confusion about shallow diamonds

[Stephan]

A lot of Pricescope members sound the alarm when a consumer asks questions about a diamond with a crown angle lower than 34 degrees.
I think you can go much lower and still have a gorgeous diamond, as long as the pavilion has a 40.8/41 degrees angle.
Of course, with a 40.6 degrees pavilion, you shouldn’t go much lower than a 34 degrees crown.
If I had to make a blind buy, I would prefer a 32/41 over a 34/40.6 because I think it is less risky in matter of obstruction issues.
What do you think?

 

[Upgradable]

Stephan, thanks so much for representing an area that does often get scowled at! Diamonds really can be beautiful in many different combos. I''m so glad there are enough sparklie afficianodes here to give info on many different combos!

 

[Lorelei]

Date: 3/23/2010 8:47:27 AM
Author:QueenMum
A lot of Pricescope members sound the alarm when a consumer asks questions about a diamond with a crown angle lower than 34 degrees.
I think you can go much lower and still have a gorgeous diamond, as long as the pavilion has a 40.8/41 degrees angle.
Of course, with a 40.6 degrees pavilion, you shouldn’t go much lower than a 34 degrees crown.
If I had to make a blind buy, I would prefer a 32/41 over a 34/40.6 because I think it is less risky in matter of obstruction issues.
What do you think?

I agree. There are many proportion configurations that can produce a beautiful diamond.

One thing to add is that a crown angle of 32.5% or below and a very thin girdle needs careful evaluation to make sure there aren't any potential durability issues, in which case ask a trusted expert to inspect the stone.

 

[Karl_K]

I think it depends on the rest of the numbers and images and what is in the averages.

 

[Lula]

Did John Pollard's article (written last year) have photos of different combinations for comparison? I can't remember the name of the article!

But I do remember that the photos were good examples of the visual differences between "bright, white" stones with larger tables, and more splintery flash and stones cut to more Tolk-like proportions with smaller tables and distinct on-off contrast, with broader flash.

Or am I remembering incorrectly?

ETA: Sorry -- posted this in the wrong thread.

 

[Paul-Antwerp]

Stephan,

You are asking a question that makes no sense. Let me try to explain.

First, your point ''I think you can go much lower and still have a gorgeous diamond, as long as the pavilion has a 40.8/41 degrees angle.'' cannot be denied. In a sense, yes, you can.

But jumping from that theoretical possibility to ''If I had to make a blind buy, I would prefer a 32/41 over a 34/40.6'' is a giant leap in your reasoning.

The general advice here on PS is to use the HCA as a rejection-tool. If the stone passes, a consumer should check out the following steps, being for a round generally a good picture of the ideal-scope. Let us assume that we have already passed the rejection-test of the lab-grade. I would advice against basing your decision on the HCA or the average proportions only. What you call a ''blind buy'' is actually a gamble.

After a round brilliant has passed the three rejection-tests of the lab''s cut-grade, the HCA and the ideal-scope, a consumer can go towards the phase of visual observation and selection. And both 32/41 and 34/40.6 can probably pass these rejection-tests. But since these tests all judge brightness mainly, one should assess fire and scintillation in-real-life. Not taking this into account, a consumer is still gambling, a much smaller gamble, but still.

As for your remark about the risk of obstruction issues, we should add that your vision and assessment is slightly different, since you see with only one eye. As such, you will most likely see certain obstruction issues that most people will not observe.

All in all, I would like to advice that we try to avoid simplifying a diamond''s assessment to its average angles only.

Live long,

 

[oldminer]

Diamonds with total depth percentages which are "shallow" will have a larger visual surface area for their weight. At some point, shallowness will decrease light return and the stone gradually becomes less brilliant. So long as certain related combinations of crown angle and pavilion angles are present the shallowness has little to no effect on brightness. Once the diamond diverges from these properly related angles of crown to pavilion, then something will start to be come visiblly different in the light return character of the diamond. You may like the way it looks even when it does not have maximized light return, but the stone will decline in the standard "ideal" rating systems.

The I-S, HCA and ASET can screen for proper performance of light while handling crown and pavilion angle variations. If you choose to go away from the norm, you must physically look at the diamond before you will be sure it works for you.

 

[Stephan]

Date: 3/23/2010 9:55:50 AM
Author: Paul-Antwerp
Stephan,

You are asking a question that makes no sense. Let me try to explain.

First, your point ''I think you can go much lower and still have a gorgeous diamond, as long as the pavilion has a 40.8/41 degrees angle.'' cannot be denied. In a sense, yes, you can.

But jumping from that theoretical possibility to ''If I had to make a blind buy, I would prefer a 32/41 over a 34/40.6'' is a giant leap in your reasoning.

The general advice here on PS is to use the HCA as a rejection-tool. If the stone passes, a consumer should check out the following steps, being for a round generally a good picture of the ideal-scope. Let us assume that we have already passed the rejection-test of the lab-grade. I would advice against basing your decision on the HCA or the average proportions only. What you call a ''blind buy'' is actually a gamble.

After a round brilliant has passed the three rejection-tests of the lab''s cut-grade, the HCA and the ideal-scope, a consumer can go towards the phase of visual observation and selection. And both 32/41 and 34/40.6 can probably pass these rejection-tests. But since these tests all judge brightness mainly, one should assess fire and scintillation in-real-life. Not taking this into account, a consumer is still gambling, a much smaller gamble, but still.

As for your remark about the risk of obstruction issues, we should add that your vision and assessment is slightly different, since you see with only one eye. As such, you will most likely see certain obstruction issues that most people will not observe.

All in all, I would like to advice that we try to avoid simplifying a diamond''s assessment to its average angles only.

Live long,

Hi Paul,
If I understand you correctly, than I totally agree with you:
The best way to judge a diamond, if it passes all the tests (certification, HCA, IS), is to view it in real life.
That’s precisely my point: a lot of pricescopers think 32.0/33.5 crowns are ugly or that they have less fire, without having seen them in real life!

 

[Stephan]

Date: 3/23/2010 10:54:26 AM
Author: oldminer
Diamonds with total depth percentages which are ''shallow'' will have a larger visual surface area for their weight. At some point, shallowness will decrease light return and the stone gradually becomes less brilliant. So long as certain related combinations of crown angle and pavilion angles are present the shallowness has little to no effect on brightness. Once the diamond diverges from these properly related angles of crown to pavilion, then something will start to be come visiblly different in the light return character of the diamond. You may like the way it looks even when it does not have maximized light return, but the stone will decline in the standard ''ideal'' rating systems.

The I-S, HCA and ASET can screen for proper performance of light while handling crown and pavilion angle variations. If you choose to go away from the norm, you must physically look at the diamond before you will be sure it works for you.

Great post David!
If you choose to go away from the norm...
Is 32/41 away from the norm if the idealscope picture is nice?
A lot of pricescopers hesitate to buy such diamonds, even if the IS picture is nice, and that is what I''m fighting against.

 

[Stephan]

Date: 3/23/2010 9:55:50 AM
Author: Paul-Antwerp

As for your remark about the risk of obstruction issues, we should add that your vision and assessment is slightly different, since you see with only one eye. As such, you will most likely see certain obstruction issues that most people will not observe.

That''s true!
Then everything that looks good to my unique eye will look good to a camera.
Like me, the camera doesn''t have a second eye to compensate leakage or obstruction.

 

[kenny]

I have seen pics of diagrams of light rays moving through a side view of a diamond.

Wouldn't it be cool if there was a moving animation graphic of this?
You could enter those four numbers we enter into the HCA and watch light enter, reflect, and leave the diamond.

We could change one number and watch the effect as light rays stop exiting the crown and leak out the bottom of the diamond.
It would also be cool if you didn't have to download (pay for) software to do this.

Does this exist?
Is it even possible?

 

[kenny]

The tool would look something like this but there would be only one image.
The light rays would change direction as you change a proportion.

 

[Stephan]

Hi Kenny!
For such an application, minor facet information is as important as crown/pavilion information.
Did you buy DiamCalc?

 

[Stephan]

Date: 3/23/2010 12:20:12 PM
Author: kenny
The tool would look something like this but there would be only one image.
The light rays would change direction as you change a proportion.

The old Gemcad for DOS already was able to do that.
I think you can find it for free.

 

[kenny]

Do those programs work on a mac?

I was hoping for a simple tool like HCA that you don't have to download.

I think people are a zillion times more likely to use HCA than download software, especially since HCA is simple and free.

I was hoping for a tool for everyone, not just geeks (no insult intended)

 

[Stephan]

DiamCalc could work on a MAC, but I may be wrong.
You can contact them or David Atlas who sells the program.

 

[oldminer]

Kenny; The problem with the four images of light travel you posted is what happens when the crown angle goes lower and the pavilion angle relatively grows higher. Light performance may not be degraded. There are many interrealted possible scenarios. Whe the total depth changes that is very different than when the total depth remains relatively constant and only the two angles chage in proper relation to one another.

32/41 would not be anything I would call "scary" or "bad". The other parameters that go along with such a diamond may or may not allow the diamond to look its best, but those two numbers alone do not begin to tell the entire story of a diamond.

 

[kenny]

So no tool exists for free?

Notice how often HCA is used here.
Notice how often HCA does not end the diamond cut decision.

Such an animated tool would quickly become indispensable as a rejection tool.
Threads such as this one, exploring the fine points of cut angles that HCA can not answer, would vanish.

How proportions affect light return would be made plain, simple and obvious to the least educated of us.
A picture is worth a thousand words.

 

[Paul-Antwerp]

Stephan,

You did not understand me correctly.

I did not say that it is the best way to judge a diamond, if it passes all the tests (certification, HCA, IS), to view it in real life.
I said that it is the next necessary step to verify what one expects in brightness, and to assess for the first time fire and scintillation.

In your ''fight'' for shallow crowns, you are neglecting the difference between what is theoretically possible and what is most of the times.

Each rejection-tool increases the probability of the stone being great. But even after all the rejection-tools, this does not bring you to 100% certainty, far from it.

In the same way, a shallower crown can be great in theory, but the probability of such a random stone being great is not that high.

Live long,

 

[Paul-Antwerp]

Date: 3/23/2010 12:20:12 PM
Author: kenny
The tool would look something like this but there would be only one image.
The light rays would change direction as you change a proportion.

Kenny,

The graphics posted by you are incorrect, even though many in the industry are using them to explain some basics.

As such, the graphic tool that you are asking for is not relevant to a diamond''s performance, and we definitely cannot reduce its assessment to such a representation.

Live long,

 

[WinkHPD]

Date: 3/23/2010 12:40:06 PM
Author: kenny
So no tool exists for free?

Notice how often HCA is used here.
Notice how often HCA does not end the diamond cut decision.

Such an animated tool would quickly become indispensable as a rejection tool.
Threads such as this one, exploring the fine points of cut angles that HCA can not answer, would vanish.

How proportions affect light return would be made plain, simple and obvious to the least educated of us.
A picture is worth a thousand words.

The problem is that what you are essentially asking for is light tracing ability. The licenses to use this software are very expensive, so it is not possible right now to offer a free version. I remember talking with Jim Caudill at AGS some years ago about why they charged so much for the annual license to use their cut grading software. He said it was to help pay the huge licensing fee that they paid at that time to use the light tracing technology which was copywrited.

What you are wanting is not a simple change the angle, change the diagram, it is very complex and at least last I knew, very expensive. Things may have changed on the technology front, but I doubt you will see what you want for free any time soon.

Wink

 

[Stephan]

Date: 3/23/2010 12:40:39 PM
Author: Paul-Antwerp

In the same way, a shallower crown can be great in theory, but the probability of such a random stone being great is not that high.

So should I just forget about it because such diamonds are more difficult to find than 62% depth diamonds?

Does a 35/40.8 diamond have a higher probability to look great than a 33.5/40.8?
If yes, please explain.
Thank you!

 

[Paul-Antwerp]

Is your aim to find such a diamond for yourself? Then, nobody should tell you to forget it. It is your decision to search for it and to select the vendor who can assist in the pre-selection in the best possible way, so that you limit the number of unnecessary shipments of diamonds that you eventually will not buy.

Is your aim however to assist unprepared consumers? Then, your ''fight'' for the rights of the unexpected great shallow crown is probably not good advice for that consumer.

Live long,

 

[kenny]

Thanks guys for addressing my idea.

 

[Rockdiamond]

Interesting conversation.
Stephan, I applaud your efforts to examine how the selection, or rejection process seems to work.

The diagrams in Kenny''s post are integral to my views on this.
I agree with Paul that these simplistic diagrams are commonly used by jewelers to explain basics.

In many ways it''s like drawing a stick figure of a man to describe what a person looks like.
Notice how the arrows representing the light are singular- and emanating from only one direction.

In reality a diamond is viewed with light coming from many different directions.
The diagram also has the diamond completely immobile.
In reality a diamond being viewed is constantly moving.

To me, much of the effort calculating light return is just as simplistic in many ways. If a diamond reacts a certain way to certain tests, are those conclusive?
Or do they only show one aspect?

Is there "a norm"?
You never mentioned any particular shape, although I believe your original questions was referring to round diamonds.

If it''s fancy shaped diamonds there is no such thing as "norm".
Even if we are only considering rounds, if we use GIA or AGSL cut grading, there''s quite a bit of variation existing within the top grades....to much to have something called "the norm"

Sara- I wrote a thread discussing the differences between larger table versus smaller table- one of the photos is below.

 

[Stephan]

Date: 3/23/2010 1:15:53 PM
Author: Paul-Antwerp
Is your aim to find such a diamond for yourself? Then, nobody should tell you to forget it. It is your decision to search for it and to select the vendor who can assist in the pre-selection in the best possible way, so that you limit the number of unnecessary shipments of diamonds that you eventually will not buy.

Is your aim however to assist unprepared consumers? Then, your ''fight'' for the rights of the unexpected great shallow crown is probably not good advice for that consumer.

Perhaps... So does a 35/40.8 diamond have a higher probability to look great than a 33.5/40.8? I know I''m boring but that was my unanswered question above.

 

[ChunkyCushionLover]

Date: 3/23/2010 9:48:41 AM
Author: sarap333
Did John Pollard''s article (written last year) have photos of different combinations for comparison? I can''t remember the name of the article!

But I do remember that the photos were good examples of the visual differences between ''bright, white'' stones with larger tables, and more splintery flash and stones cut to more Tolk-like proportions with smaller tables and distinct on-off contrast, with broader flash.

Or am I remembering incorrectly?

ETA: Sorry -- posted this in the wrong thread.

Example 4 in this article is a 33.5/40.8
http://journal.pricescope.com/Articles/72/1/Laboratory-Cut-Grades-What-the-report-doesn%e2%80%99t-show.aspx

Pretty good looking diamond from the images.

Smaller table, steeper crown, thicker arrows.
Larger table, shallower crown, thinner arrows.

This is assuming the same length lower girdle facets, change those and you can run from arrows as thick as an OEC 85%.
LGF % and how the pavillion is cut has a much greater effect on arrow thickness and dispersion(fire) than small variations in crown angle from near tolk proportions.

--------------------------------------------------------------------

To return to QueenMum''s question I am puzzled by the same thing but I don''t see any current threads where a slightly shallower or steeper near TIC crown is slammed.
" think you can go much lower and still have a gorgeous diamond, as long as the pavilion has a 40.8/41 degrees angle."

But what is much lower and at what LGF length and table size?

Octonus posted some charts for 3% girdle bezel, 55% Star (45% upper girdle) and 80% lower girdle facet length using PGS 1.1.2 for lets say 57% table:
http://www.octonus.com/oct/mss/gia-agspgs.phtml

You could go down to 33.5 crown angle or up to 36 at 40.8 pavillion.
At 41 pavillion down to 33
At 41.2 all the way down to 32.

I don''t have any clearly explained metrics to tell me why any of these combinations wouldn''t be quite similar to each other or why all AGS0 diamonds by the PGS light performance software grading wouldn''t be really nice performers, if all other things were created equally especially if the edge to edge brilliance was checked by the idealscope and it passed i.e you didn''t see obstruction or leakage.

If the difference between BIC and TIC is maybe 5-10% in brightness difference and maybe 5% in Dispersion (these are general and disputed) why would changing things still very near tolk make much of a difference?

 

[Lula]

double post...

 

[Lula]

Date: 3/23/2010 2:04:31 PM
Author: Rockdiamond

Sara- I wrote a thread discussing the differences between larger table versus smaller table- one of the photos is below.

Thanks, David -- appreciate it!

 

[Rockdiamond]

You''re welcome Sara!!

in thew photo above the stone on the left has a shallower crown, and larger table- which has relevance to this discussion
We can see a more defined pattern in the stone on the right- however I prefer the lack of that pattern...


The entire conversation is here