Are there any photos documenting the negative aspects of a "Steep Deep"

[Lorelei]

Date: 11/12/2009 7:37:49 PM
Author: FB.
As Rockdiamond says; show facts, not opinions - and keep the personal attacks out of it.

While I appreciate that there a risks in buying a steep/deep 'triple excellent', I would like to see pictures showing some that are as bad as people make them out to be.
So far, the pictures have mostly shown non-Excellent-cut stones as examples of steep/deep.

Pricescopers are very fond of insisting that stone's can't be judged by numbers, so why should people believe that just because the stone has 36.0/41.4, it will be a bad performer. Going by the usual PS logic, even 'steep/deep' stones should have an IS/ASET requested because *apparently* numbers count for nothing.

A hearty ditto to that.

FB, experience has taught me ( and the following are my opinions) anyway that in many cases 36/41.4 is going to show leakage and sometimes a 41.4 PA will show leakage anyway along with other issues such as colour entrapment and so on. An image is useful in order to judge the extent of the leakage as sometimes longer lower girdle facets and tight cutting precision can help to minimize light loss. With a 36/41.4 angle combo on paper I would be very cautious however and would be doubtful that the leakage would be slight, with a near colourless diamond of this angle configuration that would also influence my thinking, as take for example an I or J colour, colour entrapment would be a possibility with this angle combo. But as noted earlier overall cutting precision and LGF length etc can sometimes help these stones.

 

[Rockdiamond]

Lorelei, and FB- thank you so much for pointing out that personal attacks add nothihng positive to this, or any conversation.
It''s important to remember- for all of us- that if someone attacks others, they are speaking more about themselves.

I am continuing as there does seem to be many people interested in this topic, and seeing photos showing this effect.


I do feel that photos can provide meaningful info abut the cut of a diamond.
Not enough to grade the diamond, but enough to show us true negative effects of a stone''s cut.
The photo I posted clearly shows what I consider to be a dark area in the middle of the table, caused by what''s referred to here as "Leakage"

Lorelei- in reading your post it occured to me a basic difference in how we look at diamonds.
You ( and others) have taken a lot of time to study angles, and how they correlate to actual appearances.
I am more of a hands on guy- looking at actual diamonds to grade them.
Using angles seems like "reverse engineering" to me.
But clearly, many folks with good intentions use these to advise others.
A lot of folks get benefit from it here.
I would again stress that I am not saying it''s wrong to use either method. Neither method will be preferred by all interested parties.

When we speak of leakage- if there''s significant leakage, and that leakage was a problem, wouldn''t that show in a photo?


Also an intersting point about color entrapment.
Would you think photos could depict this?

Again- just for the sake of conversation, not to insult anyone: Is it possible that minor leakage is not even noticable- or might even add to a look some people prefer?

 

[FB.]

In coloured stones, some leakage is good because it enhances the colour, due to less intense light return.

The oppotite reason is why people are happy to go with quite low colour diamonds when they have excellent light return - because the white light reflection overwhelms the trace of body colour.

Perhaps we should consider steep/deep to be more problematic in the more tinted stones, where, as Lorelei says; their will be colour entrapment. That would imply that less tinted steep/deep stones (perhaps D-F?) would not be quite such a negative as G-J or lower. Of course "negative" assumes that you like your diamonds to face up whiter.

For those who like their colours warmer, maybe a steep/deep will slightly increase the warmth, although in so doing, you make the stone look a lower colour grade than it actually is.

 

[Rockdiamond]

Date: 11/13/2009 2:47:20 PM
Author: FB.
In coloured stones, some leakage is good because it enhances the colour, due to less intense light return.

We agree on this one FB- but the photo I posted is "over the top"- too much leakage and too concentrated on one spot IMO

The oppotite reason is why people are happy to go with quite low colour diamonds when they have excellent light return - because the white light reflection overwhelms the trace of body colour.

Perhaps we should consider steep/deep to be more problematic in the more tinted stones, where, as Lorelei says; their will be colour entrapment. That would imply that less tinted steep/deep stones (perhaps D-F?) would not be quite such a negative as G-J or lower. Of course ''negative'' assumes that you like your diamonds to face up whiter.

For those who like their colours warmer, maybe a steep/deep will slightly increase the warmth, although in so doing, you make the stone look a lower colour grade than it actually is.

Again PHOTOS!!!!
If the effects are noticeable, we should be able to see them in photos.

 

[Garry H (Cut Nut)]

Date: 11/13/2009 2:47:20 PM
Author: FB.
In coloured stones, some leakage is good because it enhances the colour, due to less intense light return.


The oppotite reason is why people are happy to go with quite low colour diamonds when they have excellent light return - because the white light reflection overwhelms the trace of body colour.


Perhaps we should consider steep/deep to be more problematic in the more tinted stones, where, as Lorelei says; their will be colour entrapment. That would imply that less tinted steep/deep stones (perhaps D-F?) would not be quite such a negative as G-J or lower. Of course ''negative'' assumes that you like your diamonds to face up whiter.


For those who like their colours warmer, maybe a steep/deep will slightly increase the warmth, although in so doing, you make the stone look a lower colour grade than it actually is.

FB - One important feature in making lighter fancy colored rough look good is increasing the average ray path lengths throught the stone.
In the case of simple direct leakage the leaked light does nothing to increase the ray path length - the exact opposite is true.

David - I am not sure if you are saying the leakage in the stone pic you posted is positive or negative for the stones appearance?

 

[FB.]

Today I was comparing two pear shaped diamonds of similar size and length:width ratios - in a variety of light conditions.
The proportions were approximately as follows:

#1
Table: 55%
Crown height: 14.8%
Girdle: thin to thick
Pavilion depth: 44.8%
Total depth: 62.3%

#2
Table: 57%
Crown height: 15.7%
Girdle: thin to sl.thick
Pavilion depth: 43.8%
Total depth: 64.1%


So, you might think that #2 is approaching the pear equivalent of a steep deep and is the inferior stone.

In fact, the two stones have a different character and it depends on what you're looking for.

Speaking in HCA-type language, I'd rate them:

#1
Light return: Very good
Fire: Good
Scintillation: Excellent
Spread: Very good

#2
Light return: Good
Fire: Excellent
Scintillation: Very good
Spread: Very good

So, bearing in mind that fiery stones suit different environments to bright stones, then the best choice might depend on what you plan to wear it for.

Does the same apply to the GIA Ex grades?

 

[Rockdiamond]

Garry- personally I find the leakage pattern in that Brownish Yellow to be unattractive, so I see it as a negative.
This is my taste coming into play- but I think that many interested diamond lovers would not prefer such a dark area in the middle.
One thing I have learned over the years though. Tastes are extremely varied from one person to the next.
There ARE some people who would prefer it that way.
Not me though.

 

[Allison D.]

David, the photos you've posted don't appear relevant to this discussion by your own criteria.

Your argument has been that angles considered by PSers to be 'steep deep' do not negatively impact stones that earn the GIA EX grade. The discussion is about effects that appear on ROUND stones receiving the GIA EX grade.

Earlier in this thread, a poster offered a picture of a round ungraded stone that appeared dark to her, and you said the picture was meaningless because it wasn't illustrating a GIA EX stone with negative effects.

Unless this fancy yellow non-round stone slipped through the cracks to receive a cut grade from GIA, it's not germane to the topic even for illustrative purposes. Unless you're willing to stay on the topic which you yourself picked, I can't imagine how this thread will result in any meaningful progress, so I'll respectfully bow out.

 

[Rockdiamond]

Date: 11/13/2009 4:02:58 PM
Author: Allison D.
David, the photos you''ve posted don''t appear relevant to this discussion by your own criteria.

Your argument has been that angles considered by PSers to be ''steep deep'' do not negatively impact stones that earn the GIA EX grade. The discussion is about effects that appear on ROUND stones receiving the GIA EX grade.

Earlier in this thread, a poster offered a picture of a round ungraded stone that appeared dark to her, and you said the picture was meaningless because it wasn''t illustrating a GIA EX stone with negative effects.

Unless this fancy yellow non-round stone slipped through the cracks to receive a cut grade from GIA, it''s not germane to the topic even for illustrative purposes. Unless you''re willing to stay on the topic which you yourself picked, I can''t imagine how this thread will result in any meaningful progress, so I''ll respectfully bow out.

Hi Allison

All due respect but I request that you not paraphrase what I''m saying. If you would insert the quote, I''d be happy to respond
Jim did post a photo of a stone that clearly showed a very dark center, but it was not a GIA EX cut grade- is that what you''re referring to? I though that photo did add a lot to the conversation.

I posted the photos of the radiant to show that it is possible to see such effects in a photo of a diamond. As such, the photo does demonstrate what I''m referring to.
It clearly shows a dark center.


Let me relate some of the first things we were taught at Harry Winston, about cut.
We were learning on Single Cuts- which actually makes it easier to spot some of the negative effects of depth- one way of the other.
To put it simply: If the diamond was cut too deep, we were taught that it would have a dark center.
If it was cut too shallow, there would be a ring- called a fish eye- around the table.
if it was cut just right there would be a reflection that you''d see halfway down the pavilion- as viewed through the table.

Single cuts are great to use for training purposes because you really get to see the "cause and effect"

The photo I posted above shows what a dark center looks like on a diamond.
Obviously it''s not a steep deep, or round- but the dark area is representative of what a stone that is cut too deep may show.

 

[Allison D.]

With equally due respect, I post and contribute in the way that makes sense for me. Sometimes that''s via quoting and sometimes it isn''t. Sometimes I''m too lazy to go back pages and quote, and in those instances, I feel comfortable paraphrasing and will likely continue.

I can assure you my feelings won''t be hurt if you choose not to reply because you don''t care for my format. I''ve already accepted that your intentions and mine in this thread don''t gel, so I don''t consider this a discussion between you and me. I consider it a general, public conversation so any contribution I''m making at this point is for the benefit of other readers.

 

[Karl_K]

Date: 11/13/2009 5:33:49 PM
Author: Allison D.
With equally due respect, I post and contribute in the way that makes sense for me. Sometimes that's via quoting and sometimes it isn't. Sometimes I'm too lazy to go back pages and quote, and in those instances, I feel comfortable paraphrasing and will likely continue.


I can assure you my feelings won't be hurt if you choose not to reply because you don't care for my format. I've already accepted that your intentions and mine in this thread don't gel, so I don't consider this a discussion between you and me. I consider it a general, public conversation so any contribution I'm making at this point is for the benefit of other readers.

Same here.
I see the issue in the earlier pictures and it bugs me in real diamonds.
I bugged me before I know what it was called and what caused it when I was first looking at diamonds.
David doesn't acknowledge that it can bug people and his opinion is his opinion.

 

[Garry H (Cut Nut)]

Date: 11/13/2009 5:22:12 PM
Author: Rockdiamond

Date: 11/13/2009 4:02:58 PM

Author: Allison D.

David, the photos you''ve posted don''t appear relevant to this discussion by your own criteria.


Your argument has been that angles considered by PSers to be ''steep deep'' do not negatively impact stones that earn the GIA EX grade. The discussion is about effects that appear on ROUND stones receiving the GIA EX grade.


Earlier in this thread, a poster offered a picture of a round ungraded stone that appeared dark to her, and you said the picture was meaningless because it wasn''t illustrating a GIA EX stone with negative effects.


Unless this fancy yellow non-round stone slipped through the cracks to receive a cut grade from GIA, it''s not germane to the topic even for illustrative purposes. Unless you''re willing to stay on the topic which you yourself picked, I can''t imagine how this thread will result in any meaningful progress, so I''ll respectfully bow out.

Hi Allison

All due respect but I request that you not paraphrase what I''m saying. If you would insert the quote, I''d be happy to respond

Jim did post a photo of a stone that clearly showed a very dark center, but it was not a GIA EX cut grade- is that what you''re referring to? I though that photo did add a lot to the conversation.


I posted the photos of the radiant to show that it is possible to see such effects in a photo of a diamond. As such, the photo does demonstrate what I''m referring to.

It clearly shows a dark center.



Let me relate some of the first things we were taught at Harry Winston, about cut.

We were learning on Single Cuts- which actually makes it easier to spot some of the negative effects of depth- one way of the other.

To put it simply: If the diamond was cut too deep, we were taught that it would have a dark center.

If it was cut too shallow, there would be a ring- called a fish eye- around the table.

if it was cut just right there would be a reflection that you''d see halfway down the pavilion- as viewed through the table.


Single cuts are great to use for training purposes because you really get to see the ''cause and effect''


The photo I posted above shows what a dark center looks like on a diamond.

Obviously it''s not a steep deep, or round- but the dark area is representative of what a stone that is cut too deep may show.

David that stone you posted most probably has an area near the pavilion that is too shallow - not too deep. Those facets are probably around 20 degrees.

Also I wonder if you understand what causes the effects you observed in the single cuts? The optimum table reflection is usually considered to be closer to 1/3rd (unless the table is very large). When the table reflection starts getting just over 50% you would not have noticed a dark zone inside the table because you would have light leaking toward you. I doubt any of the other ''experts'' at Harry Winston would have known that, and for that matter the GIA where the commonly held and educational practice was to tell people the darkness when the entire table was dark was caused by leakage. That was just so wrong that it is hilarious.

 

[Rockdiamond]

All good points Garry.
I was looking for a photo showing a dark area in the center of the diamond. That photo demonstrates what a dark area looks like.
I don''t have the diamond to check it''s depth, but you very well could be right about the pavillion depth. It still looks dark in the center.

At Winston, we weren''t taught to use anything but our eyes- although at the time Ronald Winston was spending huge bucks on high tech diamond machines such as the predecessor of the colorimeter. There were many people who worked at Winston in the ''70''s who did not need quotes around their status as ''expert''.

I always believed that the darkness in deep single cuts was caused by the steeper angle causing the light to reflect downward towards the floor.
It seemed to me that the fish eye is caused when a stone is too shallow was caused by a reflection into the table of the girdle.
But I have no doubt you are correct about the technical causes.
Knowing how to identify what I saw was important, while the causes seemed less so. After all, I was not going to fix the diamonds on a cutting wheel.
To this day, this is one of the differences in the way I look at diamonds, compared to many here.

The essence of my question remains.
As someone who judges diamonds visually, I''m asking to see what negative aspect of steep deep to look for.

Karl, in response to you post, if I did not make this clear enough: I am not suggesting that people who have identified a characteristic in diamonds they dislike- be it leakage or any other aspect- is wrong to avoid stones based on a charachterisitc they can identify.
No one is wrong if they don''t like leaky diamonds.

But the term itself sounds pejorative to me.
Maybe I''m an overly sensitive guy, but we''re talking about people''s preferences for an item that people have a lot of emotional attachment to.
Some people will very much like certain "leakage" in diamonds - and it might be diamonds they currently own.
I''m not trying to "push" one type over the other- just the opposite.
No one is wrong to love something, or to dislike it.

I did not like the dark area in the table of the stone I posted.
I wouldn''t have liked it if it was caused by too steep a pavilion, or too shallow.,
I just didn''t like it.

But that is my preference. There will be people who would like it, therefore describing it in a derogatory manner may insult some people.
If that matters, which I believe, it does.

 

[Garry H (Cut Nut)]

"I always believed that the darkness in deep single cuts was caused by the steeper angle causing the light to reflect downward towards the floor."

The darkness in the table (nailhead) is caused by the same thing as a bow tie in a marquise.
It is the obstruction of light by the viewer, the camera, the lens. You are looking straight back to your self - there is 100% light return and no leakage.
But in the case of most rounds with 50% depth pavilions there is a lot of leakage around the upper girdle facets which makes the diamond look very very smal because of a lack of light return (= darkness). That darkness will remain until the crown angle is droppped below 25 degrees. The table darkness will remain however.

 

[Garry H (Cut Nut)]

Assignment 8 of
the GIA diamond grading
course, copyright 1993, states
“If the pavilion is very deep,
much of the light is leaking
out. Then the table reflection
and the star facets look almost
black, and the stone is called
a ‘nail head’.”

 

[Rockdiamond]

I again bow to your technical knowledge- I'm sure you know what you are talking about.
But it seems to me that the way diamond grader holds the stone has the diamond under a grading lamp, head behind the lamp- outside it's range basically.
How is the head obstructing anything in this position?

 

[Garry H (Cut Nut)]

David if you ant tell me why after all this time handling diamonds and the wisdom that many people have served up to you on this board, I am afraid there is not much point.
Let us know when you conduct your human testing.

 

[Rockdiamond]

As much as I do enjoy posting here, most of my time is spent dealing with cutters, jewelers, clients, staff, etc.
I spend a fair amount of time with other dealers here in New York City as well.
The term "head obstruction" has never come up in a conversation about diamonds. Not once.

I''m honestly looking for a better understanding Garry.
Before I started this thread, I did a search on "Steep Deep"
I looked for photos showing this effect.
I honestly did not find any examples that were dramatically bad. I believe in this thread someone found one that did look a bit dark in the center GIA EX cut grade.
For sure GIA makes mistakes too.
But that''s only one that showed identifiable darkness.
Other examples seem to be within the realm of taste for contrast in the context of knowing what a well cut diamond looks like.

I''m sure I can find twenty different threads about head obstruction. In this context, I''d value your input Garry.
Say I''m holding the diamond under a grading lamp, where there is no possibility of my head interfering with the light source, or casting any shadow on the diamond.
If a diamond is too deep, and looks dark in the center, how is my head affecting this?

Maybe if we''re talking about looking in sunlight- or even normal room lighting.
But diamond grading lamps are designed so that the object underneath is directly under the lamp.

 

[Garry H (Cut Nut)]

Learn (as in comprehend) what an ASET and Ideal-scope does then re ask me please David.

 

[ChunkyCushionLover]

Date: 11/13/2009 3:40:13 PM
Author: FB.
Today I was comparing two pear shaped diamonds of similar size and length:width ratios - in a variety of light conditions.
The proportions were approximately as follows:

#1
Table: 55%
Crown height: 14.8%
Girdle: thin to thick
Pavilion depth: 44.8%
Total depth: 62.3%

#2
Table: 57%
Crown height: 15.7%
Girdle: thin to sl.thick
Pavilion depth: 43.8%
Total depth: 64.1%


So, you might think that #2 is approaching the pear equivalent of a steep deep and is the inferior stone.

In fact, the two stones have a different character and it depends on what you're looking for.

Speaking in HCA-type language, I'd rate them:

#1
Light return: Very good
Fire: Good
Scintillation: Excellent
Spread: Very good

#2
Light return: Good
Fire: Excellent
Scintillation: Very good
Spread: Very good

So, bearing in mind that fiery stones suit different environments to bright stones, then the best choice might depend on what you plan to wear it for.

Does the same apply to the GIA Ex grades?

FB,


Round Brilliant optics have been optimized significantly and even slight leakage under the table can be discerned and avoided.

To date Fancy shapes have not been optimized to the same extent and numerical trends are much weaker thus you don't see anyone here using the term "Steep Deep" in Fancy Shapes. I have never seen that term used in reference to Fancy's because they already have an accepted amount of leakage.

I would also not want to make assumptions on optics based solely on numbers for a pear cut and would want to see an ASET and Idealscope image. I wouldn't even begin to comment on the comparison of two pear shapes especially ones that are likely to fall within the top range of pear cuts.

Although not accepted and with its limitations the AGA old cut class system does show ranges for pear shapes and you will notice how much broader those ranges are than for rounds.
http://www.gemappraisers.com/oldcutgrade.asp

The second pear would get dinged down to Cut 2A due to a deeper crown however that is only one criteria and this stone could still get a 1B grade which is still the second highest cut grade for a pear. Try it out yourself http://www.gemappraisers.com/GradeForm.asp as you left out important information to complete the analysis.

Notwithstanding those cut grading charts I'd still want to see a photgraph, Idealscope(Diam X-ray would be even better) and ASET and better yet a video before I would make any comment on possible darkness in a pear. Your attempt to compare Fancy rules to those of rounds is inappropriate and I hope you see why.

 

[Lorelei]

Date: 11/13/2009 3:40:13 PM
Author: FB.
Today I was comparing two pear shaped diamonds of similar size and length:width ratios - in a variety of light conditions.
The proportions were approximately as follows:

#1
Table: 55%
Crown height: 14.8%
Girdle: thin to thick
Pavilion depth: 44.8%
Total depth: 62.3%

#2
Table: 57%
Crown height: 15.7%
Girdle: thin to sl.thick
Pavilion depth: 43.8%
Total depth: 64.1%


So, you might think that #2 is approaching the pear equivalent of a steep deep and is the inferior stone.

In fact, the two stones have a different character and it depends on what you''re looking for.

Speaking in HCA-type language, I''d rate them:

#1
Light return: Very good
Fire: Good
Scintillation: Excellent
Spread: Very good

#2
Light return: Good
Fire: Excellent
Scintillation: Very good
Spread: Very good

So, bearing in mind that fiery stones suit different environments to bright stones, then the best choice might depend on what you plan to wear it for.

Does the same apply to the GIA Ex grades?

Hiya FB

As a fellow pear lover and owner, I absolutely agree you would really need to see images to judge any pear or the pear themselves, the numbers don''t give enough info and I am not surprised they both have different characteristics.

 

[FB.]

Date: 11/14/2009 5:24:45 AM
Author: Lorelei

Date: 11/13/2009 3:40:13 PM
Author: FB.
Today I was comparing two pear shaped diamonds of similar size and length:width ratios - in a variety of light conditions.
The proportions were approximately as follows:

#1
Table: 55%
Crown height: 14.8%
Girdle: thin to thick
Pavilion depth: 44.8%
Total depth: 62.3%

#2
Table: 57%
Crown height: 15.7%
Girdle: thin to sl.thick
Pavilion depth: 43.8%
Total depth: 64.1%


So, you might think that #2 is approaching the pear equivalent of a steep deep and is the inferior stone.

In fact, the two stones have a different character and it depends on what you're looking for.

Speaking in HCA-type language, I'd rate them:

#1
Light return: Very good
Fire: Good
Scintillation: Excellent
Spread: Very good

#2
Light return: Good
Fire: Excellent
Scintillation: Very good
Spread: Very good

So, bearing in mind that fiery stones suit different environments to bright stones, then the best choice might depend on what you plan to wear it for.

Does the same apply to the GIA Ex grades?

Hiya FB

As a fellow pear lover and owner, I absolutely agree you would really need to see images to judge any pear or the pear themselves, the numbers don't give enough info and I am not surprised they both have different characteristics.

I've been studying pear cuts in great detail in recent times - measuring their proportions and correlating to performance.
I generally consider Mr. Atlas' cut grade estimator to be pretty good at identifying good performers - and unlike HCA, it will also estimate non-round stones quite well:
http://gemappraisers.com/oldcutgrade.asp

Although many PS members don't like number-screening, I have become quite good at predicting performance of non-rounds - I've been pushed in that direction because we are poorly served in the UK.
Being a number-crunching investor-type of person, I have been working on my own modification of AGA and HCA, to suit pears and many other non-rounds - the same general rules that apply to rounds also apply to pears, so, for example; a fiery pear has a larger crown and a bright pear has a smaller crown.

The two stones above demonstrate that point, with the larger crowned stone being more fiery.

I've also become quite good at screening stones just from basic information on the certs, which I know really irritates PS members. Many PS-ers would shoot me down if I elaborated, so I'll stay quiet on what I have found are very highly reliable ways to choose a stone based on only partial information, with no images. But I can state that I am now completely happy to buy stones unseen and without images, using my screening parameters - and that includes determining the likelihood of eye clean!
I can sense the PS members blood beginning to boil at those thoughts, so I'll be off now........

 

[Lorelei]

Date: 11/14/2009 6:56:23 AM
Author: FB.


I''ve also become quite good at screening stones just from basic information on the certs, which I know really irritates PS members. Many PS-ers would shoot me down if I elaborated, so I''ll stay quiet on what I have found are very highly reliable ways to choose a stone based on only partial information, with no images. But I can state that I am now completely happy to buy stones unseen and without images, using my screening parameters - and that includes determining the likelihood of eye clean!
I can sense the PS members blood beginning to boil at those thoughts, so I''ll be off now........

 

[FB.]

Date: 11/14/2009 12:52:45 AM
Author: ChunkyCushionLover

Date: 11/13/2009 3:40:13 PM
Author: FB.
Today I was comparing two pear shaped diamonds of similar size and length:width ratios - in a variety of light conditions.
The proportions were approximately as follows:

#1
Table: 55%
Crown height: 14.8%
Girdle: thin to thick
Pavilion depth: 44.8%
Total depth: 62.3%

#2
Table: 57%
Crown height: 15.7%
Girdle: thin to sl.thick
Pavilion depth: 43.8%
Total depth: 64.1%


So, you might think that #2 is approaching the pear equivalent of a steep deep and is the inferior stone.

In fact, the two stones have a different character and it depends on what you''re looking for.

Speaking in HCA-type language, I''d rate them:

#1
Light return: Very good
Fire: Good
Scintillation: Excellent
Spread: Very good

#2
Light return: Good
Fire: Excellent
Scintillation: Very good
Spread: Very good

So, bearing in mind that fiery stones suit different environments to bright stones, then the best choice might depend on what you plan to wear it for.

Does the same apply to the GIA Ex grades?

FB,


Round Brilliant optics have been optimized significantly and even slight leakage under the table can be discerned and avoided.

To date Fancy shapes have not been optimized to the same extent and numerical trends are much weaker thus you don''t see anyone here using the term ''Steep Deep'' in Fancy Shapes. I have never seen that term used in reference to Fancy''s because they already have an accepted amount of leakage.

I would also not want to make assumptions on optics based solely on numbers for a pear cut and would want to see an ASET and Idealscope image. I wouldn''t even begin to comment on the comparison of two pear shapes especially ones that are likely to fall within the top range of pear cuts.

Although not accepted and with its limitations the AGA old cut class system does show ranges for pear shapes and you will notice how much broader those ranges are than for rounds.
http://www.gemappraisers.com/oldcutgrade.asp

The second pear would get dinged down to Cut 2A due to a deeper crown however that is only one criteria and this stone could still get a 1B grade which is still the second highest cut grade for a pear. Try it out yourself http://www.gemappraisers.com/GradeForm.asp as you left out important information to complete the analysis.

Notwithstanding those cut grading charts I''d still want to see a photgraph, Idealscope(Diam X-ray would be even better) and ASET and better yet a video before I would make any comment on possible darkness in a pear. Your attempt to compare Fancy rules to those of rounds is inappropriate and I hope you see why.

I disagree. The laws of physics regarding light behavior don''t change just because the shape changes.
Flat crown and flat pavilion = lots of leakage out the bottom. The stone can''t help but be dull, although may still be attractive.
Large crown and large pavilion = lots of leakage out the sides. Again, the stone may be dull (especially under the table), but may be attractive to some people, like a GIA steep deep.

 

[stone-cold11]

But geometry is different, angles cannot be the same throughout as the measurement and placement of each facet is different. So what is defined as steep angles in round is still a steep angle in fancy cut, but you just can't defined it purely based on the crown height, total depth simply because it is not symm as in a round brilliant. Unless you have the exact measurement of each facets then that is another thing which is not what you are showing here.

 

[FB.]

Date: 11/14/2009 7:12:48 AM
Author: Stone-cold11
But geometry is different, angles cannot be the same throughout as the measurement and placement of each facet is different. So what is defined as steep angles in round is still a steep angle in fancy cut, but you just can't defined it purely based on the crown height, total depth simply because it is not symm as in a round brilliant. Unless you have the exact measurement of each facets then that is another thing which is not what you are showing here.

Absolutely.

But we know the optimum angles for a round brilliant.
Therefore, if the mid-point of the angles of a fancy overlap with the ideal angles in a round brilliant, from my recent studying, you will get good internal reflection, good light return and good overall performance.
After all, we know that ideals will work well within quite a broad range - 14% crown/43% pavilion work well in a round, as does 17% crown/42% pavilion.
Therefore, by pitching the mid-point angles of a fancy in the ideal range for a round (which would basically be equivalent to seeking a steep/deep set of round proportions), the fancies seem to perform very well indeed.
Consider the pears that I list above. The proportions would be considered steep/deep by PS members if we were talking about a round. But a pear elongates as you move towards the ends, which therefore virtually decreases the crown height and pavilion depth % and brings the various angles into the ideal range as you move halfway round the stone towards the ends, while at the ends, the angles start to becomes rather shallow.
But the overall effect seems to be that the average angle sits nicely in the ideal range and the stone perfoms very well.

Additionally, although GIA certs for fancies state "Profile not to actual proportions", from my detailed analysis of GIA certs fo non-rounds, the profiles are printed correctly for the proportions of the smallest axis of the stone. Therefore, you can get an idea of the approximate crown height and pavilion depths without needing a scan.

On the GIA reports for those two pears, I can use a simple 30cm ruler from my desk, to measure the profile pictures, which give the following:

Pear #1
Crown: 5.75mm
Pavilion: 18.0mm
Width: 40.5mm

Crown height est: 5.75/40.5 = 14.2% (actual Sarin= 14.8%)
Pavilion depth est: 18/40.5 = 44.4% (actual Sarin = 44.8%)

Pear #2
Crown: 6.25mm
Pavilion: 17.25mm
Width: 40.5mm

Crown height est: 6.25/40.5 = 15.4% (actual Sarin = 15.7%)
Pavilion depth est: 17.25/40.5 = 42.5% (actual Sarin = 43.8%)

Not exact proportions, but good enough to make some close approximations as to whether the proportions are compatible with a good stone. You could even plug the numbers into AGA's calculator (link here > http://gemappraisers.com/oldcutgrade.asp <), or look for a steep/deep proportion set on HCA.

I also find that stones in "no-man's land" for weight, seem to have few, if any, cutters tricks - presumable because the stone comfortable managed 1ct.

I'm sure that concept is unacceptable for many PS members, but it seems to work extremely well, based on my studies of recent months. I have yet to find a stone that didn't reveal it's general characteristics using such "crude" methods.

...and I'm expecting to get a serious bashing for suggesting this, but I'm known for telling it like I see it.

 

[stone-cold11]

Actually, you are just lucky.

If you look at how small a deviation in depth is require to change the angles and how small a change in angles is required to push it from great performer to steep/deep proportion, it really does no good to do that kind of approximation.

Also, HCA table are generated from viewing and simulating RB, taking into account of the minor facets. If you look at what the pav mains is actually doing, it is in contrast/obstruction range, meaning if those are the main reflecting facets, the stone will have obstruction problem, bow-tie. It is the minor facets that are doing the reflection and how well they are cut and their relations to each other will be more important to the performance.

 

[Allison D.]

I spend a fair amount of time with other dealers here in New York City as well.
The term ''head obstruction'' has never come up in a conversation about diamonds. Not once.

In the days of Aristotle and Ptolemy, learned Greek astrologers all believed that the Earth, not the Sun, was the center of the universe. During those days, it''s likely the suggestion that the sun might actually be the center of the universe probably didn''t ever come up in conversation among the learned astrologers.

In medieval times, wars were waged with swords, long bows and cross bows. Top military strategists in those days likely never engaged in conversations about how gunpowder might create more efficient weaponry.

 

[Karl_K]

Date: 11/14/2009 10:43:06 AM
Author: Allison D.
I spend a fair amount of time with other dealers here in New York City as well.

The term ''head obstruction'' has never come up in a conversation about diamonds. Not once.


In the days of Aristotle and Ptolemy, learned Greek astrologers all believed that the Earth, not the Sun, was the center of the universe. During those days, it''s likely the suggestion that the sun might actually be the center of the universe probably didn''t ever come up in conversation among the learned astrologers.


In medieval times, wars were waged with swords, long bows and cross bows. Top military strategists in those days likely never engaged in conversations about how gunpowder might create more efficient weaponry.

 

[Serg]

Date: 11/14/2009 10:43:06 AM
Author: Allison D.
I spend a fair amount of time with other dealers here in New York City as well.

The term ''head obstruction'' has never come up in a conversation about diamonds. Not once.


In the days of Aristotle and Ptolemy, learned Greek astrologers all believed that the Earth, not the Sun, was the center of the universe. During those days, it''s likely the suggestion that the sun might actually be the center of the universe probably didn''t ever come up in conversation among the learned astrologers.


In medieval times, wars were waged with swords, long bows and cross bows. Top military strategists in those days likely never engaged in conversations about how gunpowder might create more efficient weaponry.

Bruce Harding at least 30+ years ago explained Head obscuration in work "Faceting limits"
http://www.gemology.ru/cut/english/faceting/f1.htm#dead