Hearts and meet point symmetry as GIA grades it? Discussion.

[yssie]

In this RT thread ([URL='https://www.pricescope.com/community/threads/round-brilliant-purchase-idealscope.150750/page-2']https://www.pricescope.com/community/threads/round-brilliant-purchase-idealscope.150750/page-2[/URL]) this discussion took place:

Ditto.

people refer to "perfect hearts & arrows", but what if there are no hearts and arrows at all?
I specified "near H&A" for exactly this reason - some people do not like the 'organized' look of arrows, and prefer a completely random pattern. GIA does not consider hearts when grading, but to get a very random pattern the physical (facet meet-point) symmetry must also be non-perfect, which will lower the symmetry grade given - which is fine, if that's the look you like!

Just wanted to add that to get no pattern, the symm grade would need to drop, probably to a G, and then GIA will down grade the cut grade to a grade above the symm grade.

I have no idea what this assessment is based upon, and strongly disagree. I see no necessary connection between the lab-graded symmetry-grade (physical symmetry) and the absence of pattern. Yssie and SC, I think that you are both off.

Live long,

Either its miscommunication or misconception, but Paul is right, you can have Excellent meet point and "external" symmetry, which is what GIA grades on their report and still not come close to hearts and arrows optical symmetry. (very common)
This, yes

You can also have hearts and arrows optical symmetry and still get meet point symmetry of very good (much much less common).

I'd like to discuss CCL's second comment more - which mirrored Paul's earlier statement.

I am using these two articles as references:
http://www.gia.edu/diamondcut/pdf/polish_and_symmetry.pdf
http://www.wtocd.be/DiamondInfo/articlesPDF/Article4_Formation_of_HA.pdf



My question: how can you have excellent optical symmetry with with poor meet-point symmetry?

The first article describes symmetry as GIA grades it, w/ diagram examples of the sorts of things GIA will downgrade symmetry for.
The second article describes how hearts and arrows are cut.

As I see it, if the physical culet is off-centre, no perfect hearts. If the eight sections of diamond aren't all exactly equal (main sizes are different & assymetric, star facets are different/assymetric, upper girdle facets are different/assymetric....), no perfect hearts because the pavilion mains and pavilion halves are of different sizes/at different angles to each other, and no perfect arrows made opposite each other at the same time.

So to create the phenomenon of optical symmetry that manifests as perfect hearts, one is still cutting the physical stone and working with the given physical dimensions, and if the physical dimensions are off enough there's nothing to work with..

What is tmy missing link?

 

[ChunkyCushionLover]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

Yssie,

The problem is in the definition of acceptable "hearts" and in the number of factors GIA or AGSL uses to arrive at the final external physical symmetry grade. I tend to prefer the definition of and grading of Hearts and Arrows by HRD on the subject. HRD_Hears)and_Arrows Even the most "superideal" round vendors here offer diamonds with minor deductions from perfect hearts and arrows some much more so than others from the same vendor.

Although uncommon a diamond may receive a Very Good symmetry grade by GIA and still have close to near perfect optical symmetry and display passable "hearts and arrows" depending on your definition. Missing a meetpoint or several in some cases may not have a dramatic impact on optical symmetry.

GIA may also downgrade the external symmetry grade from Excellent to Very Good for several Proportion based deviations like girdle thickness variation and crown angle variation. The reasons for a symmetry grade downgrade by GIA are not disclosed and they may be unrelated to the pavilion and thus not easily seen in the hearts image.

 

[Garry H (Cut Nut)]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

As I see it, if the physical culet is off-centre, no perfect hearts. If the eight sections of diamond aren't all exactly equal (main sizes are different & assymetric, star facets are different/assymetric, upper girdle facets are different/assymetric....), no perfect hearts because the pavilion mains and pavilion halves are of different sizes/at different angles to each other, and no perfect arrows made opposite each other at the same time.



What is tmy missing link?

Wrong.

Yssie and anyone interested, please read all of this - about 12 pages in total.
http://www.gemology.ru/cut/english/symmetry/6.htm

I have been linking to this page and I know that very few people have read the entire article.
It is profound.

The stone on that page recieved GIA Good for symmetry, but while some may not like the particular H&A's pattern - the fact is it is quite optically symmetrical. There were no meet point issues that several gemmoloists could find.

The development of these standards evolved from different basis with different technologies changing or adding new rules as time went on - and with different evoloution as you can see in America, Europe and Russia.

 

[Karl_K]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

the missing link is they are grading different things about the same objects.
Lets take a knife blade, the blade can be strait and not sharp or crooked and sharp or any combination of the 2.
A to strait blade may be less sharp than one with some crookedness.

back to diamonds:
Remember they are grading different things in different ways.
One is graded that if an issue isn't viable at 10x it doesn't exist.
The other is if the effect isn't seen in an h&a viewer it doesn't exist.
There are millions of possible things about any diamond that can make both of those statements true some of which contradict each other some that compliment each other. There are just as many that could make it false about any given diamond.

Now read the article Garry posted 4 times :}

 

[stone-cold11]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

Several questions regarding the stone in the report.

Stone is self centering? How would you go about aligning the stone in the H&A viewer with the crown and pavilion in a different orientation? The center of mass would have change, and simple tapping I do not think would work. Hearts image is even more difficult I believe as the stone now cannot be simply be place flat on the surface and level with the base of the viewer on the surface?

Another question is how would one cut to break down the main pavilion reflection into splintery look, without going with a larger lower half, and still achieve Ex in symm grade? Is that possible?

 

[ChunkyCushionLover]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

As I see it, if the physical culet is off-centre, no perfect hearts. If the eight sections of diamond aren't all exactly equal (main sizes are different & assymetric, star facets are different/assymetric, upper girdle facets are different/assymetric....), no perfect hearts because the pavilion mains and pavilion halves are of different sizes/at different angles to each other, and no perfect arrows made opposite each other at the same time.



What is tmy missing link?

Wrong.

Yssie and anyone interested, please read all of this - about 12 pages in total.
http://www.gemology.ru/cut/english/symmetry/6.htm

I have been linking to this page and I know that very few people have read the entire article.
It is profound.

The stone on that page recieved GIA Good for symmetry, but while some may not like the particular H&A's pattern - the fact is it is quite optically symmetrical. There were no meet point issues that several gemmoloists could find.

The development of these standards evolved from different basis with different technologies changing or adding new rules as time went on - and with different evoloution as you can see in America, Europe and Russia.

Garry,

"d) Snapshots of the diamond made by means of a “Hearts and Arrows viewer” device, which demonstrate perfect «hearts and arrows» patterns."

Two things I think should be clarified in that article.

First the hearts are not perfect otherwise their would be no deviation in the Mains(middle red regions), LGFs(distance between base of heart and heart) or UGF(shape of the shoulder of the heart).

The optical symmetry is better than the physical external symmetry as graded by GIA, but is far from perfect.

Second: "Hearts and Arrows" is an appearance related to optical symmetry, but it is only a narrow range of near tolk diamonds with near perfect optical symmetry that display this look. Once one strays outside of near tolk parameters diamonds can have perfect optical symmetry and no longer exhibit a hearts and arrows pattern. The range for LGL length is really narrow depending on your definition of hearts and arrows but its somewhere around 72.7%(shorter not enough seperation between base and heart) - 77.5(longer a cleft in the hearts). For HRD the minnimum seperation makes the LGL range more like 74.5% - 77.5%.

 

[Garry H (Cut Nut)]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

CCL the point to that stone is not that it is perfect H&A's.

It is even an off topic example.

I highlighted it because of Yssie's comment about off centered culet. The most accurate term is tilted table - but I never heard of any lab reporting that?

And if the table is tilted by 1 degree then there is no problem to take a photo or see a H or A pattern thru a viewer.

Even when we knew why GIA dinged this stone, it was next to impossible to see the tilt with an ideal-scope and the stone in tweezers.

 

[yssie]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

Thanks for the input CCL, Karl, SC, Garry, and Garry I'm knee deep in that article and have several questions & comments I will post when I'm through..

 

[ChunkyCushionLover]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

CCL the point to that stone is not that it is perfect H&A's.

It is even an off topic example.

I highlighted it because of Yssie's comment about off centered culet. The most accurate term is tilted table - but I never heard of any lab reporting that?

And if the table is tilted by 1 degree then there is no problem to take a photo or see a H or A pattern thru a viewer.

Even when we knew why GIA dinged this stone, it was next to impossible to see the tilt with an ideal-scope and the stone in tweezers.

Garry,


Attach the .gem file please for example 1. To me in the photographed images of example 1 the arrows and idealscope images I see assymetry, some arrows are longer than others.

This is the problem I see over in RT, someone may say its just the image was taken tilted but we know this is not the case at all.

But really that example is arguing standards and semantics, so if this received Finish Symmetry of Very Good would that be consistant with the optical symmetry?

 

[Garry H (Cut Nut)]

Re: Hearts and meet point symmetry as GIA grades it? Discuss

CCL the point to that stone is not that it is perfect H&A's.

It is even an off topic example.

I highlighted it because of Yssie's comment about off centered culet. The most accurate term is tilted table - but I never heard of any lab reporting that?

And if the table is tilted by 1 degree then there is no problem to take a photo or see a H or A pattern thru a viewer.

Even when we knew why GIA dinged this stone, it was next to impossible to see the tilt with an ideal-scope and the stone in tweezers.

Garry,


Attach the .gem file please for example 1. To me in the photographed images of example 1 the arrows and idealscope images I see assymetry, some arrows are longer than others.

This is the problem I see over in RT, someone may say its just the image was taken tilted but we know this is not the case at all.

But really that example is arguing standards and semantics, so if this received Finish Symmetry of Very Good would that be consistant with the optical symmetry?

That was maybe 7 years ago - no idea where the file is.
The point is with a loupe or a miscroscope or any normal lab tool- the stone appeared ok, and even with a H&A's viewer the hearts looked OK.
The symmetry was Good. Cant remeber the polish.