Numbers Experts - what do you think of this stone?

[jill_s]

I was searching for stones, and I came across this one. I was wondering if some of the numbers experts could chime in on how it will look and perform?

60.8
55
33
40.8
Thin-Med girdle
50% star
80% lower half

It scores a 0.70 on the HCA with X, X, X, VG, but it falls outside the GIA and AGS Excellent cut. Why is that? Any help would be appreciated, just trying to learn more about these angles and numbers and how they all work together! Thanks!

 

[Lorelei]

Date: 7/13/2009 9:36:38 PM
Author:jill_s
I was searching for stones, and I came across this one. I was wondering if some of the numbers experts could chime in on how it will look and perform?

60.8
55
33
40.8
Thin-Med girdle
50% star
80% lower half

It scores a 0.70 on the HCA with X, X, X, VG, but it falls outside the GIA and AGS Excellent cut. Why is that? Any help would be appreciated, just trying to learn more about these angles and numbers and how they all work together! Thanks!

Hi Jill

Could be a nice diamond, do you have any images such as Idealscope? Sometimes good scorers do fall outside the AGS/ GIA bullseye - its not a problem. The diamond might look more brilliant than fiery due to the angle configuration, particularly the shallow crown angle but it could be a good looking diamond.

 

[stone-cold11]

Numbers looks good, slightly on the shallower side, might have some obstruction issue, IS can tell more. More of a brilliant cut than a balance TIC cut.

HCA is made more general, includes stones whose proportions are more suited for pendant and earrings, while GIA/AGS Ex cut are geared towards ring stones, tends towards the upper right range of HCA<2.

 

[Lorelei]

Date: 7/14/2009 5:53:05 AM
Author: Stone-cold11
Numbers looks good, slightly on the shallower side, might have some obstruction issue, IS can tell more. More of a brilliant cut than a balance TIC cut.

HCA is made more general, includes stones whose proportions are more suited for pendant and earrings, while GIA/AGS Ex cut are geared towards ring stones, tends towards the upper right range of HCAquote]
I doubt it with a 40.8 PA, this is more of a risk with shallow shallow combos or shallow pavilion combos, a slightly shallow crown angle should not cause it.

 

[stone-cold11]

Which is why I said ''might'', did I say ''would''?

 

[Lorelei]

Date: 7/14/2009 7:12:18 AM
Author: Stone-cold11
Which is why I said 'might', did I say 'would'?

Yes, I have seen you say this with other combos with a shallower crown and well placed pavilion angle in the past so just pointing out it is unlikely to be an issue.

 

[stone-cold11]

You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

 

[Ellen]

Date: 7/14/2009 7:59:33 AM
Author: Stone-cold11
You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

I wouldn''t say she''s saying that. Just that if you can have a crown that''s leaning slightly shallow, but have a pavilion angle that''s not leaning the same way (balancing things out), obstruction most likely won''t be an issue. I would have to agree. I suppose anything is possible with any stone, but I doubt this stone would suffer from obstruction ( I didn''t automatically think of that), with these numbers. I worry more when things aren''t so balanced = shallow crown + pavilion.


jill, is this a GIA or AGS stone?

 

[Lorelei]

Date: 7/14/2009 7:59:33 AM
Author: Stone-cold11
You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

I am not suffering from any misconception

, remember I have been reading and studying these issues for a very long time, just saying this diamond is very unlikely to show obstruction, I am of a different opinion to you and expressing it. Shallow shallow combos are more likely to show obstruction, as are shallow pavilioned combos, the combo above looking at everything together is in my opinion not likely to show this effect. Also a 33 deg crown angle is not particularly shallow in any case ( especially outside PS). Are you thinking this because the diamond scores slightly below 1 on the HCA out of interest? Also have you ever seen any diamond show obstruction in person SC?

 

[Lorelei]

Date: 7/14/2009 9:19:56 AM
Author: Ellen

Date: 7/14/2009 7:59:33 AM
Author: Stone-cold11
You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

I wouldn''t say she''s saying that. Just that if you can have a crown that''s leaning slightly shallow, but have a pavilion angle that''s not leaning the same way (balancing things out), obstruction most likely won''t be an issue. I would have to agree. I suppose anything is possible with any stone, but I doubt this stone would suffer from obstruction ( I didn''t automatically think of that), with these numbers. I worry more when things aren''t so balanced = shallow crown + pavilion.


jill, is this a GIA or AGS stone?

Thank you Ellen, that is what I meant.

 

[Ellen]

Welcometh!

 

[John P]

Date: 7/14/2009 5:53:05 AM
Author: Stone-cold11
Numbers looks good, slightly on the shallower side, might have some obstruction issue, IS can tell more. More of a brilliant cut than a balance TIC cut.

SC that combo shouldn't have obstruction issues in normal conditions, especially with 80% lowers. Remember the small table adds crown height. In fact it has CH of 14.6%, nearly identical to 57 40.8 34.5, so it has the geometrical distibution of other TICs.

It misses GIA EX and predicted AGS0 in light performance on the cut guides by a tick (depending on the rounding of course) but I've seen plenty 40.8/33.0 combos receive 0 - it's a matter of minors and cut consistency. An ideal-scope or ASET would certainly tell us more.

 

[Lorelei]

Date: 7/14/2009 10:13:32 AM
Author: John Pollard

Date: 7/14/2009 5:53:05 AM
Author: Stone-cold11
Numbers looks good, slightly on the shallower side, might have some obstruction issue, IS can tell more. More of a brilliant cut than a balance TIC cut.

SC that combo shouldn''t have obstruction issues in normal conditions, especially with 80% lowers. Remember the small table adds crown height. In fact it has CH of 14.6%, nearly identical to 57 40.8 34.5, so it has the geometrical distibution of other TICs.

It misses GIA EX and predicted AGS0 in light performance on the cut guides by a tick (depending on the rounding of course) but I''ve seen plenty 40.8/33.0 combos receive 0 - it''s a matter of minors and cut consistency. An ideal-scope or ASET would certainly tell us more.

Thank you for your input Sir!

 

[jill_s]

The stone is GIA. It seemed to me that the crown seemed a bit shallow compared to other "ideal" stones talked about here, so I was wondering what that would mean. So if I understand everyone correctly, the stone *should* be a nice performer even considering the shallow crown, although an idealscope would be able to confirm this. I don''t have an idealscope to share, I''m trying to decide if the numbers are safe enough for me to have the stone called in. What are the chances that this stone would not be a good performer based on the numbers we have?

 

[jill_s]

When you mention "obstruction", what does that mean? Also, what is the difference you typically see if a stone has a shallow crown or a shallow pavilion?

 

[Lorelei]

Date: 7/14/2009 10:20:42 AM
Author: jill_s
The stone is GIA. It seemed to me that the crown seemed a bit shallow compared to other ''ideal'' stones talked about here, so I was wondering what that would mean. So if I understand everyone correctly, the stone *should* be a nice performer even considering the shallow crown, although an idealscope would be able to confirm this. I don''t have an idealscope to share, I''m trying to decide if the numbers are safe enough for me to have the stone called in. What are the chances that this stone would not be a good performer based on the numbers we have?

Yes. The diamond has real potential to be a beautiful stone, of course Idealscope images are always useful in order to see how everything works together, if not available I would think definitely worth having the diamond called in for evaluation.

 

[Lorelei]

Date: 7/14/2009 10:22:29 AM
Author: jill_s
When you mention 'obstruction', what does that mean? Also, what is the difference you typically see if a stone has a shallow crown or a shallow pavilion?

Ok as we have explained here, obstruction is highly unlikely to be an issue with this diamond. But in simple terms, obstruction is where a diamond can visibly darken if worn in a ring and the viewer bends over it to admire or look at it closely. The viewer's head/ body obstructs light to the diamond making it go dark, once the obstruction is removed ( you stop bending over the diamond) these types of diamonds often look bright and sparkly. No need to worry about this with the diamond above. As explained earlier it is usually shallower proportioned diamonds, ones with shallow pavilion angles and what we call shallow shallows with shallow pavilions and crown angles that show obstruction, and if the lowers (lower girdle facets) are short in these cases this can exacerbate the effect. See this video to watch obstruction in action, the film lower right hand side.

http://diamondscope.pricescope.com/

 

[Ellen]

Date: 7/14/2009 10:15:40 AM
Author: Lorelei

Thank you for your input Sir!

Ditto!

 

[John P]

Date: 7/14/2009 10:20:42 AM
Author: jill_s
The stone is GIA. It seemed to me that the crown seemed a bit shallow compared to other ''ideal'' stones talked about here, so I was wondering what that would mean. So if I understand everyone correctly, the stone *should* be a nice performer even considering the shallow crown, although an idealscope would be able to confirm this. I don''t have an idealscope to share, I''m trying to decide if the numbers are safe enough for me to have the stone called in. What are the chances that this stone would not be a good performer based on the numbers we have?

Jill,

It is incorrect to say that this diamond has a shallow crown. The small table allows a comfortable crown height paired with 33.0; which is shallower than Tolkowsky''s 34.5 but still in the near-Tolk area.

In fact, if we want to be literal, GIA does not define a crown angle as even "slightly shallow" until it''s at or near 31.5 degrees. Moderately shallow is at or near 26.5 and "shallow" is at or near 22.0 degrees (on our island of Pricescope we compress real-world envelopes).

You can see, below, that there''s a "give and take" with configurations. Neither of these diamonds has a "shallow crown." Just as CA and PA can balance each other the CA and table size work together here. There will be some slightly different optics with a 40.8/33.0 combo than a 40.8/34.5, but they''re brought closer together by the smaller table.

- Usual disclaimer about "perfect" wire frame simulations, not intended to represent the actual diamond (below).

 

[John P]

Date: 7/14/2009 10:38:09 AM
Author: Ellen

Date: 7/14/2009 10:15:40 AM
Author: Lorelei

Thank you for your input Sir!

Ditto!

Sure thing. Cheers to everyone.

 

[strmrdr]

Date: 7/14/2009 7:59:33 AM
Author: Stone-cold11
You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

Not exactly....

there are certain pavilion angles that will never have "significant" obstruction issues <-- is true

certain angles that will definitely have them regardless of crown angles <-- also true within the range of common crown angles.
For example a 40 degree pavilion would need a 39.5 degree crown with a 57% table to balance it. Which you arent going to see cut these days in an RB.

If you want to discuss this further start a new thread.

 

[jill_s]

Date: 7/14/2009 11:33:06 AM
Author: John Pollard

Date: 7/14/2009 10:20:42 AM

Author: jill_s

The stone is GIA. It seemed to me that the crown seemed a bit shallow compared to other ''ideal'' stones talked about here, so I was wondering what that would mean. So if I understand everyone correctly, the stone *should* be a nice performer even considering the shallow crown, although an idealscope would be able to confirm this. I don''t have an idealscope to share, I''m trying to decide if the numbers are safe enough for me to have the stone called in. What are the chances that this stone would not be a good performer based on the numbers we have?

Jill,


It is incorrect to say that this diamond has a shallow crown. The small table allows a comfortable crown height paired with 33.0; which is shallower than Tolkowsky''s 34.5 but still in the near-Tolk area.


In fact, if we want to be literal, GIA does not define a crown angle as even ''slightly shallow'' until it''s at or near 31.5 degrees. Moderately shallow is at or near 26.5 and ''shallow'' is at or near 22.0 degrees (on our island of Pricescope we compress real-world envelopes).


You can see, below, that there''s a ''give and take'' with configurations. Neither of these diamonds has a ''shallow crown.'' Just as CA and PA can balance each other the CA and table size work together here. There will be some slightly different optics with a 40.8/33.0 combo than a 40.8/34.5, but they''re brought closer together by the smaller table.


- Usual disclaimer about ''perfect'' wire frame simulations, not intended to represent the actual diamond (below).

John,

Thank you so much! This was really helpful. I''m still not sure I totally get how all these different angles work together, but I''m trying to figure it out. I''m still amazed that diamond shopping is a stone by stone thing and there are so many factors to consider when making a purchase.

 

[Lula]

Thanks, John, a good reminder that we need to look at crown and pavilion % and lower girdle facet %, too, to determine the quality of the cut.

I continue to learn from PS -- right now my latest obsession is how table size works with the other angles/percentages!

 

[Lorelei]

Date: 7/14/2009 11:33:06 AM
Author: John Pollard

Date: 7/14/2009 10:20:42 AM
Author: jill_s
The stone is GIA. It seemed to me that the crown seemed a bit shallow compared to other 'ideal' stones talked about here, so I was wondering what that would mean. So if I understand everyone correctly, the stone *should* be a nice performer even considering the shallow crown, although an idealscope would be able to confirm this. I don't have an idealscope to share, I'm trying to decide if the numbers are safe enough for me to have the stone called in. What are the chances that this stone would not be a good performer based on the numbers we have?

Jill,

It is incorrect to say that this diamond has a shallow crown. The small table allows a comfortable crown height paired with 33.0; which is shallower than Tolkowsky's 34.5 but still in the near-Tolk area.

In fact, if we want to be literal, GIA does not define a crown angle as even 'slightly shallow' until it's at or near 31.5 degrees. Moderately shallow is at or near 26.5 and 'shallow' is at or near 22.0 degrees (on our island of Pricescope we compress real-world envelopes).

You can see, below, that there's a 'give and take' with configurations. Neither of these diamonds has a 'shallow crown.' Just as CA and PA can balance each other the CA and table size work together here. There will be some slightly different optics with a 40.8/33.0 combo than a 40.8/34.5, but they're brought closer together by the smaller table.

- Usual disclaimer about 'perfect' wire frame simulations, not intended to represent the actual diamond (below).

Excellent info as usual John, thank you! And as noted earlier a very good reminder that a 33 CA is not actually shallow ( especially in the non PS world).

Jill you will do fine, you have had an expert's input to reassure you that as I said earlier this diamond will not suffer from obstruction and that it is definitely worthy of further evaluation. Let us know how you get on!

 

[stone-cold11]

Date: 7/14/2009 10:13:32 AM
Author: John Pollard

Date: 7/14/2009 5:53:05 AM
Author: Stone-cold11
Numbers looks good, slightly on the shallower side, might have some obstruction issue, IS can tell more. More of a brilliant cut than a balance TIC cut.

SC that combo shouldn''t have obstruction issues in normal conditions, especially with 80% lowers. Remember the small table adds crown height. In fact it has CH of 14.6%, nearly identical to 57 40.8 34.5, so it has the geometrical distibution of other TICs.

It misses GIA EX and predicted AGS0 in light performance on the cut guides by a tick (depending on the rounding of course) but I''ve seen plenty 40.8/33.0 combos receive 0 - it''s a matter of minors and cut consistency. An ideal-scope or ASET would certainly tell us more.

John, I never say the crown is shallow, I mean the pavilion angle complimenting the crown is on the shallower side.

I would have thought a smaller LF number would help more in this case? Sure the arrows will be thicker but the space between the arrows are less likely to go dark with shadow?

 

[Lorelei]

Date: 7/14/2009 5:06:17 PM
Author: Stone-cold11

Date: 7/14/2009 10:13:32 AM
Author: John Pollard

Date: 7/14/2009 5:53:05 AM
Author: Stone-cold11
Numbers looks good, slightly on the shallower side, might have some obstruction issue, IS can tell more. More of a brilliant cut than a balance TIC cut.

SC that combo shouldn't have obstruction issues in normal conditions, especially with 80% lowers. Remember the small table adds crown height. In fact it has CH of 14.6%, nearly identical to 57 40.8 34.5, so it has the geometrical distibution of other TICs.

It misses GIA EX and predicted AGS0 in light performance on the cut guides by a tick (depending on the rounding of course) but I've seen plenty 40.8/33.0 combos receive 0 - it's a matter of minors and cut consistency. An ideal-scope or ASET would certainly tell us more.

John, I never say the crown is shallow, I mean the pavilion angle complimenting the crown is on the shallower side.

I would have thought a smaller LF number would help more in this case? Sure the arrows will be thicker but the space between the arrows are less likely to go dark with shadow?

SC, I would like to know why you thought this diamond would show obstruction? Also looking at the angle configuration on this diamond one would assume you meant the crown angle was shallow as the pavilion angle is not shallow at all. Also you normally point out what angles you think are too shallow or steep, for example you would have said something like that pavilion angle is too shallow for that crown angle, that is normally how you describe it.

 

[stone-cold11]

Date: 7/14/2009 11:49:50 AM
Author: strmrdr

Date: 7/14/2009 7:59:33 AM

Author: Stone-cold11

You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

Not exactly....

there are certain pavilion angles that will never have 'significant' obstruction issues <-- is true

certain angles that will definitely have them regardless of crown angles <-- also true within the range of common crown angles.

For example a 40 degree pavilion would need a 39.5 degree crown with a 57% table to balance it. Which you arent going to see cut these days in an RB.

If you want to discuss this further start a new thread.

I am not saying extreme pav angles which you are implying here. It was made in the past thread which I will not bother to look.

More of the range, greater than 40.8 for case 1 and smaller than 40.6 for case 2. Anyway, I will bookmark this page and refer it again if/when the above cases are make again.

 

[Lorelei]

Date: 7/14/2009 5:12:40 PM
Author: Stone-cold11

Date: 7/14/2009 11:49:50 AM
Author: strmrdr

Date: 7/14/2009 7:59:33 AM

Author: Stone-cold11

You seems to be under the misconceptions that there are certain pavilion angles that will never have obstruction issues and certain angles that will definitely have them regardless of crown angles.

Not exactly....

there are certain pavilion angles that will never have 'significant' obstruction issues
certain angles that will definitely have them regardless of crown angles
For example a 40 degree pavilion would need a 39.5 degree crown with a 57% table to balance it. Which you arent going to see cut these days in an RB.

If you want to discuss this further start a new thread.

I am not saying extreme pav angles which you are implying here. It was made in the past thread which I will not bother to look.

More of the range, greater than 40.8 for case 1 and smaller than 40.6 for case 2. Anyway, I will bookmark this page and refer it again if/when the above cases are make again.

Are you addressing me?

 

[stone-cold11]

Date: 7/14/2009 5:09:32 PM
Author: Lorelei
SC, I would like to know why you thought this diamond would show obstruction? Also looking at the angle configuration on this diamond one would assume you meant the crown angle was shallow as the pavilion angle is not shallow at all. Also you normally point out what angles you think are too shallow or steep, for example you would have said something like that pavilion angle is too shallow for that crown angle, that is normally how you describe it.

To me, it is always about complimenting angles and table. You will note that I usually say a pav angle is too shallow or too deep for a crown angle. Never the other way around. I guess I miss that here.

You always try and correct me by saying the pav angle is not too deep/shallow, but that is not taking into account of the crown angles. 41 PA is just fine for a 33.5 CA for 55-57% T but definitely not for a 35 CA with the same T range.

 

[Lorelei]

Date: 7/14/2009 5:19:15 PM
Author: Stone-cold11

Date: 7/14/2009 5:09:32 PM
Author: Lorelei
SC, I would like to know why you thought this diamond would show obstruction? Also looking at the angle configuration on this diamond one would assume you meant the crown angle was shallow as the pavilion angle is not shallow at all. Also you normally point out what angles you think are too shallow or steep, for example you would have said something like that pavilion angle is too shallow for that crown angle, that is normally how you describe it.

To me, it is always about complimenting angles and table. You will note that I usually say a pav angle is too shallow or too deep for a crown angle. Never the other way around. I guess I miss that here.

You always try and correct me by saying the pav angle is not too deep/shallow, but that is not taking into account of the crown angles. 41 PA is just fine for a 33.5 CA for 55-57% T but definitely not for a 35 CA with the same T range.

I always take into account the WHOLE picture when judging any diamond, also there is a lot more flexibility with crown angles than pavilion. Yes it is a question of balance, but in some cases if you are swinging too far at opposite extremes, a steep pavilion angle even balanced with a shallow crown angle can lead to various undesirable issues such as leakage and colour entrapment.

Yes a 41 pavilion angle should be fine with a 33.5 CA, as we know 35/41 is hitting the steep deep zone, steep deep being a term in use on PS for a long time now. With the 40.8 pavilion angle I thought you would know that it is a good angle which is a balance for a crown angle in either a shallower or slightly steeper direction.

Also I am very interested to know why you thought the diamond in question could show obstruction?