H&A "Ideal" leakage? Can somone explain this!

[fiftysevenfacets]

Greetings my good friends of PS!

I had this experience yesterday that I would like to share and see if somone can explain!

I went to my B&M establishment that I''ve visited a few times this past month here in Toronto (Canada), I have a stone that I''ve been eyeing for a while now but when I went yesterday I asked to see an Ideal cut vs. an excellent cut GIA that I''ve been interested in, This new stone happned to be a Gemscan so I was real curious (& wary) to see what the diamond would look like. So we had both diamonds on the table and then I placed them both between my fingers, The first thing that I noticed was the Ideal diamond that is an Ideal showed the following (hope this makes sense) , around the table there was a star formation almost like arrows but it was completely see through, kinda like a window or glass, i could see all the way to the bottom of my finger there was no light coming back from this formation...........

But here is the kicker, when he took the diamond and placed it in the H&A viewer it showed a perfrect H&A view (Perfect is subjective but read on)........and the bigger kicker, when I placed the GIA excellent diamond it doesn''t form H&A or anywhere close to the Ideal one but yet the GIA excellent doesn''t show any light leakage.

 

[JulieN]

"H&A Ideal" isn''t a regulated designation. You may find some so called "H&A ideals" that would not be considered to be so by PS standards.

 

[tonyc2387]

from what I understand, H&A appear as a result of optical symmetry of the facets... when each facet is perfectly aligned with the one on the opposite side of the diamond. leakage, on the other hand, primarily results from non-ideal crown & pavilion angles... so it seems that, in rare cases, the angles could be bad but the facets could be lined up well enough to produce H&A. I also have no idea why a cutter would take the time to produce H&A on a not-ideally-proportioned rock, but it could happen.

 

[FB.]

H&A should be used to refer to stones with outstanding symmetry.

Ideal cut should be used for stones with optimum angles.

Ideal cut with H&A has both outstanding symmetry AND optimum angles, which would be expected to give an extra-special sparkle.

Having one does not guarantee the other, nor does it guarantee a good light-reflection performance from the stone. However, it is more common to see H&A in good stones than in bad ones.

But you could theoretically have a stone with GIA cut grade "poor" and polish grade "poor", but it could still have H&A symmetry. But the H&A would have little beneficial effect on a stone that had angles that were too steep or too shallow.

 

[fiftysevenfacets]

Sorry if I might have created some confusion with the subject line; but the H&A is what I used to describe what I saw in the viewer, not what anyone assigned to it as a cut.

Ok so what I gather from here is that the H&A viewer reflects the type of symmetry.

I was under the impression that the H&A determines leakage from the diamond...and that is why I asked the question.

 

[FB.]

No, H&A is not intended to measure leakage or light return, but you might notice some. H&A is for symmetry.
Likewise; IS/ASET is not intended to measure symmetry, but you might notice some. IS/ASET is for light performance.



I should add; "ideal" cut is a very broad range of proportions. Definitions of ideal vary between different cut grading entities and even within different Pricescope members.

Look up "steep deep" and you will see examples of stones that masquerade as ideal, but suffer from light leakage due to incorrect pairing of crown and pavilion angles (which allows the cutter to burden the stone with extra weight but still get a high cut grade "on paper"). I'd wager that what you saw was a "steep/deep" H&A, or that the cut grade was awarded by a second-rate lab.

 

[Rhino]

Here is what you''re talking about.

H&A imagery....

 

[Rhino]

Blatant leakage on the pavilion shown through DiamXray. Under an ASET with black background the leakage is more friendly.

It is important not to confuse Optical Symmetry with Light Performance.