Photographic Proof, AGS NOT EQUAL to H&A

[JohnQuixote]

Date: 2/21/2005 4:54:10 PM
Author: Rhino

I can sympathize with your pains Wink. We''ve called in many stones listed on the wholesale search engines as H&A''s only to be sorely disappointed as well.

Excellent thread btw. Good to see all the regs comin out.

Sir John,

Yes ... there should absolutely be H&A standards however I would certainly not limit the minor facets to any one standard. I have not shared this in a bit but my personal tastes have evolved over time regardingh what standards I like in H&A''s.

1. Firstly the diamond has to fall within very cherry dimensions on the main facets.
2. In direct light conditions I prefer H&A''s of the longer star/lower girdle type (not too long mind you). Plainly, they give off more fire and scintillation. Lower girdles in the 77-80% length range combined with stars in the upper 50''s mid 60''s. Upper girdle angles anywhere between 36-39 degrees for light return or 40-43 degrees for contrast.
3. In diffuse light conditions I prefer H&A''s of the shorter star/lower girdle combo. 75-76% lower girdle length with shorter stars. Again ... as long as the upper girdles don''t exceed 43 or 44 degrees. This produces a slightly bolder arrow which stands out more in those light conditions providing points of contrast.

Nice summary. By the way, I would add that with the shorter star/lower girdle combo we’ve found it is easier to treat the UG so as to limit light leakage. This trades off some contrast for DCLR in the character, but does not take away from overall performance.

Regarding minor facets & H&A''s. There is only one minor facet metric that can disrupt the H&A phenomena and those are the lower girdles. Pull them too long (greater than 80% length) and the clefts in the hearts become too noticeable. If they fall shorter than 75% the seperation between the Hearts and the cleft beneath them is not discernible (making for one big white pointed blotch on the bottom). While those are factors that can disrupt the H&A pattern, you can still maintain *perfect* optical symmetry but just not with a pattern that is recognizable by most. In our lab we have H&A''s that cover just about the entire spectrum. There are people who do like very long lower girdles (very skinny arrows) as they are generally very scintillating stones with many smaller flashes while the opposite end of the spectrum results in less scintillation but broader flashes of light. The best balances generally fall in between of course.

What an excellent teaching, Rhino.

In a H&A grading world I think the major proportions could be a given a cherry range as you suggest, but with regard to precise patterning and minor facet construction I seriously doubt John Q Public will need to slice and dice those particulars. So until then, how about use of H&A imagery to judge trueness of patterning and a degree of minor facet construction? Just as IdealScope is commonly used now, H&A fans can learn to interpret what is seen in the viewer.

Have you seen Brian’s presentation from the International Diamond Cut Conference (it’s in the notes you have)…You are seeing eye-to-eye with much of his assessment about the minors. Take a look at his photo essay on minor facets and identifying when lgf% is too long (8% rule).

You brought up the dangers of lower girdles too long or too short. These can be gauged visually. Too long is obvious as splits in the clefts. Too short and the hearts do not separate from the arrow shafts above… I will attach photos for the others on board here.
Of course, offered in this manner it would not be a precise science, but neither is IdealScope (yet).

 

[JohnQuixote]

The next photos are for the cut cadre following the discussion. Pavilion views of stones with given true patterning:

1. Lower Girdles at 82% (resulting arrows will be very skinny - small flashes). You can tell the LGF are long by the clefts in the hearts.

 

[JohnQuixote]

2. For the cut cadre... Lower Girdles at 75% (resulting arrows will be thick - broad flashes). You can tell they are short because the hearts do not separate from the arrowshafts above... A white "blotch."

 

[JohnQuixote]

3. For the cut cadre... Lower Girdles at 78% (resulting arrows will be mid-sized - a visual balance of qualities). No significant clefts in hearts and hearts separate neatly from the arrowshafts above.

 

[WinkHPD]

Will there be a quiz? Gosh I hope not...

That was certainly informative to me about the shaping of the hearts, I learned my new thing today!

Thank you!

Wink

 

[Garry H (Cut Nut)]

You better order DiamCalc Wink.
You can not play this game without it
You can buy the download for a single computer here from Leonid on Pricescope for $280, or the version that can be convenienly moved form computer to computer with a hasp usb key from me on ideal-scope.com for $320 plus shipping.

 

[valeria101]

Date: 2/21/2005 1:10:59 PM
Author: Garry H (Cut Nut)

Leonid and I have discussed a pricescope convention.
Anyone interested?

Yes Sir! You''ve got one more fan here

It would be great to hear you guys, of course. And finely tuned diamonds of Autumn colors sound very appealing if anything.

 

[codex57]

Whew, after seeing those pics, I feel a hell of a lot better about my non-H&A ideal cut stone. I''m really, really surprised that was an ideal grade stone.

 

[JohnQuixote]

Codex, these images illustrate differences in LGF percentages which have no influence on ideal versus non-ideal grade (not with current systems). The visual difs we're describing assume proven ideal proportions and good patterning.

If you have a Sarin of your diamond showing minor facet construction - a more complex Sarin than conventionally shown - you can interpret what your LGFs look like compared to the above images.

 

[WinkHPD]

Date: 2/20/2005 9:48

4 PM
Author: JohnQuixote
Not to be greedy... But do you have the pavilion image through H&A viewer?

But of course, now that you have taught me how to take them...

From here it is a LOT easier to see that this is NOT H&A, the Arrows were close, these are NOT!

Wink

 

[JohnQuixote]

Diamonds cut to the other limits of AGS0 do have issues - such as the ones in and around this no-go zone.

The 41.3 p angle was a clue that pavilion patterning might not be great, but this is still far out enough to be lunar. Significant yaw and entire patterns fail to appear. Woof.

This is an AGS0. That means it received a grade of ideal in symmetry. Does this look ideally 'symmetrical' to you?

The big lesson here is what lab graded symmetry is, as opposed to physical/optical patterning (Hearts & Arrows) type symmetry. Better patterning would have improved this stone.

Another lesson is that good arrows naturally result from good pavilion patterning - but its not necessarily true the other way around. You can have nice arrows and the hearts can be a mess.

 

[aljdewey]

Date: 2/28/2005 5:47:40 PM
Author: JohnQuixote
Diamonds cut to the other limits of AGS0 do have issues - such as the ones in and around this no-go zone.

The 41.3 p angle was a clue that pavilion patterning might not be great, but this is still far out enough to be lunar. Significant yaw and entire patterns fail to appear. Woof.

This is an AGS0....

I''d be curious to know how this stones makes AGS0 when the pavilion angle is beyond the parameters.

AGS0 specifies pavilion angle is between 40.15 and 41.2.......so how does this stone make AGS0 with a *41.3* pavilion?

 

[JohnQuixote]

Hi Alj,

AGS0 pavilion angle used to run to 40.5-41.5. This diamond was likely graded before the change. Re-grading it would put it outside 0. Of course, Wink can just wait until the NEW grading system comes out and see where it is

 

[Maxine]

Are new grades out?? what are they, then?

 

[JohnQuixote]

Not yet, Maxine.

They will begin grading square princess cuts soon ("first quarter of 2005").

New grading system for rounds will follow later this year...New subcategories now will include light performance, proportion factors and finish.

http://www.ags.org/consumers/enews/index.asp

 

[WinkHPD]

Date: 2/28/2005 8:26:10 PM
Author: JohnQuixote
Hi Alj,

AGS0 pavilion angle used to run to 40.5-41.5. This diamond was likely graded before the change. Re-grading it would put it outside 0. Of course, Wink can just wait until the NEW grading system comes out and see where it is

What, and pay perfectly good money to downgrade my stone???

I appreciate the insite that you are offering John, I wanted to see what some of the experts would have to say about this, and to bring to focus that many AGS o stones are not all that we would like them to be!

Funny thing is, this is a beautiful stone, but I am betting it could be even more beautiful were it cut just a little bit closer to what it should have been!

Wink

Wink

 

[Garry H (Cut Nut)]

AGs have published one 55% table size round chart - there is a whole thread or 2 with it from November ish.

A few manufacturers and Cut geeks have full copies of the new round and princess standards.
Ther is an atricle about the princess''s in the journal section - lower left of the home page.

A stone with an old 41.3 (possibly not the angles fromAGS''s Sarin?) would get an even lower score with the new system.

 

[JohnQuixote]

Date: 3/1/2005 9:59:17 AM
Author: Garry H (Cut Nut)

A few manufacturers and Cut geeks have full copies of the new round and princess standards.

Is it the cutting guidelines you're talking about? If so, here is a thread Rhino started to discuss them, but that CD is not to be confused with grading guidelines.

And...if you ARE talking about grading guidelines, please tell me where to find them!