Obstruction

[John P]

Date: 11/19/2009 3:02:44 PM
Author: Rockdiamond

Very informative post John!
Hearing a reasonable explanation of what 'Obstruction' refers to is extremely useful to this conversation. Thank you very much for adding it!

You're welcome David.

It seems to me that the term the term, or concept of 'Obstruction' is used frequently here on PS to create doubt about a stone's beauty.

It should not be unless the diamond has a shallow enough configuration that the obstruction interferes with visual appeal.

There seems to be a lot of holes in the entire theory.
At the root of my problem with how this translates into reality is this statement: 'at any angle the viewers head will block some light getting to the diamond'
You would not need to be a member of the Fantastic Four to look at a diamond in a position that your head blocks no light.

I suggest you are thinking in one direction only. Think hemispherically: Regardless of where the main light source is a viewer's face will be reflected in the diamond. That is obstruction. Think of it this way; when you look directly into a mirror it does not matter where the light source is, you will still see your reflection... When you look at a diamond it does not matter where the light source is, your presence still creates a reflection.

Both major labs and prominent researchers (beginning with the legendary Bruce Harding) acknowledge that while the world is generally lit from above one must account for the presence of the viewer in the way a diamond gathers light, regardless of location.

Same question about looking at a diamond under a grading lamp.
I'm behind the diamond which is directly under the lamp.
How can my head obscure an important amount of light- enough so that it would have any effect against the bright diamond light which is 3 inches directly above the diamond?

Try again. You will find the diamond is not completely white with light; the upper girdles and bezels go dark. This is because the obstruction is now occuring from around the sides, not from above. Even if you illuminate the walls of the room your arms or the holder will still cause some blockage. And if you tilt it under the lamp enough to see it face-on the patterns will shift because your face is now partially contributing.

Taken one step further, I know that a deeply cut diamond will show a dark center if I'm looking at it under a diamond light- where the head can not obstruct any light. Therefore 'head obstruction' is not causing the center of the deep diamond to look dark.

That's leakage.

There would seem to be so few positions of light and diamond that would allow the head to obscure significant light.

The theory that the head's shadow will adversely affect one diamond more than another, based on the crown and pavilion angle might make academic sense, but it would seem to be hard to correlate this to 'real world' examples when people look at diamonds. This is partially because of how many different lighting situations we are all exposed to all day long.

It all comes down to the configurations being compared.

If you want to compare extremes which are notable through a broad panorama of illumination scenarios try comparing a Tolk H&A round (with sharp, even contrast patterns) to a low-crowned princess cut with 4-5 chevrons and a table in the high 70s: You will see a dramatic difference in the way obstruction works.

 

[rockabee]

Date: 11/19/2009 3:43:57 PM
Author: John Pollard

Date: 11/19/2009 3:32:17 PM
Author: rockabee

i am very new to all of this, but it seems to me that most real world views of a diamond are at a tilt. sure, sometimes a person looks directly at it so that they are facing the table at a bird''s eye view. but even in those cases, it is not clear that primary light sources are directly obstructed. anyways, none of this is a revelation. but what are the implications for the importance of viewing light return at a tilt and what are the ramifications for instruments like the ideal scope and aset, which really measure the view of light return when viewed directly above the center of the table?

should there be a tilted version of an aset/IS made to complement the existing ones so that we can have a sense of light performance at other common viewing angles? i think AGS measures performance on their DQD with many angles of viewing and DQR with a bird''s eye and a 45 deg angle (don''t quote me on that). are we overly obsessing on every nook and cranny of IS/aset images when in fact, that view may represent only a limited % of total real life viewing situations?

The AGS Platinum (DQD) metric models the diamond in 3D through a 45-degree range of tilt, in 1 degree increments, at both 30 and 40 degrees of obstruction to arrive at its deductions/values. The Gold uses static 2D measurements. They do incorporate predictive tilt to some degree but it does not take the specific diamond into account.

In the trade this has been discussed ad nauseum. The consensus from the major labs and researchers is that analysis face-up is the logical standard approach. It was the basis for the Firescope, Gilbertson, Ideal-Scope and ASET. It is how GIA conducted their observational research.

The most advanced studies are now accounting for tilt as well, which has allowed more in-depth assessment approaches and improved handshaking between diamond design/modeling and production.

john, what concerns me is that most of us do not have/buy stones that have AGS plat certs. we see a GIA cert, plug the dimensions into HCA and if it looks good on that, ask for ASET/IS image. i just wonder if there was an ASET/IS viewer with say a 30 and 45 tilt to it, how different the image of certain cuts may look. anyways, i''m not trying to rehash a much discussed topic so i''ll just leave it at that. i guess at the end of the day, bottom line is, you can get all the stats and images, but just see it in person and under various lighting conditions and base your decision on that.

 

[John P]

Date: 11/19/2009 3:51:51 PM
Author: Rockdiamond

Date: 11/19/2009 3:28:36 PM
Author: Karl_K
but if it stays that way to far out beyond the point that the patterns is visible it just looks dark.
This is said to have obstruction issues.
This point is general considered to be 1/2 arm length for most people or about 15 inches.

Karl- actual photos that show the darkness you created on this simulation of a diamond are what I've been asking to see.
Your gnerated image shows it clearly. If any of the actual diamonds being knocked showed such a clear dark pattern, than it would be easy to illustrate a problem with a camera.

John- I'd be very interested in your opinion of all this.
Aren't there many positions where the head can not obstruct light?

Only if your head is in the other room.

Even if you cover the diamond with an illuminated globe and cut a small peephole in the top - when your eye is looking through the peephole the diamond reflects your eye. It's what diamonds "do."

 

[stone-cold11]

Date: 11/19/2009 4:03:21 PM
Author: Rockdiamond
Stone, here''swhat you''re referring to as an explaination:

Some diamonds could be bright only if your head is Bright(Bright light source, I mean). You can use a lot of lights in different directions but you will see just yourself in these diamonds. most known example is 90 degree prism. but you can achieve same result by diamonds too. See example. most known example for diamond traders is Bow-tie Sergey Sivovolenko

CEO OctoNus

I have tremendous respect for Sergey- yet this post does not explain ''Obstruction''as it''s commonly used on PS.

I did not say obstruction issue, I am saying about the optics. Look at the ray diagram. The stone with obstruction issue is cut such that light that it reflects back to the observer mainly comes from the direction of the observer. Tilt the light source, most of the light reflected is not going to be seen by the observer, so it is still going to be less bright.

 

[stone-cold11]

Date: 11/19/2009 4:07:23 PM
Author: rockabee
john, what concerns me is that most of us do not have/buy stones that have AGS plat certs. we see a GIA cert, plug the dimensions into HCA and if it looks good on that, ask for ASET/IS image. i just wonder if there was an ASET/IS viewer with say a 30 and 45 tilt to it, how different the image of certain cuts may look. anyways, i'm not trying to rehash a much discussed topic so i'll just leave it at that. i guess at the end of the day, bottom line is, you can get all the stats and images, but just see it in person and under various lighting conditions and base your decision on that.

ASET/IS simulates a viewer's head located at about 14 inch from the stone with the contrast (black for IS/blue for ASET).

 

[Karl_K]

Date: 11/19/2009 3:51:51 PM
Author: Rockdiamond

Date: 11/19/2009 3:28:36 PM

Author: Karl_K

but if it stays that way to far out beyond the point that the patterns is visible it just looks dark.

This is said to have obstruction issues.

This point is general considered to be 1/2 arm length for most people or about 15 inches.

Karl- actual photos that show the darkness you created on this simulation of a diamond are what I''ve been asking to see.

Your gnerated image shows it clearly. If any of the actual diamonds being knocked showed such a clear dark pattern, than it would be easy to illustrate a problem with a camera.


John- I''d be very interested in your opinion of all this.

Aren''t there many positions where the head can not obstruct light?

pictures of diamonds almost always have to much head shadow compared to a person viewing it.
For that reason pictures are not a good way to determine if it has issues.
Since the crown/pavilion angles that it can be an issue with are known unless it will clearly be in the obstructed zone like the one under discussion here the best advise is have it checked by the vendor.
Who hopefully but not always will know what to look for.
Some combinations will have issues it is physics some might or might not depending on the actual diamonds angles.

 

[Lorelei]

Date: 11/19/2009 4:10:05 PM
Author: John Pollard

Date: 11/19/2009 3:51:51 PM
Author: Rockdiamond

Date: 11/19/2009 3:28:36 PM
Author: Karl_K
but if it stays that way to far out beyond the point that the patterns is visible it just looks dark.
This is said to have obstruction issues.
This point is general considered to be 1/2 arm length for most people or about 15 inches.

Karl- actual photos that show the darkness you created on this simulation of a diamond are what I''ve been asking to see.
Your gnerated image shows it clearly. If any of the actual diamonds being knocked showed such a clear dark pattern, than it would be easy to illustrate a problem with a camera.

John- I''d be very interested in your opinion of all this.
Aren''t there many positions where the head can not obstruct light?

Only if your head is in the other room.

Even if you cover the diamond with an illuminated globe and cut a small peephole in the top - when your eye is looking through the peephole the diamond reflects your eye. It''s what diamonds ''do.''

Thanks John, choking on a hot drink with laughter is most unpleasant!

 

[Serg]

Date: 11/19/2009 4:03:21 PM
Author: Rockdiamond
Stone, here''swhat you''re referring to as an explaination:

Some diamonds could be bright only if your head is Bright(Bright light source, I mean). You can use a lot of lights in different directions but you will see just yourself in these diamonds. most known example is 90 degree prism. but you can achieve same result by diamonds too. See example. most known example for diamond traders is Bow-tie Sergey Sivovolenko

CEO OctoNus

I have tremendous respect for Sergey- yet this post does not explain ''Obstruction''as it''s commonly used on PS.

RD, it is same. but I tried explain you the Reason, when Ps''s usually show you results( of such reason)

Take Karl example with black pavilion facets under table. Black facets are result of head obscuration . But reason is what you Can not find position for light source when these facets become bright in "in Karl viewer conditions". there is big difference between two statements "Facet is black because Head block light " and "There is not position for light sources when this facet could be bright" . Do you see this difference now?

 

[stone-cold11]

Date: 11/19/2009 4:10:05 PM
Author: John Pollard
Only if your head is in the other room.

Even if you cover the diamond with an illuminated globe and cut a small peephole in the top - when your eye is looking through the peephole the diamond reflects your eye. It''s what diamonds ''do.''

Or Superman''s laser eyes? :p

 

[Rockdiamond]

Date: 11/19/2009 4:10:05 PM
Author: John Pollard

Date: 11/19/2009 3:51:51 PM
Author: Rockdiamond

Date: 11/19/2009 3:28:36 PM
Author: Karl_K
but if it stays that way to far out beyond the point that the patterns is visible it just looks dark.
This is said to have obstruction issues.
This point is general considered to be 1/2 arm length for most people or about 15 inches.

Karl- actual photos that show the darkness you created on this simulation of a diamond are what I''ve been asking to see.
Your gnerated image shows it clearly. If any of the actual diamonds being knocked showed such a clear dark pattern, than it would be easy to illustrate a problem with a camera.

John- I''d be very interested in your opinion of all this.
Aren''t there many positions where the head can not obstruct light?

Only if your head is in the other room.

Even if you cover the diamond with an illuminated globe and cut a small peephole in the top - when your eye is looking through the peephole the diamond reflects your eye. It''s what diamonds ''do.''

John, in your own words, the diamond in your scenario reflects the light back to the eye- which is different from obstructing light.
IN any event, looking through the illuminated globe does not have anything in common with the sun shining on a diamond when your head is not obstructing the light hitting the diamond.

Sergey- I so much appreciate your input- I believe it''s probably a language issue, but I did not understand your statement.


PS- how do you know my head is not in the other room

 

[John P]

Date: 11/19/2009 5:30:36 PM
Author: Rockdiamond

John, in your own words, the diamond in your scenario reflects the light back to the eye- which is different from obstructing light.

David. Unless you have SC's Superman-laser-eye your eye is dark. The diamond reflects back the darkness of your eye. That is obstruction. Perhaps read my mirror comparison again.

PS- how do you know my head is not in the other room

Unless you 'get' this soon I'm a-thinking it is!

(rim shot)

 

[Rockdiamond]

So the term "Head Obstruction" actually refers to reflection?
Doesn't the diamond reflect back other, lighter parts of our heads?
All due respect but in either of our cases, there's plenty of forehead to reflect back- a whole lot more than a person's pupil. ( and a whole lot more of my forehead as compared to 20 years ago)

I very much appreciate the opportunity to discuss this John.
Maybe the term "Obstruction" being used to describe a reflection is the confusing part.
Wouldn't you think that "pupil reflection" better describes the effect you're talking about?


PS- Actually I have green eyes big boy ( Add second rim shot)

 

[stone-cold11]

Date: 11/19/2009 6:10:01 PM
Author: Rockdiamond
So the term ''Head Obstruction'' actually refers to reflection?

Doesn''t the diamond reflect back other, lighter parts of our heads?

All due respect but in either of our cases, there''s plenty of forehead to reflect back- a whole lot more than a person''s pupil. ( and a whole lot more of my forehead as compared to 20 years ago)

I very much appreciate the opportunity to discuss this John.

Maybe the term ''Obstruction'' being used to describe a reflection is the confusing part.

Wouldn''t you think that ''pupil reflection'' better describes the effect you''re talking about?

PS- Actually I have green eyes big boy ( Add second rim shot)

And what kind of light is that? It is not longer the full spectrum so the light you see will be colored even if your face is light color.

 

[Garry H (Cut Nut)]

Date: 11/17/2009 5:25:24 PM
Author: FB.
Yes, I''ve seen Garry''s obstruction video.

But most talk of obstruction is referring to perfect face-on views of the diamond. But diamonds are rarely viewed face-on at 6-12 inches, when being worn, particularly to casual observers.

I''m curious how a badly obstructed stone would perform in a variety of normal environments, when illuminated by various types of light sources and viewed from a variety of angles.


In this example, this stone would be a pendant, so the minimum viewing distance would be about 2ft and the viewing angle could be as much as 30 degrees either side of straight-ahead.


Basically, if the viewing angle and lighting conditions change, is the stone always going to have serious problems no matter what? Is obstruction always going to starve it of enough light to sparkle?

FB here is a shallow stone where the observer will always see his own head in the stars

 

[Garry H (Cut Nut)]

And here is the stone tilted - with the dark zone window open - remember 1 is good.

 

[Garry H (Cut Nut)]

And here is a diamond with a extremely deep 45 degree 50% pavilion which also returns the light back to the viewers head in many zones.

 

[Garry H (Cut Nut)]

and straight on with Cut Quailty data

 

[Garry H (Cut Nut)]

David here is what Jess would see when she looked at this diamond. (Jess is having a baby soon - we hope she is doing well - she worked for me - and has very fair skin and blonde hair).

 

[Karl_K]

excellent Garry.

If someone wants to see obstruction in their RB diamond clearly put on a red ski mask and a red shirt.
bring the diamond closer and closer to your face you will see red obstruction under the table.
Now move it further away until the red disappears under the table.
That is the obstruction zone for your diamond.
Now view the diamond at full arm length as you move the diamond around you will see flashes of red but you should not see large bright red zones under the table if the diamond is well cut.
Most well cut diamonds the obstruction zone will end before 15 inches depending on the crown/pavilion angle.

 

[Karl_K]

Date: 11/19/2009 6:10:01 PM
Author: Rockdiamond


So the term ''Head Obstruction'' actually refers to reflection?

Doesn''t the diamond reflect back other, lighter parts of our heads?

All due respect but in either of our cases, there''s plenty of forehead to reflect back- a whole lot more than a person''s pupil. ( and a whole lot more of my forehead as compared to 20 years ago)


I very much appreciate the opportunity to discuss this John.

Maybe the term ''Obstruction'' being used to describe a reflection is the confusing part.

Wouldn''t you think that ''pupil reflection'' better describes the effect you''re talking about?



PS- Actually I have green eyes big boy ( Add second rim shot)

Look at a light across the room, now move you hand in between your eyes and the light.
Your hand is now obstructing the light from reaching your eyes.
In the same way head shadow obstructs the light reaching the diamond.
Obstruction is the proper term and is from the diamonds perspective.

 

[Lorelei]

Guys, this is a great thread!

 

[outatouch0]

Date: 11/20/2009 5:24:16 AM
Author: Lorelei
Guys, this is a great thread!

I agree, I have learned a lot about something I previously did not understand.

Nice to see that most of it was kept respectful.

 

[Rockdiamond]

Date: 11/20/2009 1:36:14 AM
Author: Karl_K

Date: 11/19/2009 6:10:01 PM
Author: Rockdiamond


So the term ''Head Obstruction'' actually refers to reflection?

Doesn''t the diamond reflect back other, lighter parts of our heads?

All due respect but in either of our cases, there''s plenty of forehead to reflect back- a whole lot more than a person''s pupil. ( and a whole lot more of my forehead as compared to 20 years ago)


I very much appreciate the opportunity to discuss this John.

Maybe the term ''Obstruction'' being used to describe a reflection is the confusing part.

Wouldn''t you think that ''pupil reflection'' better describes the effect you''re talking about?



PS- Actually I have green eyes big boy ( Add second rim shot)

Look at a light across the room, now move you hand in between your eyes and the light.
Your hand is now obstructing the light from reaching your eyes.
In the same way head shadow obstructs the light reaching the diamond.
Obstruction is the proper term and is from the diamonds perspective.

Karl, thanks for the demonstration.
When I do it, unless I put my hand directly over my eye, i can still see the light clearly.
In fact, I''d have to cover both eyes to completely obstruct the light.

Garry- congratulations and best wishes to Jess!!!

Thank you as well for posting the simulated diamonds in the graphs.
Do you see many diamonds that actually look like that in real life?
I don''t.
I''ve asked for photos showing such dramatic effects- none of the photos we''ve seen- even those that did show a dark center- looked anywhere near the simulated diamonds.

It seems to me that the issue of "Head obstruction" is not a condition that should concern diamond shoppers considering the wide variety of lighting conditions, and viewing angles.

A stone with a dark center- no matter how it''s caused, is likely not going to please a lot of shoppers. But this is the type of defect which is easily recognized without any training or special tools at all.

 

[stone-cold11]

Date: 11/20/2009 1:11:40 PM
Author: Rockdiamond
Karl, thanks for the demonstration.

When I do it, unless I put my hand directly over my eye, i can still see the light clearly.
In fact, I'd have to cover both eyes to completely obstruct the light.

Garry- congratulations and best wishes to Jess!!!
Thank you as well for posting the simulated diamonds in the graphs.

Do you see many diamonds that actually look like that in real life?
I don't.
I've asked for photos showing such dramatic effects- none of the photos we've seen- even those that did show a dark center- looked anywhere near the simulated diamonds.
It seems to me that the issue of 'Head obstruction' is not a condition that should concern diamond shoppers considering the wide variety of lighting conditions, and viewing angles.

A stone with a dark center- no matter how it's caused, is likely not going to please a lot of shoppers. But this is the type of defect which is easily recognized without any training or special tools at all.

That's is your opinion.

Then let the shopper knows what to look for, look at the stone itself and let him or her decide for herself. If he or she didn't own a diamond before or seen a lot of diamonds for comparison, the jeweler can just pass it off as 'Oh, all diamonds will have that effect.'

 

[Karl_K]

Date: 11/20/2009 1:11:40 PM
Author: Rockdiamond
Karl, thanks for the demonstration.

When I do it, unless I put my hand directly over my eye, i can still see the light clearly.

In fact, I''d have to cover both eyes to completely obstruct the light.


Garry- congratulations and best wishes to Jess!!!


Thank you as well for posting the simulated diamonds in the graphs.

Do you see many diamonds that actually look like that in real life?

I don''t.

I''ve asked for photos showing such dramatic effects- none of the photos we''ve seen- even those that did show a dark center- looked anywhere near the simulated diamonds.


It seems to me that the issue of ''Head obstruction'' is not a condition that should concern diamond shoppers considering the wide variety of lighting conditions, and viewing angles.


A stone with a dark center- no matter how it''s caused, is likely not going to please a lot of shoppers. But this is the type of defect which is easily recognized without any training or special tools at all.

Now your just being silly.
Anyone can obstruct a light with their hand.
But since that seems to hard for you use a 2x4.

Just because you don''t want to acknowledge it doesn''t mean it don''t exist.
Just keep on ignoring anything that don''t fit your world view.

 

[Rockdiamond]

Stone, that is exactly my point.
We can have 20 experts sitting around discussing light paths and tilt, but shoppers need to know what to look for!

Have you seen a lot of stones that look like the pictures of simulated diamonds in Garry''s posts?


Regardless, this is not brain surgery, and I can honestly say that the entire concept of "Head Obstruction" was never made clear in these discussions.

I do not, believe that shoppers need be concerned about it, and apparently others agree.

One of the first things in John''s explanations was

"Obstruction" aka "Head Shadow" (Bruce Harding) or "Obscuration" (AGS) is not bad. In fact without it a diamond with great light return would appear like a headlight.
[\quote]

Therefore, when a consumer comes to PS to ask about a stone, and is warned that by others that "there may be obstruction issues"- it may very well be a false warning. Who does that help?
If there is an actual issue, we need to be able to both explain the concept clearly, and show photos of what to look for.

 

[stone-cold11]

Date: 11/20/2009 1:33:20 PM
Author: Rockdiamond
Stone, that is exactly my point.

We can have 20 experts sitting around discussing light paths and tilt, but shoppers need to know what to look for!

Have you seen a lot of stones that look like the pictures of simulated diamonds in Garry's posts?

Regardless, this is not brain surgery, and I can honestly say that the entire concept of 'Head Obstruction' was never made clear in these discussions.

I do not, believe that shoppers need be concerned about it, and apparently others agree.

One of the first things in John's explanations was

'Obstruction' aka 'Head Shadow' (Bruce Harding) or 'Obscuration' (AGS) is not bad. In fact without it a diamond with great light return would appear like a headlight.

Therefore, when a consumer comes to PS to ask about a stone, and is warned that by others that 'there may be obstruction issues'- it may very well be a false warning. Who does that help?

If there is an actual issue, we need to be able to both explain the concept clearly, and show photos of what to look for.

You still have no idea what John is talking about it that sentence you quoted do you?

Who does that help? Help that consumers make an informed decision that's what.

 

[Rockdiamond]

Date: 11/20/2009 1:25:28 PM
Author: Karl_K

Date: 11/20/2009 1:11:40 PM
Author: Rockdiamond
Karl, thanks for the demonstration.

When I do it, unless I put my hand directly over my eye, i can still see the light clearly.

In fact, I''d have to cover both eyes to completely obstruct the light.


Garry- congratulations and best wishes to Jess!!!


Thank you as well for posting the simulated diamonds in the graphs.

Do you see many diamonds that actually look like that in real life?

I don''t.

I''ve asked for photos showing such dramatic effects- none of the photos we''ve seen- even those that did show a dark center- looked anywhere near the simulated diamonds.


It seems to me that the issue of ''Head obstruction'' is not a condition that should concern diamond shoppers considering the wide variety of lighting conditions, and viewing angles.


A stone with a dark center- no matter how it''s caused, is likely not going to please a lot of shoppers. But this is the type of defect which is easily recognized without any training or special tools at all.

Now your just being silly.
Anyone can obstruct a light with their hand.
But since that seems to hard for you use a 2x4.

Just because you don''t want to acknowledge it doesn''t mean it don''t exist.
Just keep on ignoring anything that don''t fit your world view.

I like it that "silly" is a fun word.
Karl, it is silly to state that one''s hand will obscure the light to a meaningful degree. We have fluorescent ceiling lighting here. If I extend my arm fully, I can just about cover the light with my hand, but guess what? The room is still lit, no matter how hard I try to "obscure" the light.
It''s like taking one finger and covering the sun. That simply ain''t gonna make it dark.
You silly silly man!

 

[FB.]

Thanks to all who replied. There''s some very good information in the postings. This thread will become very useful for people running searches in the future.

 

[FB.]

Having been reading the comments above and doing some searches about obstruction, how would the following minor adjustments affect the performance?

Reduce table size to 53% (to reduce the area of the central part of the stone which is dark)
Increase lower halves to 80% (to reduce the width of the black "arrow shafts" that cause the dark reflection under the table)
Increase pavilion angle to 40.0' (to reduce head-obstruction reflection)

Therefore, the stone becomes:

Table: 53%
Crown angle: 38.5'
Star: 50%
Pavilion angle: 40.0'
Lower half: 80%
Total depth: about 64% (slight extra depth due to smaller table meaning a higher crown if the original angle is retained)

Does that adjustment make a significant reduction in the obstruction effect? Have I learned something? Am I heading in the right direction?