H&A - pattern vs crispness?

[yssie]

CCL -

well - the quest for utterly, identically, absolutely perfect hearts is rather a futile one, no? Add the uncertainty that comes with the photography of those hearts through the viewer..

http://www.jamesallen.com/diamonds/E-VS ... 193966.asp

 

[Karl_K]

b) For any given size of diamond the greater the optical symmetry the greater the average virtual facet size.

maybe true, but the average EFFECTIVE virtual facet size can be larger depending on the lighting.
When you separate the effective and ineffective virtual facets which changes with lighting type the picture changes a bit.

 

[Karl_K]

Point b) is the main thing that is being emphasized by the examples provided by Karl K yet his examples also have different PA and LGF size so the appearance is being affected by those as well, arguably to an even larger extent.
VF crispness is not dependent on lgf length nor is it limited to RBs, it is only mildly related to PA in that under-table leakage produces mush

2) Scintillation in the near tolk RB and in most other cuts is most prominent in areas that strongly return light to the viewer (e.g. ASET RED).
depends on the lighting but is almost always under the crown facets where the med sized VF's live that will return the most number of visible scintillation events except in strong spot lighting or low light.
As a test rock a diamond quickly and see there the most events spear to be coming from, then repeat in 500 different lighting conditions.

 

[yssie]

b) For any given size of diamond the greater the optical symmetry the greater the average virtual facet size.

maybe true, but the average EFFECTIVE virtual facet size can be larger depending on the lighting.
When you separate the effective and ineffective virtual facets which changes with lighting type the picture changes a bit.

Intruding again here -
I don't understand what this means - what is an "effective VF" - do you mean VFs - or maybe the proportion of VFs - that leak/obstruct in different lights?

 

[Karl_K]

b) For any given size of diamond the greater the optical symmetry the greater the average virtual facet size.

maybe true, but the average EFFECTIVE virtual facet size can be larger depending on the lighting.
When you separate the effective and ineffective virtual facets which changes with lighting type the picture changes a bit.

Intruding again here -
I don't understand what this means - what is an "effective VF" - do you mean VFs - or maybe the proportion of VFs - that leak/obstruct in different lights?

Effective is returning or capable of returning light to the eye.
It is best observed but if you have further questions I can work on a reply.
View your diamond in very flat lighting, view your diamond in strong direction lighting(direct sun) and in candle light, then in light from direction; in each of the different lighting conditions the diamonds appearance will change as different virtual facets become effective.
In the direct lighting you will see a lot more small events than in the flat lighting in candle light you will see mostly large events and facet glare.

There was a picture the other day with a diamond over obstructed with the table area dead.
It had many ineffective virtual facets due to over obstruction.
Here is my virtual model of the diamond from the thread:

 

[yssie]

Thanks Karl, I'm sure I speak for everyone when I say that we consumers really appreciate the time and effort tradespeople put into this board, and this thread is one of many such examples

I'm fascinated by how my pet rocks 'work', but like with most things coming up with the right questions is half the battle! I'm glad we have Sara/Portree to dream them up for us


I see what you mean by ineffective VFs in that simulation
I have always assumed that whilst there may be changes in the way the stone handles light in different lighting the vast majority of the difference we see is in how our eyes perceive the emissions, your statements rather indicate that it is less an issue of perception

 

[ChunkyCushionLover]

Point b) is the main thing that is being emphasized by the examples provided by Karl K yet his examples also have different PA and LGF size so the appearance is being affected by those as well, arguably to an even larger extent.
VF crispness is not dependent on lgf length nor is it limited to RBs, it is only mildly related to PA in that under-table leakage produces mush

LGL changes the size and number of VFs as well as the observable versus unobservable VFs ratio. I don't know how one can discuss "crispness" and ignore the small VFs around the pavillion mains and their phase that may result in a lack of crispness. The CA/PA and LGF change the thickness of the arrows and the overall VFs pattern under the table which is not independant of optical symmetry concerns. Shown below three tolk rounds with 80% LGL versus one with 55% LGL taken from Peter Yantzer's presentation at the Infinity Symposium April 2010. All have perfect optical symmetry, a dramatic change in size and number of VFs and thus scintillation as a result of different LGL.



Why not show side by side a theoretical diamond with perfect symmetry and same CA/PA and LGF beside the real world example? this would emphasize the differences far better than two very different looking diamonds with quite different thickness in the VFs representing the pavillion mains.

2) Scintillation in the near tolk RB and in most other cuts is most prominent in areas that strongly return light to the viewer (e.g. ASET RED).
depends on the lighting but is almost always under the crown facets where the med sized VF's live that will return the most number of visible scintillation events except in strong spot lighting or low light.
As a test rock a diamond quickly and see there the most events spear to be coming from, then repeat in 500 different lighting conditions.

Scintillation is related to the number and size of VFs.
The number of VFs doesn't change with a change in lighting they are a fixed property of the diamond.
The angular range from which each of the the diamond's facets receive light which can be directed back to the viewer does not change either with lighting except where part of the lighting hemisphere is removed or blocked(remove the ASET red range 45 - 75 and the facet can only return light from green or blue part of the hemisphere back to the viewer).

 

[Karl_K]

CCL
The lighting determines the effective virtual facet count.
That is not the same as the total VF count.
See the above image it has a lot more ineffective virtual facets than the AGS count.
The AGS count is only accurate in one lighting and environment condition.
Frankly I have serious doubts about it being accurate at all.

 

[Lula]

b) For any given size of diamond the greater the optical symmetry the greater the average virtual facet size.

maybe true, but the average EFFECTIVE virtual facet size can be larger depending on the lighting.
When you separate the effective and ineffective virtual facets which changes with lighting type the picture changes a bit.

Intruding again here -
I don't understand what this means - what is an "effective VF" - do you mean VFs - or maybe the proportion of VFs - that leak/obstruct in different lights?

Effective is returning or capable of returning light to the eye.
It is best observed but if you have further questions I can work on a reply.
View your diamond in very flat lighting, view your diamond in strong direction lighting(direct sun) and in candle light, then in light from direction; in each of the different lighting conditions the diamonds appearance will change as different virtual facets become effective.
In the direct lighting you will see a lot more small events than in the flat lighting in candle light you will see mostly large events and facet glare.

There was a picture the other day with a diamond over obstructed with the table area dead.
It had many ineffective virtual facets due to over obstruction.
Here is my virtual model of the diamond from the thread:

Hey, wait a minute - that's my over-obstructed M you're talking about from the Contrast thread I was leaning over the diamond with the camera; worse, the lighting was low (late afternoon) and I was wearing a black t-shirt. All I needed to make it worse was Garry's legendary "big hairdo." I have to admit that I have a very hard time knowing how contrast, obstruction, and scintillation work together -- and now add crispness to that. There seems to be some minimal level of obstruction needed to make the patterning work -- whether that patterning is an OEC, H&A or a step cut; however, as we repeat often on PS, too much obstruction interferes with the diamond's ability to return light -- resulting in "ineffective virtual facets" (another new term).

yssie, I think this thread will generate a lot of new threads...my head is spinning.

I do think the important things I've learned so far are:
a) crispness is not limited to H&A patterning
b) crispness is influenced by the angles, but the angles only tell part of the story
c) crispness is related to contrast
d) not enough crispness = "mush"
e) oh, yeah, and lighting, lighting, and lighting have the biggest impact on a diamond's appearance!

But, I have another question about e). If a diamond is "crisp," shouldn't it look *"better" across all lighting conditions, i.e., have more effective virtual facets, than a diamond that is less crisp? Shouldn't crispness raise all boats?

* value-laden, subjective term warning.

 

[ChunkyCushionLover]

CCL
The lighting determines the effective virtual facet count.
That is not the same as the total VF count.
See the above image it has a lot more ineffective virtual facets than the AGS count.
The AGS count is only accurate in one lighting and environment condition.
Frankly I have serious doubts about it being accurate at all.

Karl,

I am not privy to the supporting information and proof that AGS used for the facet counts but considering that in the corresponding ASET30 images every facet(save for the areas of leakage) is capable of returning light to the viewer and thus being an effective VF(if large enough in size). The requirement that it receives light from its backward ray traced angle in the hemisphere from 45 - 90 (Red and Blue Range) would be satisfied.

The AGS presentation doesn't report the actual effective VFs from one particular lighting scenario, but instead considers potential lighting where the entire overhead range may be available. This to me is a prudent way of considering the problem, we live in a world of dynamically changing lighting not one of limited static lighting.

I beleive you have used lighting that illuminates facets from this entire hemisphere as well in the simulated lighting provided by your images.

You may argue that the absolute numbers may not be accurate but this doesn't change the fact that stones with shorter LGL and larger average VFs have less virtual facets.

CCL

 

[ChunkyCushionLover]

CCL
The lighting determines the effective virtual facet count.
That is not the same as the total VF count.
See the above image it has a lot more ineffective virtual facets than the AGS count.
The AGS count is only accurate in one lighting and environment condition.
Frankly I have serious doubts about it being accurate at all.

I don't know the parameters or lighting that example is simulated from but I doubt that light is available from the entire hemisphere nor is that an Ideal Tolk as used in the AGS simulation.

 

[Paul-Antwerp]

CCL and Karl,

I think that you are both partially right in what you present, but I fail to see the relationship to the crispness of the arrows-view.

Live long,

 

[ChunkyCushionLover]

Looking at various arrows-patterns, one can easily distinguish stones with a very crisp pattern, while in others the borderlines between white and red are relatively fuzzy. This is completely neglected in the traditional assessment of H&A, but it is important for the scintillation of the diamond. The fuzzy borders are caused by minutely small extra virtual facets on this location, a result of slightly less than optimal optical symmetry. These tiny extra virtual facets reduce the snappy on-off-effect of virtual facets when moving the stone, and it results in a clear difference in observed scintillation. At the same time, the tiny virtual facets do not contribute to the observation of fire.

Live long,

Paul the statement above seems logical to me and intuitive but the proof has not been provided yet.

Ideally I'd like to see a real world example of a diamond which passes HA as defined https://www.pricescope.com/journal/hearts_and_arrows_diamonds_and_basics_diamond_cutting/ which still exhibits this fuzziness or reduced scintillation you speak of.

In beleive it will be difficult for you to find such an example. If so then just choose one with decent complimentary CA/PA and LGF and that passes as AGS0 but is far from perfect optical symmetry.

1) How bad does the optical symmetry have to be to produce a significant and percetpible decrease in these properties?
2) Can you prove this claim with real world or theoretical side by side images where you isolate the optical symmetry and don't change the CA/PA and LGF?
--------------------------------------------------

I really am not convinced of anything in this thread thus far, as the examples shown are of diamonds with different CA/PA and LGF. If we are going to go beyond just brightness and attempt to consider the less understood and agreed upon properties of scintillation and fire than supporting proof should be more robust than shown thus far.

 

[Paul-Antwerp]

CCL,

The crispness in our patterns, as viewable in the H&A-viewer, is a result of our process, and is not directly related to the specific CA/PA or the LGF.

I am not in a position to show real-life negative examples, as it infringes forum-policies. It is, I think, the main reason why certain diamonds score consistently better in a pepsi-comparison-test, while there is no distinguishable difference in the online-information.

I fear also that Diamcalc is useless in assessing this.

Live long,

 

[Lula]

CCL,

The crispness in our patterns, as viewable in the H&A-viewer, is a result of our process, and is not directly related to the specific CA/PA or the LGF.

I am not in a position to show real-life negative examples, as it infringes forum-policies. It is, I think, the main reason why certain diamonds score consistently better in a pepsi-comparison-test, while there is no distinguishable difference in the online-information.

I fear also that Diamcalc is useless in assessing this.

Live long,

Thanks, CCL and Paul and Karl and yssie, for your continued input into this thread. My concern as someone who purchases diamonds and, perhaps more important at this stage of the game, occasionally advises other consumers about particular diamonds is twofold:

A) Is it possible to have a stone with perfect hearts that lacks crispness? In other words, perfect hearts does not guarantee crispness; the processes for producing perfect hearts and a high level of crispness may not be related? Or may not be related to the degree some of us consumers have assumed?

Reading back through Paul's responses, it seems the answer to this question is yes, am I correct?

CCL, it seems from your last post that you doubt this, or at least doubt this without more visual proof.

Certainly, the mantra around here for a long time has been if the hearts are perfect, the diamond will meet the criteria of H&A, and therefore have optimal optic symmetry and therefore optimal performance -- including maximum fire, scintillation and brilliance.

B) But if it is indeed possible to have a stone with perfect hearts and less-than-optimal crispness, then one place to see this would be through the arrows viewer? (I'm leaving aside in person visual inspection for the moment)?

One problem: Many vendors do not post photos of arrows.

Also, the H&A tutorial mentions assessing the arrows, but if memory serves me right, the tutorial emphasizes that if the hearts are cut correctly (pavilion) the arrows will follow. The hearts drive the cut quality, in other words.

Again, the mantra around here is that if your CA/PA, depth, table, etc., are complimentary, and the hearts meet H&A standards, you'll end up with a beautiful diamond.

I know there are many here who appreciate the technical discussions and graphics that delve into the physics of light return; however, as a consumer who often advises other consumers, my concern is giving responsible and accurate advice to other consumers.

I want to know first what crispness is (we've made headway on the definition, I think) and how to assess it. If the only way to assess it is through in-person "pepsi-tests" as Paul mentions, then fine. We always tell consumers to do this. Perhaps after this discussion, the average consumer will focus more keenly on the nature of and differences in scintillation and contrast among several stones. Then this thread will have helped a consumer become a better judge of what they are seeing in real life.

I, too, would prefer some real life examples as educational tools. But if the forum rules prohibit the posting and discussing of photos that could demonstrate this phenomenon of crispness (or the lack thereof), that will obviously limit the discussion, and perhaps limit the amount of help we can give consumers.

I don't know. It's frustrating. I see this "crispness" in my own diamond(s) and I know others do, too. Several of us have had discussions about it in other threads. Lynn B. mentioned several pages back that she owned one diamond that had "it" and one that didn't. But conveying what we see through definitions, education, examples, etc., so that others may benefit from it is proving to be pretty tough.

ETA: I know this discussion of crispness does not apply only to H&A. I guess I will go back and read Karl's step cut article. I imagine crispness is a key factor in producing a step cut with life vs one that is flat and one-dimensional-looking.

ETA(2): I re-read some of the last posts, and it seems that the arrows are not all that helpful in assessing crispness.

So we have a real phenomenon like crispness, which consumers can see, which adds in a positive way to the performance of a diamond, not just an H&A diamond, and no objective tools to assess it -- I hate that!

 

[Karl_K]

CCL,

I am not in a position to show real-life negative examples, as it infringes forum-policies. It is, I think, the main reason why certain diamonds score consistently better in a pepsi-comparison-test, while there is no distinguishable difference in the online-information.

Live long,

Write an article then you can show whatever you want.
The first thing you need to do is define your terms
then present proof it exists
show how to identify it (frankly I think that any h&a scope doesn't have the resolution to show it, but I will consider your thoughts)

Then work on sorting out how much is enough and how much is crisp enough is the next step.

Real proof would be finding some crisp stones and various levels of non-crisp stones and doing a double blind study.
Until then it is a nice theory that I think may have some merit.

 

[ChunkyCushionLover]

CCL,

I am not in a position to show real-life negative examples, as it infringes forum-policies. It is, I think, the main reason why certain diamonds score consistently better in a pepsi-comparison-test, while there is no distinguishable difference in the online-information.

Live long,

Write an article then you can show whatever you want.
The first thing you need to do is define your terms
then present proof it exists
show how to identify it (frankly I think that any h&a scope doesn't have the resolution to show it, but I will consider your thoughts)

Then work on sorting out how much is enough and how much is crisp enough is the next step.

Real proof would be finding some crisp stones and various levels of non-crisp stones and doing a double blind study.
Until then it is a nice theory that I think may have some merit.

It may be a nice theory but the applications of this thread are severely limited without further proof:

1) It won't help differentiate between superideals that satisfy the HA standard. I question whether the differences attributable to higher than HA standards of optical symmetry if any are observable. Many posters already question whether they can see significant differences between near HA versus superideal stones. Adding another higher level of HA from "crispness" amongst stones that already satisfy this lofy standard from the HA images would be ever harder to observe and prove.

2) It may differentiate superideals vs non superideals(which still get AGS 0 for brightness but not HA)

Differences attributable to a lower level of optical symmetry may very well affect scintillation and fire in some lighting.This remains to be proven as overall appearance cannot be seperated without a controlled study from differences in the average CA/PA and LGF%. Even in this thread one consumer's observations while comparing two AGS 0 stones while helpful are incomplete as we are not aware of crucial proportions and angles of the two diamonds being compared.

3) The comments and theory presented here provide for other observable properties other than leakage and brightness that differentiate near tolk from less fine makes with less than complimentary CA/PA combinations.

Shown below is two slides from an AGS presentation on Fire at the Infinity Dealers Conference on April 2010.

As can be seen the change in CA/PA combination has a significant affect on brightness and fire, arguably much more so than the moderate differences in symmetry being discussed here. Both the Tolk and "Inferior Make" were simulated with perfect optical symmetry.

The third and fourth images are the forward and reverse disperion maps related to fire, the legend for the colors is shown below them. Yellow shows the greatest dispersion followed by orange.

ASET30 = Cone of obstruction(blue) from 105 - 75
ASET40 = Cone of obstruction(blue) from 110 - 70

The second row of images are when the stones are tilted 15 Degrees.

First the Tolk Ideal



And a "Less Fine Make"



Here is the legend on interpreting the Disperion maps:

If you see yellow in a fire map it means that the average dispersion, at the close observation point of 9.84 inches, is greater than 5.8 millimeters at your pupil. If you see orange it means that the average dispersion is between 3.8 and 5.79 mm etc.

 

[yssie]

As can be seen the change in CA/PA combination has a significant affect on brightness and fire, arguably much more so than the moderate differences in symmetry being discussed here. Both the Tolk and "Inferior Make" were simulated with perfect optical symmetry.

This is in question?

There is no magic to those last examples - diamond RI stays the same, beam a white ray onto the crown, some small portion is reflected as glare and majority of energy continues into the stone in the refracted ray, which then reflects internally (and each reflection expands the diametre of the dispersion since angles of incidence are slightly different, refracts out of the diamond - the more diamond material, the longer the ray path within the stone, the longer the ray path the greater the diametre of dispersion

Same argument as stone size increases, for that matter

 

[yssie]

ETA: incident colours*

 

[ChunkyCushionLover]

As can be seen the change in CA/PA combination has a significant affect on brightness and fire, arguably much more so than the moderate differences in symmetry being discussed here. Both the Tolk and "Inferior Make" were simulated with perfect optical symmetry.

This is in question?

There is no magic to those last examples - diamond RI stays the same, beam a white ray onto the crown, some small portion is reflected as glare and majority of energy continues into the stone in the refracted ray, which then reflects internally (and each reflection expands the diametre of the dispersion since angles of incidence are slightly different, refracts out of the diamond - the more diamond material, the longer the ray path within the stone, the longer the ray path the greater the diametre of dispersion

Same argument as stone size increases, for that matter

The point in posting the fire maps is the same point as I made before, CA/PA matter in both dispersion and scintillation and overshadow slight differences in optical symmetry. That is why I don't accept the images shown is this thread as being sufficient proof in support of Paul's theory. As Karl already pointed out if we are going to break new ground here it is likely an article will be required with a proper controlled study and defined terms.