Diamond Cut Angles

[Dancing Fire]

Date: 2/28/2010 2:38:58 PM
Author: Wink

Date: 2/28/2010 1:42:30 PM
Author: FB.
Didn't Tolkowsky's theory use an extremely thin girdle?
I thought that once a medium girdle was added, the table size was optimum at 56%.

Could be wrong though......

Many of us love the fire, and many of us prefer more brilliance. Both are acceptable within the confines of the AGS 0 cut grade, so I am uncomfortable seeing anyone try to say they are not correct without a solid reason why.

Wink

right on Wink!!

i for one would give up a little brilliance for some extra "FIREWORKS"

Wink,i have a Q for ya...why don't Paul cut some RBs with smaller tables?

 

[Paul-Antwerp]

Dancing Fire,

In order to answer your question, I have to give my view on other subjects raised in this thread first. And if I consider the complete picture, this will also affect some more general points, that often are raised, but that I find too much of a generalisation.

So, if you wish, bear with me for a very long post.

Soontomarry, the suggested cut values of niceice.com are interesting, but you need to understand their values and their limitations. Todd Gray of NiceIce (a regular poster here and a friend) uses these values as a first selection of the stones that he might call in for purchase. In fact, I think that his actual selection-values are even somewhat stricter. However, these values are only a first selection (actually rejection) for him, and is followed by analysis on various other tools and his own visual observation, with the latter being the most important.

As an answer to your questions, no, only being within these value-ranges does not guarantee that the stone will have the best cut possible, as is demonstrated by the fact that NiceIce performs a lot of extra analyses and rejections after this initial rejection/selection.

Also, yes, there are most probably other combos outside of these ranges, depending somewhat on personal preference, and the list of NiceIce clearly reflects their personal preference and their search for the ultimate best in their eyes.

The pavilion angle stated by NiceIce as such is not too restrictive, since the correctness of the pavilion angle is the main driver of light return, but again, this choice clearly reflects the very selective criteria of NiceIce.

Stone-Cold, if you say that you can basically dismiss the numbers if IS/ASET is available, I have my doubts. I would definitely suggest using both in tandem as a minimum, especially with the numbers generally coming from an independent source (the grading-lab) and the pictures coming from the vendor. It took us very long to master our picture-taking and I see many vendors still struggling. As such, I find it very hard to read certain IS/ASET''s since I cannot assess the photographic set-up.

As for your call to widen the table-range, this is dependent upon personal taste, and basically covered in my answer to Soontomarry above.

Dreamer and CCL, you are right in your preference for the HCA as a first selection-tool, but I think that Todd''s list of values probably comes to the same or a slightly stricter result in a much faster elimination.

FB and Wink, your discussion about the range being 55-57 or 53-57 is dependent upon personal preference. However, there seems to be an undertone in your posts that a smaller table correlates with the stone exhibiting more fire. While I cannot say with 100% certainty that this assessment is incorrect, I always had serious doubts about it, because it simply does not seem logical to me that one basic parameter dictates fire so much, while we need all the proportions working together to create brightness. Let me explain further.

To me, the assessment that a smaller table/higher crown improves fire is still based upon the old gemological rule that brightness (brilliance) is the enemy of fire. The latter, old rule has been proven to be out-of-date. Brightness and fire can be present in the same stone, and the observation of fire and not brightness depends more upon the lighting environment, and less on the stone.

With the basis of the rule gone, I seriously doubt every assessment based upon ''A smaller table/higher crown creates more fire''. As such, for me, the FIC does not exist either.

In my experience, light return is essential in the performance of a diamond. This, we combine with a very high optical symmetry, in which the shape of the contrast-pattern is actually less important than the crispness of the pattern. The crispness of the contrast-pattern is the basis for scintillation, which depending on the light environment and the observer can be viewed as dynamic brightness or dynamic fire.

Eventually, this leads me to the answer of DF''s question. Based upon the above, we have our own goal-set of proportions, which combined with our level of optical symmetry (and cooked in some very personal, secret Paul-sauce) leads to what we consider the best combo of all sparkle-factors of a diamond. Sure, cutting the same stone with a slightly smaller table probably could yield a diamond that appeals more to some individuals, it will even bring about a slightly higher yield from most rough, but it lessens the predictability/consistency of our brand.

My apologies for the long post. Congratulations to those who read until the end.

Live long,

 

[Regular Guy]

Presuming (or not) as you say, that one things follows from the other....

Date: 3/1/2010 9:35:05 AM
Author: Paul-Antwerp

To me, the assessment that a smaller table/higher crown improves fire is still based upon the old gemological rule that brightness (brilliance) is the enemy of fire. The latter, old rule has been proven to be out-of-date. Brightness and fire can be present in the same stone, and the observation of fire and not brightness depends more upon the lighting environment, and less on the stone.

Where have we seen this...just so we''re all on the same page (as you suggest we should be....)?

 

[ChunkyCushionLover]

Date: 3/1/2010 11:10:49 AM
Author: Regular Guy
Presuming (or not) as you say, that one things follows from the other....

Date: 3/1/2010 9:35:05 AM
Author: Paul-Antwerp

To me, the assessment that a smaller table/higher crown improves fire is still based upon the old gemological rule that brightness (brilliance) is the enemy of fire. The latter, old rule has been proven to be out-of-date. Brightness and fire can be present in the same stone, and the observation of fire and not brightness depends more upon the lighting environment, and less on the stone.

Where have we seen this...just so we''re all on the same page (as you suggest we should be....)?

Yes ditto to this, I want understand this concept better.

 

[Lula]

There are some threads in the PS archives that go into this "fire at the expense of brilliance" and vice-versa argument. I don''t have time now to do an extensive search, but here''s one I found doing a quick search:
2005 thread

 

[whatmeworry]

Paul may be referring to this study by AGSL:

http://www.agslab.com/spie/spie_lo_res.pdf

Here''s the quote(Section 6.2, page 16)

"The fire matrices show that the old diamond-cutting industry

rule of increasing the crown angle to achieve more

fire is not necessarily true. It only significantly applies to

stones at or near the main cutter’s line or about lines passing

by other regions such as the left-bottom and top-right

corners.

Fire results from higher dispersion and this mainly happens

in the stone bezel. Table fire is rare and stones with

significant bezel and table fire are considered superior.

Some stones that exhibit significant fire

27 are designed with

a small table to maximize the bezel area and therefore fire."

 

[Karl_K]

Date: 3/1/2010 11:10:49 AM
Author: Regular Guy
Presuming (or not) as you say, that one things follows from the other....

Date: 3/1/2010 9:35:05 AM

Author: Paul-Antwerp


To me, the assessment that a smaller table/higher crown improves fire is still based upon the old gemological rule that brightness (brilliance) is the enemy of fire. The latter, old rule has been proven to be out-of-date. Brightness and fire can be present in the same stone, and the observation of fire and not brightness depends more upon the lighting environment, and less on the stone.

Where have we seen this...just so we're all on the same page (as you suggest we should be....)?

Watch the cushion vids Garry posted or vids of octavia.
They show it clearly.
With carefully designed virtual facets you can have very high brightness and very high fire.
There is also an advantage to high crowns and secondary light sources and showing brightness and fire. (another huge topic)


The old saying that brilliance is the enemy of fire is true in some cases and very wrong in others.
FIC's work but the understanding of why they work has changed.
What was not understood was the difference that VF size shape and location makes.
It is still little understood by most even by some major labs.
It is the key to diamond performance when combined with complimentary angles to drive them.
Also what was not given proper credit was the difference lighting makes which will always be the largest variable in is it going to show brightness or fire.

 

[Karl_K]

To show you what I am talking about here is a 57% table vs 50% table virtual facet maps with the exact same angles and lowers.
notice the size and shape differences in the virtual facets.
There is no question there will be a difference in performance and sparkle size and shape and number(fire too).

 

[ChunkyCushionLover]

Date: 3/1/2010 2:26:28 PM
Author: Karl_K
To show you what I am talking about here is a 57% table vs 50% table virtual facet maps with the exact same angles and lowers.
notice the size and shape differences in the virtual facets.
There is no question there will be a difference in performance and sparkle size and shape and number(fire too).

But didn't you automatically have to change the crown height to maintain the same crown angle with a different sized table?

 

[Lula]

Thanks, Karl! But, I had the same question as CCL - doesn''t changing the table to that degree require some adjustment in the other angles? If not, then why aren''t all diamonds cut with smaller tables if you get so many more virtual facets? And why were large table stones so common (58, 59, 60...62!), especially in the 1970s and 1980s, when I bought my first diamond? Why the drastic move away from Tolk table proportions in the latter part of the 20th century?

 

[diagem]

Date: 3/1/2010 3:03:17 PM
Author: sarap333
Thanks, Karl! But, I had the same question as CCL - doesn''t changing the table to that degree require some adjustment in the other angles? If not, then why aren''t all diamonds cut with smaller tables if you get so many more virtual facets? And why were large table stones so common (58, 59, 60...62!), especially in the 1970s and 1980s, when I bought my first diamond? Why the drastic move away from Tolk table proportions in the latter part of the 20th century?

Good questions..., not Karl but will try to answer based on my knowledge...

Notice the difference/adjustment in the star facets and the relationship with the upper halves.
Back in the 70''s & 80"s (actually more like 40''s - early 90''s) different rough planing methods were practiced as opposed to 90''s.

 

[Paul-Antwerp]

Date: 3/1/2010 2:58:15 PM
Author: ChunkyCushionLover

Date: 3/1/2010 2:26:28 PM
Author: Karl_K
To show you what I am talking about here is a 57% table vs 50% table virtual facet maps with the exact same angles and lowers.
notice the size and shape differences in the virtual facets.
There is no question there will be a difference in performance and sparkle size and shape and number(fire too).

But didn''t you automatically have to change the crown height to maintain the same crown angle with a different sized table?

Yes. But that does not make a meaningful difference in the comparison.

As for Sara''s question, I have the impression that you think that more virtual facets is better. This is very often not the case, as more virtual facets automatically means smaller virtual facets.

Live long,

 

[Lula]

Date: 3/1/2010 4:22:51 PM
Author: Paul-Antwerp

Date: 3/1/2010 2:58:15 PM

Author: ChunkyCushionLover

Date: 3/1/2010 2:26:28 PM

Author: Karl_K

To show you what I am talking about here is a 57% table vs 50% table virtual facet maps with the exact same angles and lowers.

notice the size and shape differences in the virtual facets.

There is no question there will be a difference in performance and sparkle size and shape and number(fire too).

But didn't you automatically have to change the crown height to maintain the same crown angle with a different sized table?

Yes. But that does not make a meaningful difference in the comparison.


As for Sara's question, I have the impression that you think that more virtual facets is better. This is very often not the case, as more virtual facets automatically means smaller virtual facets.


Live long,

Thanks Diagem and Paul for your responses to my questions.

Diagem, I can see the changes in the facet shapes that you pointed out. That was helpful.

Sure, Paul, on its face, it seems that more virtual facets would be better, but not if more means smaller -- because then wouldn't you have lots of fire "events," but much of it would be too small and splintery to perceive with the human eye? And that would mean there's a point of diminishing returns to adding more and more virtual facets?

 

[Paul-Antwerp]

Date: 3/1/2010 12:59:57 PM
Author: sarap333
There are some threads in the PS archives that go into this ''fire at the expense of brilliance'' and vice-versa argument. I don''t have time now to do an extensive search, but here''s one I found doing a quick search:
2005 thread

Sara, I feel very old now that I see that we already talked about this five years ago.

I think that the concept of brightness and fire being enemies originates from assessment of stones in the offices of diamantaires. These offices always are brightly lit, with north-facing windows and the stones are often examined under a desklamp. These circumstances are horrible for the observation of fire.

There, a bright stone clearly shows as a bright stone.

In these circumstances, the only stones showing a lot of fire were the ones that had a lot of light leakage, I guess. Obviously, these stones were not the brightest either. And very often, these were extreme steep/deeps (as we call them now), but in those days, most diamantaires in their observation paid more attention to the crown than to the more difficult to assess pavilion.

This has probably led to two ''universal truths'', repeated in many gemological textbooks, but in my view incorrect:
- brightness is the enemy of fire,
- fire is a result of smaller table/higher crown and/or higher crown angle.

Reality is that a bright stone in an office-environment will be very fiery in other lighting, for instance a dimly lit restaurant or a theater.

Live long,

 

[Karl_K]

Date: 3/1/2010 3:03:17 PM
Author: sarap333
Thanks, Karl! But, I had the same question as CCL - doesn''t changing the table to that degree require some adjustment in the other angles?

upper girdle angle changes, crown height changes. CA/PA/LGF angle are all the same.

 

[Karl_K]

Date: 3/1/2010 4:35:22 PM
Author: sarap333

Sure, Paul, on its face, it seems that more virtual facets would be better, but not if more means smaller -- because then wouldn''t you have lots of fire ''events,'' but much of it would be too small and splintery to perceive with the human eye? And that would mean there''s a point of diminishing returns to adding more and more virtual facets?

If they get to small they become ineffective is correct.
With large ones you get less events.
Med. sized is a good balance between effectiveness and frequency for a lot of lighting.

 

[Rockdiamond]

I think the amount and size of virtual facets is another aspect that goes to opinion.
Many fancy colored radiants and cushions have tiny virtual facets- resulting in the "bucket of crushed ice" look.
Some people love this, some don''t- but as in so many other aspects of a diamond''s cut, opinion plays a role.
I loved reading Paul''s posts here ( yes Paul we''re getting old, but it''s not that bad if one considers the alternative)
Part of what I read that I liked was the there are "rules" that may seem to be universally accepted when in fact, it''s not "black and white"

 

[Karl_K]

Date: 3/1/2010 5:37:39 PM
Author: Rockdiamond

Many fancy colored radiants and cushions have tiny virtual facets- resulting in the 'bucket of crushed ice' look.

Some people love this, some don't- but as in so many other aspects of a diamond's cut, opinion plays a role.

True but that does not change the fact they are ineffective at returning light in some lighting compared to others.
It is a bad comprimise for performance but a good one for color.
It allows there to be more of them on the market by creating fake fancies from lighter colored material.

 

[Rockdiamond]

Oh my...fake diamonds?

Sorry, but I had to laugh at that one Karl.
A diamond''s exhibiting color is desirable for some people.
In some manner, this is the basis for my criticism of judging a diamond using light return as a barometer. Stones with more color will, by their very nature, return less light compared to colorless.

Some people may prefer Fancy Vivid Yellow- that does not make a "U-V Range, Light Yellow " fake. ( the part in bold is GIA''s terminology, not mine)

Furthermore, colorless diamonds cut this way can be extremely desirable to many people as well.
Again, what may be proven with a light return analysis can be dis-proven when you show actual stones to actual people.


This does not mean what you may prefer is not gorgeous. It may very well be.
Just that other types of cut, ones that you may not prefer, can also be very beautiful to a large percentage of interested people viewing the diamonds.

 

[ChunkyCushionLover]

Date: 3/1/2010 7:21:55 PM
Author: Rockdiamond
Oh my...fake diamonds?

Sorry, but I had to laugh at that one Karl.
A diamond's exhibiting color is desirable for some people.
In some manner, this is the basis for my criticism of judging a diamond using light return as a barometer. Stones with more color will, by their very nature, return less light compared to colorless.

Some people may prefer Fancy Vivid Yellow- that does not make a 'U-V Range, Light Yellow ' fake. ( the part in bold is GIA's terminology, not mine)

Furthermore, colorless diamonds cut this way can be extremely desirable to many people as well.
Again, what may be proven with a light return analysis can be dis-proven when you show actual stones to actual people.


This does not mean what you may prefer is not gorgeous. It may very well be.
Just that other types of cut, ones that you may not prefer, can also be very beautiful to a large percentage of interested people viewing the diamonds.

Rd,

Karl was referring to the situation where if a piece of rough were cut as a cushion or round it would only achieve the grade of light yellow.
However, by choosing a cut with inferior light return like a radiant the same rough may now achieve a fancy color grade and sell for a higher price.
These stones sacrifice sparkle and white light return for color improvement so that they can fetch a higher price as fancy yellows.

I don't know if this is as common but even the same outline shape stone on the border of Light Yellow/Fancy couldn't it also be cut deeper for a longer ray path to make the Fancy grade?
Now not only does the stone cut this way have worse light return but now also costs the consumer more.

 

[soontomarry2]

A lot of online dealers seem to provide IS or ASET images with their stones.
Is there an online guide that explains what to look for in these images and
what the different colors mean? Do brick and mortar stores generally offer
these images? Can they take these images in the store?

Instead of gumming up this thread to much, are there any online guides that
discuss dispersion, brilliance, brightness, firey-ness, and scintillation?

There are some acronyms used in the replies above, I believe RB = round
brilliant. What does FIC, BIC, TIC, and OEC mean? What does star length mean?

I really appreciate the 3 step approach outlined above. Some of the stones I
have looked at are above 2, some below 2. I will be sticking to those below
2. For those below 2, what does the value converge too for the best cut? Does
it converge to 0? Is obtaining a 0 realistic or even possible? One stone I am
eyeing scored a 1.3, is this a decent distance below 2, or if I can, should I
attempt to find something with even a lower value?

Finally, many have mentioned that it is best to see the stone in person even
if the cut angles and numbers are what you are looking for. When it comes to
online retailers, how do you see the stone? Is it possible to have the stone
shipped to you before you buy it? Or, is the only way to see the stone is to
buy it in full, then have it shipped to you.

If it isn''t what you are looking for then you must ship it back within the
return period and get a full refund? If it is what you are looking for, is it
generally your responsibility to arrange it''s shipment to the ring
manufacturer for mounting, or do you generally ship it back to the diamond
seller and then ship it to the ring manufacturer?

I''m sorry for such a long a post, thanks for your help everyone.

 

[Lula]

Hi, soontomarry,
Here is a link to the Pricescope diamond education tutorial. This will help you define TIC, BIC, etc., and provide you with a wealth of information on what the HCA score means, and how to read a grading report.

Tutorial

A few bricks and mortar stores may offer tools such as Idealscope, ASET, star/hearts viewers for Hearts & Arrows stones, etc., but the majority don't, from my experience. Some consumers have purchased their own Idealscopes and taken them with them to stores to view the store's stones. I can imagine there'd be some sales staff that would object to that, though, or dismiss it as useless.

Some consumers who buy diamonds from online vendors have the diamond set by the online vendor and shipped to them. Others have the stone shipped to them unset. The majority of online vendors who you see recommended here have liberal return policies. So, yes, you would order the diamond, pay for it, have it shipped to you, and then you can see it in person and have it appraised by an independent appraiser if you'd like.

Yes, shipping can be expensive, and having a diamond appraised costs money, too, approximately $100-$150 in my part of the country, but these costs are well worth the peace of mind they provide, and are a relatively small percentage of the total cost of the diamond and setting.

Check the shipping and return policies of any online vendors you're considering working with. They do vary slightly from vendor to vendor. Some vendors cover the cost of shipping the diamond to you, but not the return shipping if you decide to send it back.

If you decide to buy a stone online and have it shipped locally, make sure you check to see what stores in your city will set a diamond that you supply, and how much they will charge to set the diamond (typically $100 - $200).

Many online vendors carry lovely settings in white and yellow gold and platinum. Typically the easiest thing to do is have the online vendor set your stone in one of their settings. So make sure you take a look at what the vendor has available for settings, and how their setting process works -- e.g., how long it takes, sizing, etc. And, yes, you may first order the stone, get it appraised locally, decide to keep it, and either ship it back to the vendor and the vendor will ship it to the setting manufacturer or the vendor will give you directions on how to ship your stone to the manufacturer.

Most important to know is that the vendors recommended on Pricescope are happy to answer your questions, and will work with you to help you find the perfect ring -- so don't be afraid to e-mail or call them.

Good luck, and you might want to start a new thread with any other questions, so that they don't get lost in this thread.

 

[Paul-Antwerp]

Date: 3/1/2010 5:37:39 PM
Author: Rockdiamond
I think the amount and size of virtual facets is another aspect that goes to opinion.
Many fancy colored radiants and cushions have tiny virtual facets- resulting in the ''bucket of crushed ice'' look.
Some people love this, some don''t- but as in so many other aspects of a diamond''s cut, opinion plays a role.
I loved reading Paul''s posts here ( yes Paul we''re getting old, but it''s not that bad if one considers the alternative)
Part of what I read that I liked was the there are ''rules'' that may seem to be universally accepted when in fact, it''s not ''black and white''

Thank you, David, but do not hold your breath.

When I am doubting and attacking ''universal truths'', it generally concerns old-time-thinking of the industry. Reading your posts, I see most of your opinions exactly being based upon such traditional ''truths''.

At the same time, a discussion forum like PS indeed creates new knowledge and ''truths'', of which I embrace at least 80%, but at the same time, I am sure that this new reality is also creating about 20% of incorrect ''rules''.

Unfortunately, I do not see you embracing the 80% of undeniable reality. Therefore, may I ask you not to twist my words, so that they seemingly are supporting your opinions.

Live long,

 

[Paul-Antwerp]

Date: 3/1/2010 4:59:09 PM
Author: Karl_K

Date: 3/1/2010 4:35:22 PM
Author: sarap333

Sure, Paul, on its face, it seems that more virtual facets would be better, but not if more means smaller -- because then wouldn''t you have lots of fire ''events,'' but much of it would be too small and splintery to perceive with the human eye? And that would mean there''s a point of diminishing returns to adding more and more virtual facets?

If they get to small they become ineffective is correct.
With large ones you get less events.
Med. sized is a good balance between effectiveness and frequency for a lot of lighting.

I find your statement, Karl, much too blunt and too general. Overall, I think that the presence of some large virtual facets is a bonus, and should not be dismissed. Part of this is also personal preference, and very difficult, if not impossible, to judge online.

And let us not forget that all this is size-related.

Live long,

 

[Lorelei]

Date: 3/1/2010 10:02:05 PM
Author: sarap333
Hi, soontomarry,


Good luck, and you might want to start a new thread with any other questions, so that they don''t get lost in this thread.

Hi Soontomarry,

Please go ahead and start a new thread as Sara suggests then we can answer all your questions there, once you do we can address each issue and make it a thread we can also use to help others as your questions do come up frequently.

 

[Regular Guy]

I bothered about this discussion last night, looking up some old threads. Although I found myself ultimately unable to get the basic point well enough to intuitively enough understand it...combined with Garry''s not having joined the discussion...where you say Paul...

Date: 3/1/2010 4:39:42 PM
Author: Paul-Antwerp

Date: 3/1/2010 12:59:57 PM
Author: sarap333
There are some threads in the PS archives that go into this ''fire at the expense of brilliance'' and vice-versa argument. I don''t have time now to do an extensive search, but here''s one I found doing a quick search:
2005 thread

Sara, I feel very old now that I see that we already talked about this five years ago.

I think that the concept of brightness and fire being enemies originates from assessment of stones in the offices of diamantaires. These offices always are brightly lit, with north-facing windows and the stones are often examined under a desklamp. These circumstances are horrible for the observation of fire.

There, a bright stone clearly shows as a bright stone.

In these circumstances, the only stones showing a lot of fire were the ones that had a lot of light leakage, I guess. Obviously, these stones were not the brightest either. And very often, these were extreme steep/deeps (as we call them now), but in those days, most diamantaires in their observation paid more attention to the crown than to the more difficult to assess pavilion.

This has probably led to two ''universal truths'', repeated in many gemological textbooks, but in my view incorrect:
- brightness is the enemy of fire,
- fire is a result of smaller table/higher crown and/or higher crown angle.

Reality is that a bright stone in an office-environment will be very fiery in other lighting, for instance a dimly lit restaurant or a theater.

Live long,

I don''t know that I do see the origins where you see them.

Look, for example, at this thread. You are on page 1, Paul. I really only know the discussion is relevant by the linked page 3. Although I don''t get it, I am not inclined to think the source of the perception goes to bad lighting in some guy''s office, but this is all 4th hand from my point of view.

I do, however, note reading here only recently about folks looking for high crowns and such, suspect the source of such threads is also this related idea, and I suspect that this particular discussion...if intended to put the death knell to such ideas, will not have done it...not that I am not enough the advocate of science that I am not specifically stepping in here...because I do like to see ideas looking for their proper recognition see the light of day.

 

[Karl_K]

Date: 3/2/2010 5:38:18 AM
Author: Paul-Antwerp

Date: 3/1/2010 4:59:09 PM

Author: Karl_K

Date: 3/1/2010 4:35:22 PM

Author: sarap333


Sure, Paul, on its face, it seems that more virtual facets would be better, but not if more means smaller -- because then wouldn''t you have lots of fire ''events,'' but much of it would be too small and splintery to perceive with the human eye? And that would mean there''s a point of diminishing returns to adding more and more virtual facets?

If they get to small they become ineffective is correct.

With large ones you get less events.

Med. sized is a good balance between effectiveness and frequency for a lot of lighting.

I find your statement, Karl, much too blunt and too general. Overall, I think that the presence of some large virtual facets is a bonus, and should not be dismissed. Part of this is also personal preference, and very difficult, if not impossible, to judge online.


And let us not forget that all this is size-related.


Live long,

Hi Paul,
That it is very over simplified is correct.
But with in the context of the question not that bad.
Some large and some small VF''s can balance out a diamonds performance.
Some cuts traditionally have more of one size than another which gives them their expected look. ie: EC: large and very large are expected.

Yes it is size dependent but....
What works well for a .75 will in general work well for a 2ct.
That might not be so for a .25ct and a 5ct.
In some ways I agree with using absolute size to rate VF''s but the relative size in a given diamond is important also.

 

[Rockdiamond]

Date: 3/1/2010 9:35:05 AM
Author: Paul-Antwerp
Dancing Fire,


In order to answer your question, I have to give my view on other subjects raised in this thread first. And if I consider the complete picture, this will also affect some more general points, that often are raised, but that I find too much of a generalisation.


So, if you wish, bear with me for a very long post.


Soontomarry, the suggested cut values of niceice.com are interesting, but you need to understand their values and their limitations. Todd Gray of NiceIce (a regular poster here and a friend) uses these values as a first selection of the stones that he might call in for purchase. In fact, I think that his actual selection-values are even somewhat stricter. However, these values are only a first selection (actually rejection) for him, and is followed by analysis on various other tools and his own visual observation, with the latter being the most important.


As an answer to your questions, no, only being within these value-ranges does not guarantee that the stone will have the best cut possible, as is demonstrated by the fact that NiceIce performs a lot of extra analyses and rejections after this initial rejection/selection.


Also, yes, there are most probably other combos outside of these ranges, depending somewhat on personal preference, and the list of NiceIce clearly reflects their personal preference and their search for the ultimate best in their eyes.


The pavilion angle stated by NiceIce as such is not too restrictive, since the correctness of the pavilion angle is the main driver of light return, but again, this choice clearly reflects the very selective criteria of NiceIce.


Stone-Cold, if you say that you can basically dismiss the numbers if IS/ASET is available, I have my doubts. I would definitely suggest using both in tandem as a minimum, especially with the numbers generally coming from an independent source (the grading-lab) and the pictures coming from the vendor. It took us very long to master our picture-taking and I see many vendors still struggling. As such, I find it very hard to read certain IS/ASET''s since I cannot assess the photographic set-up.


As for your call to widen the table-range, this is dependent upon personal taste, and basically covered in my answer to Soontomarry above.


Dreamer and CCL, you are right in your preference for the HCA as a first selection-tool, but I think that Todd''s list of values probably comes to the same or a slightly stricter result in a much faster elimination.


FB and Wink, your discussion about the range being 55-57 or 53-57 is dependent upon personal preference. However, there seems to be an undertone in your posts that a smaller table correlates with the stone exhibiting more fire. While I cannot say with 100% certainty that this assessment is incorrect, I always had serious doubts about it, because it simply does not seem logical to me that one basic parameter dictates fire so much, while we need all the proportions working together to create brightness. Let me explain further.


To me, the assessment that a smaller table/higher crown improves fire is still based upon the old gemological rule that brightness (brilliance) is the enemy of fire. The latter, old rule has been proven to be out-of-date. Brightness and fire can be present in the same stone, and the observation of fire and not brightness depends more upon the lighting environment, and less on the stone.


With the basis of the rule gone, I seriously doubt every assessment based upon ''A smaller table/higher crown creates more fire''. As such, for me, the FIC does not exist either.


In my experience, light return is essential in the performance of a diamond. This, we combine with a very high optical symmetry, in which the shape of the contrast-pattern is actually less important than the crispness of the pattern. The crispness of the contrast-pattern is the basis for scintillation, which depending on the light environment and the observer can be viewed as dynamic brightness or dynamic fire.


Eventually, this leads me to the answer of DF''s question. Based upon the above, we have our own goal-set of proportions, which combined with our level of optical symmetry (and cooked in some very personal, secret Paul-sauce) leads to what we consider the best combo of all sparkle-factors of a diamond. Sure, cutting the same stone with a slightly smaller table probably could yield a diamond that appeals more to some individuals, it will even bring about a slightly higher yield from most rough, but it lessens the predictability/consistency of our brand.


My apologies for the long post. Congratulations to those who read until the end.


Live long,

Paul- The parts I underlined were what I was referring to.
Without question, people may have different taste- and what I read in your post that I did agree with was that taste does pay an important role.
I also agree with the observation of fire and brilliance is dependent on many factors - you mentioned the lighting environment.

I don''t feel that categorizing opinions as "old thinking" or "new thinking" is very productive. As demonstrated by the wild popularity of older style cuts, sometimes old ideas are timeless.

Likewise pejorative categorizations- like "fake fancies".

CCL- you are generalizing with no basis in fact.
There are a lot of cushions with extremely similar light and facet characteristics to some radiant cuts. So, some cushions and radiants are very similar.
You also insist on ignoring my point: light return is not the "end all be all" of beauty in diamond.
If so, we could state unequivocally that a D was "better" than a Fancy vivid Yellow.

Furthermore, your reasoning is faulty in that successful cutters of fancy cutters have to be able to combine color retention, with sparkle, fire, brilliance- and other aspects that go into making a beautiful stone. Is it your impression that it''s possible to get higher prices for worse looking stones simply because they have color? That''s simply not the case. Buyers of fancy colored diamonds look for sparkle, brilliance, attractive shape AND color.

IN fact, this is one areas where the newer cutting and plotting technology has a HUGE impact.
Cutters are able to plan more accurately, allowing them to saw octehedrons, and get two sale-able stones.
IN many cases the bottom, larger piece will have far more color. Many of the top pieces are more shallow- and have less color.
Modern cutting techniques allow some very beautiful stones to be cut from this shallow rough.
Even if it is U-V color.
Another great aspect is that this planning is profitability for the cutter. Since they can use the rough more efficiently, this results in lower prices for these stones.
Many people find these light colors quite beautiful. The net result is consumers getting larger diamonds at lower prices.
It''s not a simple question of trying to get maximum light return.
A U-V colored round might technically have better light return than a U-V radiant- yet the Radiant may be far more desirable in the market- and easier to sell.
Cutters need to cut stones people want to buy, or they''re out of business.

To the OP_ Sara''s suggestion was a good one- sorry if the threat took a tangent.
But from my perspective it also is valuable in answering your initial question as it seems clear that taste plays a role- so looking at different stones will serve consumers best.
Look at stones in the range Todd suggests as well as stones with slightly larger tables.
I''d also suggest seeing some GIA "VG" cut grade stones to see how they strike you.
If you find one you love, you can either spend less, or get a larger stone for the same budget.