities of either can bring a diamond grade down (again, see the pull out chart....) Note, however, that unlike other traits, there is not a direct correlation between a finish grade and an overall cut grade (e.g., a diamond with a "Very Good" finish may recieve a top grade)."

In fact all 3 examples of the top grade (as i predicted it is Excellent) are VG VG, VG VG , VG VG.

In the second top - Very Good grade there are 2 of the 3 examples that are noted that they are downgraded for having "Good" polish or P and Sym.

So I guess top grade can be Ex to VG
2nd top can be Ex to VG and there after are probably going to be lined up as common sense might predict.

It is rather amussing that even though I have never been a stallwart for promotion of high levels of symmetry - that I am quoted as one of the new wave adherents promoting "brabnded" diamonds that show near perfect eight-fold symmetry by displaying eight "arrows" in the face-up position ....... when observed with specially designed viewers."

Thier research was poor as they referenced this link http://www.preciousmetals.com.au/ideal-scope.asp accessed june 22nd 2004 - they missed the truly relevant site - www.ideal-scope.com ????????

If you look at the link you will see that both the lessor quality diamonds have very fine symetry. That was not an accident

We are about to update this page - so before we do i will copy the relevant text here - note that while I mention optical symmetry I finish with apretty powerful disclaimer!!!
The Ideal-Scope
Thus was born the Ideal-Scope, an inexpensive hand held instrument now available to both the diamond trade and more importantly the diamond buying public. The Ideal-Scope is a very simple instrument which shows the light return and light leakage in diamonds. When a diamond is cut well it will have very high light return and minimal leakage (producing an overall pink image through the Ideal-Scope). When a diamond is cut poorly there are substantial regions of light leakage (pale pink and white colouration).

Excellent Cut
Fair Cut
Poor Cut

If a stone has significant leakage it cannot appear bright and beautiful; it cannot fulfil the incredible potential for beauty that Diamonds naturally possess.

Strong pink/red indicates strong light return, all over pink means the diamond is returning all the light that is shining into it. White or pale pink shows that light is being lost; the stone is not working effectively. The more light that comes back to you the viewer, the brighter and more eye catching the diamond will be.

Areas of black are also a positive feature. They are a reflection of the shadow you cast through the view hole of the Ideal-Scope. Too much black can be detrimental but a good balance will provide excellent potential for Scintillation (twinkling, sparkle) as well as Fire (flashes of coloured light).

The excellent diamond above has a perfect balance of black, called stars. This is a feature also found in hearts and arrows diamonds. These diamonds are cut to very precise optical symmetry and show a particular arrow/star like pattern through the top and a heart shaped pattern through the bottom. The Ideal-Scope will show arrows if they are present but will not show the hearts pattern, a specialised viewer is needed for this.

Hearts and arrows optical symmetry is a bonus to the cut of a diamond but it is not essential for diamond beauty. Precious Metals carries both Hearts and Arrows and non Hearts and Arrows diamonds and considers all to be ideal cut and desirable.

So Sir John - it seems that symmetry does not matter - and my chart is probably valid in its context - but I have heard (at Basel GemFest? ) other info - and I can not believe they would accept that expert observers can not detect with their naked eye diamonds that have fair or poor sym and polish.

 

[JohnQuixote]

Thanks Sir Garry,

I find that there are a host of other “What the…?…huh?” questions in as well. Don’t limit it to symmetry... and don’t even get me started on this whole ‘rounding to nearest 5%’ of the minors.

I’m not too concerned about the symmetry issue for Brian’s sake, since GIAs grading does not deal with the level of precision he does: Their whole concept of ‘symmetry’ has focused on meet points and indexing. Precise optical/physical alignment like Brian and Paul dedicate themselves to has many more aspects – specific tolerances for minor facet construction, absence of facet yaw, etc.

In my nomenclature I refer to this level of detail as patterning rather than symmetry, since what the labs grade is not so involved.

And yes, it’s amusing that they put you forward like they do…

Maybe they misread your sig as the “ H&A and Ideal-Scope Cut Quality Crusader ”

 

[Paul-Antwerp]

Date: 4/21/2005 1

9:24 PM
Author: JohnQuixote

Maybe they misread your sig as the “ H&A and Ideal-Scope Cut Quality Crusader ”

I do not use the term LOL very often, but at this point in time, it is very appropriate.

This is a very good one, John. Garry must be waking up around now down under, and this is a very good wake-up call.

 

[Garry H (Cut Nut)]

Is 5.22am and time 4 a run

 

[Paul-Antwerp]

Is 9.37 PM and time for a beer.