H&A - pattern vs crispness?

[haflc]

I just started doing some research into diamonds, especially H&A, and I am finding out new information every day that make me refocus my search parameters. (symmetry, cut angles and proportions , crispness)

It's not very easy comparing apples to apples, since most B&M shops do not have a wide variety of stones within a range of color and clarity, especially H&A.

1. In terms of visualizing the Arrows pattern, I'm assuming that obstruction is not a good thing. Is that correct?
2. How are we to know based on internet H&A images how much obstruction there will be?
3. And are there parameters that will allow us to evaluate how to get the best performance in a ring in regards to obstruction? (Will using the HCA give all the information one needs?)

Thanks

Thanks.

 

[Karl_K]

Thanks again, Karl, for the great images. They demonstrate the concept of crisp optical borders very well. I guess I never realized how much of a stone's visual beauty is controlled by virtual facets, and how much slight variations in cutting can affect a stone's appearance.

virtual facets and how they react to light defines diamond performance.
The angles of the diamond control how they react and gives them their shape.
My article on the subject is about step cuts but will give you the idea:
https://www.pricescope.com/journal/virtual-facets-and-patterns-discussion-about-step-cuts

 

[Hest88]

Very interesting. I'd really like to see a vid or photos of two representative stones side by side. The renditions are great, but I'm curious to see a "real life" comparison.

 

[stone-cold11]

I just started doing some research into diamonds, especially H&A, and I am finding out new information every day that make me refocus my search parameters. (symmetry, cut angles and proportions , crispness)

It's not very easy comparing apples to apples, since most B&M shops do not have a wide variety of stones within a range of color and clarity, especially H&A.

1. In terms of visualizing the Arrows pattern, I'm assuming that obstruction is not a good thing. Is that correct?
2. How are we to know based on internet H&A images how much obstruction there will be?
3. And are there parameters that will allow us to evaluate how to get the best performance in a ring in regards to obstruction? (Will using the HCA give all the information one needs?)

Thanks

Thanks.

1. No. The obstruction mentioned here is allowable, even sought after. It allows for the viewing of the arrows in H&A, else why is it call H&A.

2. You do not see obstruction issue with a H&A scope, you see it with idealscope. It has issue when other facets other than the main pavilion facets, the arrows, goes black.

3. HCA, within the AGS Ideal/GIA Ex grade generally will not have obstruction issue. But that is based the assumption of perfect symm and only 4 average numbers. Idealscope image will tell more.

 

[Andelain]

Very interesting. I'd really like to see a vid or photos of two representative stones side by side. The renditions are great, but I'm curious to see a "real life" comparison.

I may be able to help with that in a months or so. I just bought a loose stone with really 'tight' numbers on the Helium report, and now I'm looking for one that's also an AGS ideal, but a weak report. I want to be able to compare them side by side, and plan to take pics if I can.

 

[yssie]

Thanks again, Karl, for the great images. They demonstrate the concept of crisp optical borders very well. I guess I never realized how much of a stone's visual beauty is controlled by virtual facets, and how much slight variations in cutting can affect a stone's appearance.

virtual facets and how they react to light defines diamond performance.
The angles of the diamond control how they react and gives them their shape.
My article on the subject is about step cuts but will give you the idea:
https://www.pricescope.com/journal/virtual-facets-and-patterns-discussion-about-step-cuts

Fun article, addresses what virtual facets are - don't know that I agree with a couple of their assertions wrt what colours the eyes see in diff circumstances but gives a good overview of refraction.

 

[yssie]

Oops, I forgot the article!

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

 

[Lula]

Very interesting. I'd really like to see a vid or photos of two representative stones side by side. The renditions are great, but I'm curious to see a "real life" comparison.

I may be able to help with that in a months or so. I just bought a loose stone with really 'tight' numbers on the Helium report, and now I'm looking for one that's also an AGS ideal, but a weak report. I want to be able to compare them side by side, and plan to take pics if I can.

Hmm, this will be an interesting comparison! Do you have a link you can share with us for the "tight" stone, Andelain? Inquiring minds...

 

[Andelain]

Very interesting. I'd really like to see a vid or photos of two representative stones side by side. The renditions are great, but I'm curious to see a "real life" comparison.

I may be able to help with that in a months or so. I just bought a loose stone with really 'tight' numbers on the Helium report, and now I'm looking for one that's also an AGS ideal, but a weak report. I want to be able to compare them side by side, and plan to take pics if I can.

Hmm, this will be an interesting comparison! Do you have a link you can share with us for the "tight" stone, Andelain? Inquiring minds...

Sure, here's the tight one

http://goodoldgold.com/diamond/6883

It's already on it's way to me and as soon as Jon gets back from vacation I'm going to ask him about one that I've spotted that I think may be much looser in the azimuth angles. I'm hoping I'm right about the other one since it's close in color, and I may want to mount them together in something someday.

Here's a thread where I was using the same stone as an example trying to find out what might be the 'perfect' stone on paper, and what started as a question on crown and pav angles, LGF's etc, turned into a goof lesson (for me, at least) about a lot more.

post2640596.html#p2640596

 

[Paul-Antwerp]

Thanks, Paul - your answers have clarified what you mean by "crispness"; however, I'm still curious about a few more things -- see my questions to your answers below.

Q.1: regarding the judgment of crispness through photographs. It is obviously easier to make this judgment in real life than through photographs. Various photo-setups make comparisons difficult and some vendors are not spending sufficient time in focusing and centering while photographing their stones. Then again, I would not dismiss the judgment of photographs. Crispness or the lack of is easy to see, once you start paying attention to it. So, if I'm reading this response correctly, one can train one's eye to look for a stone's level of crispness, regardless of the photo setup/quality -- within limits, of course? Can you give us some idea of what you pay attention to when assessing crispness? I know this is tough without relying on photos (forum rules) but if there is a way to describe what you're seeing in words, please share.

Let me take all these questions one at a time.

Yes, one can pay attention to a stone's level of crispness, and I suggest it starts with assessing the arrows-view. The arrows are a very important contrast-pattern, because with the slightest movement, the arrows have a great chance of showing a lot of fire. In that sense, I really think that you should check a true arrows-view, not an ideal-scope. The setup is theoretically the same, but in the H&A-viewer, the border between red and white is much better defined than the border between pink and black in the ideal-scope.

Of course, this is only a first step, and Karl is right in mentioning that it could lead to false positives. Then again, I am unsure if video is the solution. At some point in time, one has to accept that real-life-observation is necessary.

Live long,

Sorry, I do not master the quotes in PS 2.0 yet.

 

[Paul-Antwerp]

Thanks again, Karl, for the great images. They demonstrate the concept of crisp optical borders very well. I guess I never realized how much of a stone's visual beauty is controlled by virtual facets, and how much slight variations in cutting can affect a stone's appearance.

I know that I can see crispness in my own diamond -- so the eyes, when trained, can make a visual assessment. But we still need to help consumers find the best stones online, sight unseen, so I'm still pushing for ways to assess a stone's potential crispness using the tools available to us as consumers. In that vein, when looking at a diamond online and trying to assess it for "crispness," [color=#FFFF00[color=#FF4000]]would it be wise to take a look at the helium report and check on the deviations (variance) in crown, pavilion, etc.? [/color][/color]Helium gives us a picture of how tightly the stone is cut, right? And I may be wrong, but it seems logical that a tightly cut stone would be more likely to have crisp optical borders?

Agghhh, I just feel like I'm stumbling around here, looking for the right terminology!

I do not think that it is easy to assess this in a Helium-measurement, since it is a combination of angles and azimuth. In that way, the Helium-analysis becomes too complicated, and limiting it to assessing the angles is incomplete.

Live long,

 

[Daniel S.]

A diamond can have picture perfect arrows but never show them except in a very close view forcing over obstruction to darken both the shafts and heads of the arrows.

Karl, what exactly is over obstruction? Is this simply the obstruction from a viewer's head at a short distance?

 

[Karl_K]

A diamond can have picture perfect arrows but never show them except in a very close view forcing over obstruction to darken both the shafts and heads of the arrows.

Karl, what exactly is over obstruction? Is this simply the obstruction from a viewer's head at a short distance?

yep and even in some cases putting on a dark face mask

 

[Lula]

Thanks, Paul - your answers have clarified what you mean by "crispness"; however, I'm still curious about a few more things -- see my questions to your answers below.

Q.1: regarding the judgment of crispness through photographs. It is obviously easier to make this judgment in real life than through photographs. Various photo-setups make comparisons difficult and some vendors are not spending sufficient time in focusing and centering while photographing their stones. Then again, I would not dismiss the judgment of photographs. Crispness or the lack of is easy to see, once you start paying attention to it. So, if I'm reading this response correctly, one can train one's eye to look for a stone's level of crispness, regardless of the photo setup/quality -- within limits, of course? Can you give us some idea of what you pay attention to when assessing crispness? I know this is tough without relying on photos (forum rules) but if there is a way to describe what you're seeing in words, please share.

Let me take all these questions one at a time.

Yes, one can pay attention to a stone's level of crispness, and I suggest it starts with assessing the arrows-view. The arrows are a very important contrast-pattern, because with the slightest movement, the arrows have a great chance of showing a lot of fire. In that sense, I really think that you should check a true arrows-view, not an ideal-scope. The setup is theoretically the same, but in the H&A-viewer, the border between red and white is much better defined than the border between pink and black in the ideal-scope.

Of course, this is only a first step, and Karl is right in mentioning that it could lead to false positives. Then again, I am unsure if video is the solution. At some point in time, one has to accept that real-life-observation is necessary.

Live long,

Sorry, I do not master the quotes in PS 2.0 yet.

Thanks again, Paul, for answering my questions. I have learned a lot from this thread. It's interesting you mention looking at the arrows view, because of all the information available on stones posted here, the arrows view is usually the image I pay the least attention to. I will pay more attention now and see if I can train my eye to see subtle differences (keeping Karl's caution in mind).

It does make perfect sense that the arrows would play an important role in contrast and fire -- I often tip my diamond a certain way in sunlight (in the car -- bad girl!) so the light can illuminate an arrow and -- bam! -- I'll see a giant burst of fire. I'm sure I'm not the only PS'er who does this.

This thread has also increased my understanding about appreciate the role that contrast plays in the beauty of a diamond, and how crispness relates to contrast.

 

[Lula]

Oops, I forgot the article!

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

Looks like a great article, yssie. Thanks!

 

[Paul-Antwerp]

Thank you, Sara, for posting that real-life-example of how an obstruction-area (arrows) is a huge producer of fire with minimal movement of the stone.

This may also help you understand why I am so skeptical about certain traditional beliefs about fire.

Live long,

 

[Karl_K]

It does make perfect sense that the arrows would play an important role in contrast and fire -- I often tip my diamond a certain way in sunlight (in the car -- bad girl!) so the light can illuminate an arrow and -- bam! -- I'll see a giant burst of fire. I'm sure I'm not the only PS'er who does this.

Sure in the right lighting and tilting it just so you can get a nice fire display off the arrows.
Find the tipping point from obstruction to fire and it can even do so with small movement.
I however would be cautious about drawing any conclusions from it about the diamonds light return the rest of the time.
For any set of virtual facets you can find a lighting condition that is best for them, I can also design the virtual facets in a stone for a given type of lighting.

 

[Paul-Antwerp]

I do not fully understand what you are saying, Karl, but it sure leaves a bad taste.

It is a simple optical reason why an obstructed area, notably the arrows, are very firey when slightly moving the diamond. Moving the stone further, these virtual faces will become very bright.

Your reply seems to say that it means nothing, while it is the basis of a great diamond.

Your reply also seems to say that this is mainly dependent upon light-condition. It is not. This fire can be observed in very fire-unfriendly circumstances.

Live long,

 

[Karl_K]

Paul take it in context....
sunlight in a car...tilting it to fire a set of virtual facets off an on...
Cant be used to draw conclusions about a diamonds performance in other lighting.

The arrows being the largest virtual facets will show fire in some conditions the smaller virtual facets will not and the reverse is also true.
So I do agree with you that the arrows will show fire in lighting that if fire unfriendly for the rest of the virtual facets. The same could be said for any of the virtual facets.

 

[Karl_K]

Taking it one step further and it supports Paul's crispness theory my opinion the virtual facets I pointed out below and their twins are the virtual facets most likely to show fire across the most lighting conditions on an RB.

 

[Paul-Antwerp]

Karl,

You are making presumptions based upon virtual design, which automatically leads to crispness. In real life, such presumptions are meaningless. Plus, you do not understand at all what I am refering to when Sara's stone exhibits extreme fire in fire-unfriendly situations.

Live long,

 

[Karl_K]

Karl,

Plus, you do not understand at all what I am refering to when Sara's stone exhibits extreme fire in fire-unfriendly situations.

Live long,

I guess you didn't explain it very well then did ya?

 

[yssie]

my opinion the virtual facets I pointed out below and their twins are the virtual facets most likely to show fire across the most lighting conditions on an RB.

Why?

ETA: I assume from face-up (slight tilts from directly before your nose)?

 

[Karl_K]

Why?

ETA: I assume from face-up (slight tilts from directly before your nose)?

yellow arrow is a VF caused by the pavilion main, blue arrow is a VF caused by the lower half.
What causes the virtual facet between them and why would it disappear in a diamond with poor optical symmetry?

 

[yssie]

How am I doing with this..

As far as I can tell the outline of a pair of those "in-between" VFs (with obstructing arrowshaft VF in between) is that of the pavilion main after polishing the lower halves in one "section" of diamond (lgf-pavilion main-lgf)

In a stone w/ poor optical symmetry if the polishing of those lower half facets is skewed the mains aren't radially symmetric round the stone and arrows are malformed

So those "in-between" VFs are the primary refractions off those small portions of the pavilion mains that are able to return direct light without obstructing at close quarters

Assuming the mains are the recipients of the majority of light refracted through the crown from a variety of angles (and are well-angled for Tint.rfl.) then they must be able to output that dispersed light through that variety of angles, and those sliver "in-between" VFs that don't obstruct when faced with blockage of direct light are able to output dispersed light through those angles as well

...

 

[Karl_K]

Yssie, very close it is a reflection of the mains, lower half junction area.
In a non-symmetrical stone they may not exist because they don't line up.
It also makes sense that the angle tightness would make a difference also in lining them up.
From the earlier images the one on the right has some next to the mains but most of them are missing
The virtual diamond on the left has them.


Here is a image based on a real diamond scan, it is not just perfect virtual diamonds that have them.

 

[yssie]

and so does my non-H&A, though they're uneven - probably part photo part stone

 

[Paul-Antwerp]

Taking it one step further and it supports Paul's crispness theory my opinion the virtual facets I pointed out below and their twins are the virtual facets most likely to show fire across the most lighting conditions on an RB.

Karl,

This opinion of yours is not validated by real-life-observation. Can you even bring up a theory why these specific virtual facets are most likely to show fire?

They are indeed present in a very precisely cut diamond, and such diamonds indeed tend to show more fire, but where is the relationship between those specific virtual facets and fire?

Live long,

 

[Lula]

here you go

Leaving aside the discussion about the nature of fire and the wire frames and Karl's theory for a minute (because I am way out of my balliwick there) and returning for a moment to the side-by-side Marty-style graphics.

I may be way off here, but I found this diamond on my local Craigslist that seems to be a real life example of a diamond similar to the diamond on the right. It is a GIA good cut, good symmetry, good polish.

Link to report
http://www2.gia.edu/reportcheck/ind...tVerification&reportno=2115724566&weight=1.37

 

[ChunkyCushionLover]

Portree,

Interesting thread topic and great start by Karl and Paul Antwerp.
Here is some more information I hope will make things a little more clear.

1) The CA/PA and LGF Length combinations play a very large part in the appearances of the near tolk RB often times this overshadows the more suttle differences between near perfect optical HA (as defined by HRD or Brian in his paper) and perfect optical symmetry.
The last diamond you posted has a steeper pavillion angle (41.4) which contributes to its appearance significantly overshadowing its symmetry or lack thereof.

a) The LGF size changes the number and size of the virtual facets.
b) For any given size of diamond the greater the optical symmetry the greater the average virtual facet size.
c) Though we can quantify them there is no consensus on what virtual facet size is preferable. We know that historically the round brilliant evolved to smaller VFs and faster scintillation but there are still those who prefer the larger less frequent flashes.

A tolk with a 55% LGF has 25% less VFs than one with LGF of 80%(shown below) but they are much larger on average.

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.

2) Scintillation in the near tolk RB and in most other cuts is most prominant in areas that strongly return light to the viewer (e.g. ASET RED).

In the AGS research paper linked earlier by looking at their scintillation maps versus an ASET image one can see strong areas of scintillation that correspond to red areas in the ASET.


I would caution looking for a dramatic change in where the stone gathers light upon tilt (like ASET RED > BLUE shift) or lack thereof as any indication of strong or poor scintillation. While it is true that in a Tolk Round of fine make the main facets have been shown to gather light from 73 - 83 degrees (which falls in the border of Blue/Red in ASET 30) limited conclusions can be drawn from this.

Two facets can still be out of phase with each other but both still receive light from the 45 - 75 degree ASET30 red angular range or change their dependancies within this range upon tilt.

3) Due to the skill and yield loss constraints of cutting perfect hearts and arrows, it is still very rare for any brand or non brand to achieve the precision of perfect hearts and arrows (as seen by the HA images and defined by HRD or Brian's paper), yet fail in other areas like a bad CA/PA combination. I welcome any real actual cut diamond examples of stones with perfect hearts that don't also satisfy the other easier to achieve proportion sets.