**HCA >2.0, but still performs?**

[Garry H (Cut Nut)]

Sure there are diamonds over 2 hca that are nice performers.
When you get over 2 the lower half % and resulting angles become even more critical.
There is a sharp drop off at pavilion angles of 41.4+ even with nice looking IS/ASET images because of color retention.
The hca only looks at pavilion main averages(badly rounded ones if from GIA report) it does not consider the lowers in assigning the grade.

More info on lower halves being critical here:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

ABSOLUTELY! Knowledge of lower half angles and length is *crucial* as well as knowing the variances. The reason Karl says this is because the lower half angles are cut steeper than the pavilion mains by default. The steeper the main angles the steeper the lower halves and they will be the first facets on the pavilion to suffer leakage. As Garry pointed out in another recent thread and posted an ASET of a GIA Ex gives a perfect demonstration of this.

Rhino

For a diamond with a tad bit shallower crown angle of 33, how will it affect the extent of fire/dispersion? I have been told that the brillance and fire of the external and internal reflections will inrease in intensity but as a trade off, there will be less dispersion/fire scintillations than a diamond with a higher crown angle like 34.5. What is your opinion on that?

It is a bit like saying this navel size is better than that one.
If the pavilion angle is around 41, a touch higher, the stone will be very hard to discern from one with 34.5 and 40.8.
But as a rule as crown angle goes down, table size goes a bit too large - try to keep it below 58%.

 

[karsa]

aahhh i see your point. crown angle of 33 with pavillion angle of 41, like 34.5 crown angle to 40.8 pavillion angle (even though the difference between crown angle and pavillion angle may not be exactly the same but keeping within table size of 5

On a different note, I believe I should purchase for myself an ASET viewer and an Idealscope.

 

[Paul-Antwerp]

True, Garry, the rounding of averages on GIA-reports is another problem.

I am just wondering, if you are going to add a bonus/penalty for symmetry, where are you going to get the data necessary to enter?

Live long,

I am not getting the info from anywhere Paul. users are inputting their own data.
I bet most will get it from a grading report.
I think you can remember the diamond I bought once that had fair H&A's patterns, but had GIA Good symmetry?
It might not be perfect, but I can not change that.

Am I understanding correctly that you are adding a bonus/penalty for lab-graded symmetry?

 

[Garry H (Cut Nut)]

aahhh i see your point. crown angle of 33 with pavillion angle of 41, like 34.5 crown angle to 40.8 pavillion angle (even though the difference between crown angle and pavillion angle may not be exactly the same but keeping within table size of 5

On a different note, I believe I should purchase for myself an ASET viewer and an Idealscope.

For every increase or decrease in crown angle of 0.5 degree, an opposite decrease or increase in the pavilion angle of 0.1 degree provides a compensation to maintain similar optical performance across a rather wide variance.
http://diamond-cut.com.au/03_inverse_relationship.htm shows a variance from 30 to 36.5 for crown angles.

 

[Garry H (Cut Nut)]

Am I understanding correctly that you are adding a bonus/penalty for lab-graded symmetry?

That is exactly what I have mentioned a few times Paul. Except for H&A's which will need to be a user based decision.

 

[karsa]

aahhh i see your point. crown angle of 33 with pavillion angle of 41, like 34.5 crown angle to 40.8 pavillion angle (even though the difference between crown angle and pavillion angle may not be exactly the same but keeping within table size of 5

On a different note, I believe I should purchase for myself an ASET viewer and an Idealscope.

For every increase or decrease in crown angle of 0.5 degree, an opposite decrease or increase in the pavilion angle of 0.1 degree provides a compensation to maintain similar optical performance across a rather wide variance.
http://diamond-cut.com.au/03_inverse_relationship.htm shows a variance from 30 to 36.5 for crown angles.

Thanks for the clarification. Inverse relationship it is.
In terms of the proportions of a diamond, if the table % of a diamond is 54, what overall depth % would, in your opinion, bring out the ideal balanced distribution of brillance and fire/dispersion in a diamond? Is there a mathematical relationship between depth and table size, with crown angle and pavillion angle being constant?

 

[Garry H (Cut Nut)]

aahhh i see your point. crown angle of 33 with pavillion angle of 41, like 34.5 crown angle to 40.8 pavillion angle (even though the difference between crown angle and pavillion angle may not be exactly the same but keeping within table size of 5

On a different note, I believe I should purchase for myself an ASET viewer and an Idealscope.

For every increase or decrease in crown angle of 0.5 degree, an opposite decrease or increase in the pavilion angle of 0.1 degree provides a compensation to maintain similar optical performance across a rather wide variance.
http://diamond-cut.com.au/03_inverse_relationship.htm shows a variance from 30 to 36.5 for crown angles.

Thanks for the clarification. Inverse relationship it is.
In terms of the proportions of a diamond, if the table % of a diamond is 54, what overall depth % would, in your opinion, bring out the ideal balanced distribution of brillance and fire/dispersion in a diamond? Is there a mathematical relationship between depth and table size, with crown angle and pavillion angle being constant?

Not that easy. Girdle thickness variance etc. but at 54% using Tolksowsky C&P, with a medium GIA girdle, for a 1ct stone - the answer would be about 62.4%

 

[karsa]

aahhh i see your point. crown angle of 33 with pavillion angle of 41, like 34.5 crown angle to 40.8 pavillion angle (even though the difference between crown angle and pavillion angle may not be exactly the same but keeping within table size of 5

On a different note, I believe I should purchase for myself an ASET viewer and an Idealscope.

For every increase or decrease in crown angle of 0.5 degree, an opposite decrease or increase in the pavilion angle of 0.1 degree provides a compensation to maintain similar optical performance across a rather wide variance.
http://diamond-cut.com.au/03_inverse_relationship.htm shows a variance from 30 to 36.5 for crown angles.

Thanks for the clarification. Inverse relationship it is.
In terms of the proportions of a diamond, if the table % of a diamond is 54, what overall depth % would, in your opinion, bring out the ideal balanced distribution of brillance and fire/dispersion in a diamond? Is there a mathematical relationship between depth and table size, with crown angle and pavillion angle being constant?

Not that easy. Girdle thickness variance etc. but at 54% using Tolksowsky C&P, with a medium GIA girdle, for a 1ct stone - the answer would be about 62.4%

If that is the case, my depth % of 61.9 should not be too far off from 62.4 i hope.
This might be out of your way, but i would really like to have your proffessional opinion on this
particular diamond, in regards to the tiny feather that is just beneath the table on the arrow (due to head obstruction) which is visible as the diamond rotates:
http://www.jamesallen.com/loose-dia...-f-color-vs2-clarity-excellent-cut-sku-233539

I am concerned about the visual aspect of the diamond being possibly not eye clean due to the feather as well as the feather possibly being easily identified under a loupe. Based on the information that i have gathered i have a certain assumption in mind but i would like your feedback to know what you think having this tiny feather at its current location will mean for the visual look of the diamond.
I appreciate your input.

 

[Garry H (Cut Nut)]

aahhh i see your point. crown angle of 33 with pavillion angle of 41, like 34.5 crown angle to 40.8 pavillion angle (even though the difference between crown angle and pavillion angle may not be exactly the same but keeping within table size of 5

On a different note, I believe I should purchase for myself an ASET viewer and an Idealscope.

For every increase or decrease in crown angle of 0.5 degree, an opposite decrease or increase in the pavilion angle of 0.1 degree provides a compensation to maintain similar optical performance across a rather wide variance.
http://diamond-cut.com.au/03_inverse_relationship.htm shows a variance from 30 to 36.5 for crown angles.

Thanks for the clarification. Inverse relationship it is.
In terms of the proportions of a diamond, if the table % of a diamond is 54, what overall depth % would, in your opinion, bring out the ideal balanced distribution of brillance and fire/dispersion in a diamond? Is there a mathematical relationship between depth and table size, with crown angle and pavillion angle being constant?

Not that easy. Girdle thickness variance etc. but at 54% using Tolksowsky C&P, with a medium GIA girdle, for a 1ct stone - the answer would be about 62.4%

If that is the case, my depth % of 61.9 should not be too far off from 62.4 i hope.
This might be out of your way, but i would really like to have your proffessional opinion on this
particular diamond, in regards to the tiny feather that is just beneath the table on the arrow (due to head obstruction) which is visible as the diamond rotates:
http://www.jamesallen.com/loose-dia...-f-color-vs2-clarity-excellent-cut-sku-233539

I am concerned about the visual aspect of the diamond being possibly not eye clean due to the feather as well as the feather possibly being easily identified under a loupe. Based on the information that i have gathered i have a certain assumption in mind but i would like your feedback to know what you think having this tiny feather at its current location will mean for the visual look of the diamond.
I appreciate your input.

If you want an diamond with no inclusions visible under a loupe then you need a flawless or internally flawless diamond.
The feather is the second mentioned. The cloud is the main grade maker - so ask the vendor rep for an opinion on the impact of the cloud?

 

[karsa]

Thanks again for your feedback I have decided not to go ahead with this diamond, because as you said, it is not realistic for me to assume the feather would not be visible under loupe.

 

[Christina...]

Thanks again for your feedback I have decided not to go ahead with this diamond, because as you said, it is not realistic for me to assume the feather would not be visible under loupe.

Clarity grading is all done under 10x magnification. In order to purchase a stone that is loupe clean you will have to purchase an IF or FL stone. Is clarity a 'mind clean' issue for you?

 

[msop04]

Thanks again for your feedback I have decided not to go ahead with this diamond, because as you said, it is not realistic for me to assume the feather would not be visible under loupe.

Clarity grading is all done under 10x magnification. In order to purchase a stone that is loupe clean you will have to purchase an IF or FL stone. Is clarity a 'mind clean' issue for you?

by karsa » 01 Sep 2013 13:09
As a matter of fact, when i mean visibly eye clean, i mean if i were to rotate this diamond in various tilt angles 360 degrees, just the way JA video shows, i would not be able to see even the slightest hint of a feather by just looking at it from 3 inches away as well as if i were to use a loupe that i would only see an extremely miniscule faded white pinpoint in the diamond as i rotate it around in various angles.

I have asked JA and they said it was eye clean, but i am not quite certain if that is truly the case.

karsa,

Based on what you posted in another thread (above) as your definition of "eye-clean," I think you may have a misunderstanding or at least unrealistic expectations of what eye-clean is... It literally means you will not see any noticeable inclusions using only your eyes -- not with the help of a 10x loupe.

Quite honestly, I think you may be wasting your time (as well as the vendors' time) by looking at VS (and even VVS) if you need to barely be able to see "an extremely miniscule" anything with a loupe. That's totally okay if you want your stone to be that clean -- it's your preference, after all -- but you need to start searching for flawless stones if this is the case. Otherwise, you may continue to be disappointed in your search results.

 

[karsa]

Thanks again for your feedback I have decided not to go ahead with this diamond, because as you said, it is not realistic for me to assume the feather would not be visible under loupe.

Clarity grading is all done under 10x magnification. In order to purchase a stone that is loupe clean you will have to purchase an IF or FL stone. Is clarity a 'mind clean' issue for you?

I have actually decided to go with either a vvs2 or vvs1. The magnified images that are on many of the vendors are actually showing up on my screen as 10x magnified, so the fact that i could see the inclusions in those images, especially feathers, means that under a loupe i will definitely see it. Thus, going for a diamond where the inclusions are non-visible in that image is what i will be going for. Ofcourse, going up to IF or FL would be ideal but since I have the magnified view of the diamond, I will use that as my tool to choose a vvs1 or vvs2 or even a vs1 which has no obvious inclusions which would bother me in that image. Again, that image is what i would see with a loupe.

To your question, "is clarity a 'mind clean' issue for you?", yes i tend to have very strict standards as to what kind of inclusions i am willing to live with in a diamond which is something I am going to give to my partner, which to many individuals, the kind of inclusions I am concerned about is of no consequence or irrelevant as long as its eye clean (without a use of a loupe). If the diamond was for myself, I would not care that much about the clarity or even color.

For myself, I am happy with an SI1 or S12 in I or J color with an excellent cut

 

[karsa]

Thanks again for your feedback I have decided not to go ahead with this diamond, because as you said, it is not realistic for me to assume the feather would not be visible under loupe.

Clarity grading is all done under 10x magnification. In order to purchase a stone that is loupe clean you will have to purchase an IF or FL stone. Is clarity a 'mind clean' issue for you?

by karsa » 01 Sep 2013 13:09
As a matter of fact, when i mean visibly eye clean, i mean if i were to rotate this diamond in various tilt angles 360 degrees, just the way JA video shows, i would not be able to see even the slightest hint of a feather by just looking at it from 3 inches away as well as if i were to use a loupe that i would only see an extremely miniscule faded white pinpoint in the diamond as i rotate it around in various angles.

I have asked JA and they said it was eye clean, but i am not quite certain if that is truly the case.

karsa,

Based on what you posted in another thread (above) as your definition of "eye-clean," I think you may have a misunderstanding or at least unrealistic expectations of what eye-clean is... It literally means you will not see any noticeable inclusions using only your eyes -- not with the help of a 10x loupe.

Quite honestly, I think you may be wasting your time (as well as the vendors' time) by looking at VS (and even VVS) if you need to barely be able to see "an extremely miniscule" anything with a loupe. That's totally okay if you want your stone to be that clean -- it's your preference, after all -- but you need to start searching for flawless stones if this is the case. Otherwise, you may continue to be disappointed in your search results.

Yes I tend to have quite high 'eye clean' standards and not seeing obvious inclusions under 10x magnification like feathers, black crystals, clouds, would be part of my standard. However, I have clarified to myself my expectations in regards to clarity so everything is in order.