GIA Diamond Cut Grading: Problems with Diamond Dock

[dhog]

I did not say that it was a c/z

read all of the post where you were refering
c/z''s as diamonds and better yet let me know
how many of those photo''s resemble each other

yes the photo is a true ACA but you were so quick
to castrate me again ,you would have seen that
on the following post

 

[Serg]

re:

You know what I don''t understand (and Garry, please don''t take this personally). Garry can post some shots of 2 cubic zirconia (not even diamonds and some out of focus), of which at this point we know nothing about (haven''t had a chance to read everything in this thread just yet in case he did post the stats), I offer photography in the best lighting conditions to depict brightness with some of the best equipment available for the job, on top of freely supplying the information on the stones and not once do you question, not one bit, about Garry''s photography or the diamond simulants in question.

In the other thread, and this one, I was getting hammered with ... (off the top of my head)

a. there was a .4 degree variance in the pavilion angles of one stone...
b. there might be strain in one stone
c. are the diamonds the same color
d. do both diamonds have equal optical symmetry ....
e. there might be a camera hood causing darkness on one stone and not the other...
f. perhaps the camera is too much in front of one diamond than the other...

I have not seen one question raised concerning the 2 faux stones Garry used to arrive at many of his conclusions.

Am I the only one here who finds this odd?

Garry ... let''s see some hard data on the cz stones you used. While I could contend the fact that they are not even diamonds, I give you the benefit of the doubt, however lets see the data please. I am curious.

Sorry I can''t stay longer ... gotta head out now. Not sure how soon I can return but as Arnie would say ... I''ll be back


Rhino,

You took two similar and very good diamonds and try to proof What DD GIA can easy show which diamond is better.
Garry took one good and one very bad CZ and try to show what DD GIA can not easy show which CZ is better.
Other words Garry try show MACRO phenomena, You try show MICRO phenomena.
For you task you should use much more strong conditions of experiment.
Demand for experiment depends from task.
BTW. Did you remember my unique comments of Garry article?( You mix me with Belle)

 

[strmrdr]

Jon when you get a chance start a new thread and lay out the pictures with captions cuz im as confused as John apears to be trying to keep them strait.
Please :}

 

[JohnQuixote]

Date: 3/20/2006 11:35:22 PM
Author: Rhino

To my knowledge GIA does run a full Sarin DiaMension on the stones they grade. While certain Sarin's do have a problem *seeing* painted girdles (recall our discussion on 'What a Scanner Sees') A Sarin Diamension, especially accompanied with a 3D model and it is quite easy to see painting or digging and to what degree it has been done. My personal goal is being able to detect how much and how each degree of this impacts face up appearance. This is why Sergey's, Mike Cowings comments on the 'clicks' interests me.

In short strmrdr, the reason GIA bans certain degrees of both painted and dug out girdles is because they found observation testing of humans can detect these differences with their eyes once painting and digging reach a certain threshold.

Peace,

I thought a lot today about how to communicate why judging brillianteering with a proportions scan is not sufficient. For fun, here are 2 broad comparisons:

(1) Artistry: Some of the world's greatest composers would receive poor marks at University for aspects of their works that, on paper, run contrary to certain prescribed rules. But when heard in the context of the performance (not looked at as numbers or pitches), they make perfect sense - and may even be considered masterpieces. It is the quality and effectiveness of the performance that matters.

Or

(2) Judgment: Finishing a diamond is like landing an airplane: You can suggest gear 'should' come down at X altitude, X amount of flaps, X thrust, etc... But what's appropriate for the situation depends on the weather, degree above/below sea level, wind and other variables. Each landing must be judged on it's own merits; what was appropriate and safe at the time. It is the end result that matters.

If the pilot NEEDS to put the gear down above or below the 'textbook' altitude - and it saves the plane - his actions should not be downgraded (unless he then ran it into the terminal).

This is why the diamond must be judged by the finished product.

To their credit, AGS understands this.

 

[strmrdr]

Date: 3/21/2006 3:08:27 AM
Author: dhog
I did not say that it was a c/z


read all of the post where you were refering

c/z''s as diamonds and better yet let me know

how many of those photo''s resemble each other


yes the photo is a true ACA but you were so quick

to castrate me again ,you would have seen that

on the following post

have no clue what your talking bout but ok.
I''m sorry if it seemed as if I was getting on your case.
Maybe when I re-read it when I''m awake it will look like I was Dunno
You may have got caught in the cross fire.
In any case I apologize.

 

[dhog]

Date: 3/21/2006 3:18:41 AM
Author: strmrdr

Date: 3/21/2006 3:08:27 AM

Author: dhog

I did not say that it was a c/z



read all of the post where you were refering


c/z''s as diamonds and better yet let me know


how many of those photo''s resemble each other



yes the photo is a true ACA but you were so quick


to castrate me again ,you would have seen that


on the following post

have no clue what your talking bout but ok.

I''m sorry if it seemed as if I was getting on your case.

Maybe when I re-read it when I''m awake it will look like I was Dunno

You may have got caught in the cross fire.

In any case I apologize.

ok I''LL throw you back in the sea
but remember its not about you or me or rhino or painted
girdles its about our childrens futures. think about going
fishin next time.

the beauty of catch and release

you live to fight another day cool

 

[strmrdr]

Date: 3/21/2006 3:16:46 AM
Author: JohnQuixote

Date: 3/20/2006 11:35:22 PM

Author: Rhino


To my knowledge GIA does run a full Sarin DiaMension on the stones they grade. While certain Sarin''s do have a problem *seeing* painted girdles (recall our discussion on ''What a Scanner Sees'') A Sarin Diamension, especially accompanied with a 3D model and it is quite easy to see painting or digging and to what degree it has been done. My personal goal is being able to detect how much and how each degree of this impacts face up appearance. This is why Sergey''s, Mike Cowings comments on the ''clicks'' interests me.


In short strmrdr, the reason GIA bans certain degrees of both painted and dug out girdles is because they found observation testing of humans can detect these differences with their eyes once painting and digging reach a certain threshold.



Peace,

I thought a lot today about how to communicate why judging brillianteering with a proportions scan is not sufficient. For fun, here are 2 broad comparisons:


(1) Artistry: Some of the world''s greatest composers would receive poor marks at University for aspects of their works that, on paper, run contrary to certain prescribed rules. But when heard in the context of the performance (not looked at as numbers or pitches), they make perfect sense - and may even be considered masterpieces. It is the quality and effectiveness of the performance that matters.


Or


(2) Judgment: Finishing a diamond is like landing an airplane: You can suggest gear ''should'' come down at X altitude, X amount of flaps, X thrust, etc... But what''s appropriate for the situation depends on the weather, degree above/below sea level, wind and other variables. Each landing must be judged on it''s own merits; what was appropriate and safe at the time. It is the end result that matters.


If the pilot NEEDS to put the gear down above or below the ''textbook'' altitude - and it saves the plane - his actions should not be downgraded (unless he then ran it into the terminal).

This is why the diamond must be judged by the finished product.


To their credit, AGS understands this.

well said John the bottom line is that a kicken diamond is a kicken diamond and there are several ways to get there.
I dont like the arbitrary cut off on the GIA system.

 

[JohnQuixote]

(3) Simple: A kicken diamond is a kicken diamond.

I like it.

(thanks btw)

 

[strmrdr]

John your quote of Jon showed me something I missed:

Jon said:

"In short strmrdr, the reason GIA bans certain degrees of both painted and dug out girdles is because they found observation testing of humans can detect these differences with their eyes once painting and digging reach a certain threshold. "

especially in scint, but is it really a bad thing if some consumers prefer it?
That's what keeps me from saying its a bad thing.
Its not my cup of tea but some consumers who have taken the time to become educated about diamonds love it and preferred it.
I like the AGS approach where if the diamond is an otherwise kicken performer the specific look of good type painted or dug girdles is allowed.
From there it is up to the educated consumer to accept or reject it.

I go back to my asscher studies in the larger sizes I dont care for the drop style (in small ones there is an advantage of showing a pattern better and they are growing on me in larger sizes but not past 1.5ct or so)
but the other day I showed my sister who has never seen an asscher the DC image lineup of the 3 types and she pointed to the drop asscher and said it was the kewlest diamond she has ever seen.
Then she saw RichardAlex's ring she said it was the most awesome ring she had ever seen.
Should I have told her no it wasn't that its technically inferior to the wide-step asscher in light return?
Should I tell those that love that pattern not to buy it even if its an awesome asscher and they love the pattern?
No, I point out that its a kicken drop style asscher and let them decide from there.
Same with painted girdles on rounds.

 

[strmrdr]

Date: 3/21/2006 3:39:45 AM
Author: JohnQuixote
(3) Simple: A kicken diamond is a kicken diamond.


I like it.


(thanks btw)

Welcome :}

 

[WinkHPD]

I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, that having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle.

What, if anything, am I missing here?

Wink

 

[Serg]

Date: 3/21/2006 7:19:15 AM
Author: Wink
I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, that having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle.

What, if anything, am I missing here?

Wink

re:I keep thinking that if our head shadow provides most of the contrast for a diamond

Wink,

I do not believe that head shadow gives the diamond so much of its sparkle in real light scheme.

I prefer to separate special visual phenomena( like arrows) from contrast( static and dynamic)

in Other words. Head shadow can do bad diamonds worse, but head shadow can not do good diamonds better( more sparkle) in real light scheme( Of course in exotic light scheme like GIA hemisphere Head can be positive)


May be I am wrong here, Need time to think. Interesting question.

 

[strmrdr]

Date: 3/21/2006 7:19:15 AM
Author: Wink
I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, that having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle.


What, if anything, am I missing here?


Wink

hmmmm Wink in the pictures of the Garry's CZ's it looks like to me the dark close confines of the DD are giving the cz a dark brackish look for the lighted facets to contrast with.
Iv noticed it in the other pictures of actual diamonds also the diamond look too gray.
That's why I would be interested in the walls covered with red paper to see what kind of environmental effect its having.
Something iv been considering but haven't had time to write up is that "head shadow" contrast in the real world may be secondary to environmental contrast.
If you look at the pictures Garry posted of the Lady looking at the diamond what in the picture is blocking more light her head or the huge seat cushion? Which will be reflected more?
Out in the open in sunlight yea the head may be the biggest source but if the diamond is reflecting the blue of the sky in that condition what effect is the relatively bright white ceiling having inside say a typical living room with side lamps?

 

[adamasgem]

Date: 3/21/2006 8:35:24 AM
Author: Serg

Date: 3/21/2006 7:19:15 AM
Author: Wink
I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, that having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle.

What, if anything, am I missing here?

Wink

re:I keep thinking that if our head shadow provides most of the contrast for a diamond

Wink,

I do not believe that head shadow gives the diamond so much of its sparkle in real light scheme.

I prefer to separate special visual phenomena( like arrows) from contrast( static and dynamic)

in Other words. Head shadow can do bad diamonds worse, but head shadow can not do good diamonds better( more sparkle) in real light scheme( Of course in exotic light scheme like GIA hemisphere Head can be positive)


May be I am wrong here, Need time to think. Interesting question.

Wink, the "vital contrast pattern" is provided by symmetry in cutting combined with head shadow.

The "sparkle", or what is alternatively termed scintilation or dynamic pattern breakup. I believe, is caused mainly by assymmetry/misalignments in cutting..

When I first looked at an EightStar under a microscope, (while visiting AGSL a long time ago), I was really surprised at the lack of "vital contract pattern" breakup as I moved the stone around, the contrast pattern seemed to "roll" (change position) rather than "breaking up", and I think I reffered to it then as "static", not what "people" would expect or are used to seeing. Again the opal analogy I often use, which appears consistent with the type of fire produced (rolling broadflash).

It is interesting to note that rolling broadflash is the most prized (and expensive) type of opal fire. I think that the cutters art which produces this type of phenomena is not recognised well enough..

A perfectly symmetric diamond is not going to have as much "sparkle", or small light/dark pattern breakup (dynamic contrast), but the symmetric stone will have more broadflash fire than one with more "sparkle (scintillation?)"

One of the problems I think, is that there is no distinction, right now, in some metrics with the "type" of fire. "Scintilation" is given in some measurement devices, neglecting broadflash aspects. I think they are mutually exclusive.

AGS, I think, from my interpretation of the ASET software fire diagrams, looks at the ability of the stone to provide fire that is more resolvable at distance, and may correlate more with broadflash, but I''m not sure. I believe they might be looking at this more closely.

"Scintilation" metrics I have seen, could be misleading, because of the mutual contradiction (broadflash/pinfire) and what is needed is a "typing" or measures of both, because you can''t "maximise" both at the same time. One goes up the other goes down. And I believe that people have to understand, that the more "scintilation" (light/dark), the less resolvable it is as you move away from the stone.

 

[belle]

Date: 3/21/2006 9:11:17 AM
Author: strmrdr

Date: 3/21/2006 7:19:15 AM
Author: Wink
I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, that having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle.


What, if anything, am I missing here?


Wink

hmmmm Wink in the pictures of the Garry''s CZ''s it looks like to me the dark close confines of the DD are giving the cz a dark brackish look for the lighted facets to contrast with.
Iv noticed it in the other pictures of actual diamonds also the diamond look too gray.
That''s why I would be interested in the walls covered with red paper to see what kind of environmental effect its having.
Something iv been considering but haven''t had time to write up is that ''head shadow'' contrast in the real world may be secondary to environmental contrast.
If you look at the pictures Garry posted of the Lady looking at the diamond what in the picture is blocking more light her head or the huge seat cushion? Which will be reflected more?
Out in the open in sunlight yea the head may be the biggest source but if the diamond is reflecting the blue of the sky in that condition what effect is the relatively bright white ceiling having inside say a typical living room with side lamps?

i''ve been called ''weird''

for daily trying to determine the effect environment has on the optics of diamonds, and am very curious as to what role dd would play in getting closer to this answer. lining the walls with different colored paper may help understand not only how closely the dd corresponds with ''real life'' conditions, but also the possible short comings of dd that were the original topic of this thread.

 

[belle]

marty...
very awesome pictures! that is by far the closest thing to what my eyes see in a well cut diamond under my very favorite light conditions. excellent.

 

[dhog]

Date: 3/21/2006 9:11:17 AM
Author: strmrdr

Date: 3/21/2006 7:19:15 AM

Author: Wink

I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, that having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle.



What, if anything, am I missing here?



Wink

hmmmm Wink in the pictures of the Garry''s CZ''s it looks like to me the dark close confines of the DD are giving the cz a dark brackish look for the lighted facets to contrast with.

Iv noticed it in the other pictures of actual diamonds also the diamond look too gray.

That''s why I would be interested in the walls covered with red paper to see what kind of environmental effect its having.

Something iv been considering but haven''t had time to write up is that ''head shadow'' contrast in the real world may be secondary to environmental contrast.

If you look at the pictures Garry posted of the Lady looking at the diamond what in the picture is blocking more light her head or the huge seat cushion? Which will be reflected more?

Out in the open in sunlight yea the head may be the biggest source but if the diamond is reflecting the blue of the sky in that condition what effect is the relatively bright white ceiling having inside say a typical living room with side lamps?

under these dd lighting condition it is a very
complex issue that has been under study for many
of years before us.

think of it like a jpeg file.

the bombardment of white light signals from the
photoreceptors will cause the brain to interpret
all dark signals as weak and replacing them with the stronger white light signals

 

[RockDoc]

To Serg.....

Is it possible to show scintillation affect through a "movie" type graphic on Diamond Calc.

Maybe also show the broadness of color with movement as well?

Scintillation is best viewed in a dark room using as low a light as possible and then adding movement of:

a ) the observer''s head
b) the movement of the stone
c) movement of the light source.

In the movement of the stone north to south movement up to maybe clicks of from 5-40 degrees.
Also East to West movement of the stone in individual "clicks" of from 5-40 degrees also.

Just a thought offering a "better" ''moustrap'' suggestion. Don''t know if this is possible, but perhaps something useful.

Rockdoc

 

[adamasgem]

Date: 3/21/2006 10:09:00 AM
Author: belle
marty...
very awesome pictures! that is by far the closest thing to what my eyes see in a well cut diamond under my very favorite light conditions. excellent.

Thanks Belle.. A lot of thought and engineering and trial and error went into it to make it happen, and more work and $$ required to bring it to market..

 

[Serg]

Date: 3/21/2006 10:39:32 AM
Author: RockDoc
To Serg.....

Is it possible to show scintillation affect through a ''movie'' type graphic on Diamond Calc.

Maybe also show the broadness of color with movement as well?

Scintillation is best viewed in a dark room using as low a light as possible and then adding movement of:

a ) the observer''s head
b) the movement of the stone
c) movement of the light source.

In the movement of the stone north to south movement up to maybe clicks of from 5-40 degrees.
Also East to West movement of the stone in individual ''clicks'' of from 5-40 degrees also.

Just a thought offering a ''better'' ''moustrap'' suggestion. Don''t know if this is possible, but perhaps something useful.

Rockdoc

re:Is it possible to show scintillation affect through a ''movie'' type graphic on Diamond Calc

Yes it is possible in current DC . But I do not like result. Current DC is not god for Fire and Scintillation.
We are changing calculation core in DC now. It it is reason of delay new version. New core should be much better for Fire and Scintillation tasks. In new DC we will use REAL light scheme( not synthetic like now)

 

[RockDoc]

Serg

Sounds very exciting. Can''t wait for the update.

Are you going to be able to go the AGS conclave in Orlando?

Let me know at my email, ( [email protected] ) if you need a ride to hotel from airport, or help in getting room etc.

Since you maybe are able to visit in my neck of the woods....I''ll be a good host for you.

Rockdoc

 

[JohnQuixote]

Date: 3/21/2006 11:15:10 AM
Author: Serg





re:Is it possible to show scintillation affect through a 'movie' type graphic on Diamond Calc

Yes it is possible in current DC . But I do not like result. Current DC is not god for Fire and Scintillation.


We are changing calculation core in DC now. It it is reason of delay new version. New core should be much better for Fire and Scintillation tasks. In new DC we will use REAL light scheme( not synthetic like now)

DC is remarkable already. I'm looking forward to seeing how 'real' it can be made. It imagine is a tremendous challenge to represent the 3D nature of fire and scint and their dynamics in 2D.

 

[Serg]

Date: 3/21/2006 11:24:29 AM
Author: RockDoc
Serg

Sounds very exciting. Can''t wait for the update.

Are you going to be able to go the AGS conclave in Orlando?

Let me know at my email, ( [email protected] ) if you need a ride to hotel from airport, or help in getting room etc.

Since you maybe are able to visit in my neck of the woods....I''ll be a good host for you.

Rockdoc

Thanks. I booked hotel.
re:Since you maybe are able to visit in my neck of the woods....

Sorry, can not translate it. Slang is too difficult to me.

re:Are you going to be able to go the AGS conclave in Orlando?

Should receive answer in Friday

 

[Serg]

re: It imagine is a tremendous challenge to represent the 3D nature of fire and scint and their dynamics in 2D.

I think 2D or 3D is not very important for quality of fire and Scintillation.( Just important for quantity of flashes). Moving is much more important( and adequate light scheme)
If it will necessary we can support stereo mode.( But you need special glasses, videocard and CRT monitor. It is not user friendly technology

)

 

[Shay37]

Date: 3/20/2006 11:15:59 AM
Author: Rhino

Date: 3/20/2006 9:02:47 AM
Author: Shay37

Date: 3/20/2006 3:56:03 AM
Author: Rhino
This picture was also taken outside in natural daylight. After talking with Pete he mentioned that the pavilions should be covered since the PGS software didn''t account for light entering through the pavilion. Based on my experience with backgrounds and diamond observation I find neautral colors work best except if your mounting a diamond in a bezel mounting ... then a black background would be more appropriate.

strm, dhog, shay... can anyone identify which is which? 2 varying views of the stone yet there are commonalities in each shot. Pavilion covered or not.

Just going to take a shot in the dark here. I hope I guess right, but after studying the photo, I''m going to say painted on the left.

shay

Shay ... your eyes deceive you not. It is your unbiased opinion that counts most to me dear and thank you for answering.

Awww, thanks. It was easy after having two specimens in my own hands. I call it the tips, spokes, and arrows test.

After viewing side by side I picked up on some differences that were subtle and slight, but they do help in the identification factor. In lighting most favorable to produce spectral color from the arrows, the whole arrow of the painted lit up. The non-painted did a tip and spoke thing.

Simply put, the tip of the arrow would pop, and the arrow shaft would not light up all at once. It would have a sliver light up that made it look like a bicycle spoke reflecting light or color. Look for the tips and spoke in the pic on the right. Diamond on the left has a bigger flash of return.

Saying all that to say this: It''s like Christmas tree lights. Some people prefer the little ones, and some people prefer the bigger ones. They are both pretty to look at when the tree is decked out.

shay

 

[RockDoc]

Date: 3/21/2006 11:34:44 AM
Author: Serg

Date: 3/21/2006 11:24:29 AM
Author: RockDoc
Serg

Sounds very exciting. Can''t wait for the update.

Are you going to be able to go the AGS conclave in Orlando?

Let me know at my email, ( [email protected] ) if you need a ride to hotel from airport, or help in getting room etc.

Since you maybe are able to visit in my neck of the woods....I''ll be a good host for you.

Rockdoc

Thanks. I booked hotel.
re:Since you maybe are able to visit in my neck of the woods....

Sorry, can not translate it. Slang is too difficult to me.

re:Are you going to be able to go the AGS conclave in Orlando?

Should receive answer in Friday

"Neck of the woods" means my area, where I live.

Getting from airport to hotel can be a challenge in Orlando. Orlando is difficult to drive in. Many of the roads are confusing, and difficult to navigate in, particularly if you aren''t familiar with the area.

Since I live local to Orlando I know my way around. So I''ll volunteer to be as helpful as I can be.

Rockdoc

 

[RockDoc]

I thought a lot today about how to communicate why judging brillianteering with a proportions scan is not sufficient. For fun, here are 2 broad comparisons:

(1) Artistry: Some of the world''s greatest composers would receive poor marks at University for aspects of their works that, on paper, run contrary to certain prescribed rules. But when heard in the context of the performance (not looked at as numbers or pitches), they make perfect sense - and may even be considered masterpieces. It is the quality and effectiveness of the performance that matters.

Or

(2) Judgment: Finishing a diamond is like landing an airplane: You can suggest gear ''should'' come down at X altitude, X amount of flaps, X thrust, etc... But what''s appropriate for the situation depends on the weather, degree above/below sea level, wind and other variables. Each landing must be judged on it''s own merits; what was appropriate and safe at the time. It is the end result that matters.

If the pilot NEEDS to put the gear down above or below the ''textbook'' altitude - and it saves the plane - his actions should not be downgraded (unless he then ran it into the terminal).

This is why the diamond must be judged by the finished product.

To their credit, AGS understands this.


John


Hey John.

Landing a plane has a lot more complexities.

But you''ve touched on just a few of the requirements.

To add some..... to the list.


Weight and balance.

Approach speed is the requirement for when to put the gear down.

Attitude is very critical... ( how high you raise the nose on approach and touch down )

Crosswind component ( whether or not you have to lower one of the wings to compensate for a cross wind that might keep the plane from drifting off the center line.

Power on of power off landing.

Visual conditions on approach... ( if you can see the runway at a specific altitude)

Verifying other traffic in the airports landing pattern, and entering the pattern correctly- especially on approach if IFR.

(All this is meant to tease you a bit) .... A lot of this could be compared to speed of cutting wheel, type of slurry/grit, yaw angle, placement on wheel in relation to graining, strain etc.

Rockdoc (who is a pilot)

 

[michaelgem]

Thoughts on the role of contrast in illumination to optical performance in a diamond

There are so many interesting thoughts, observations, and sub-threads within this thread that it is difficult to address them all or do them justice. I was especially attracted to this dialog between Wink and Sergey:

I keep thinking that if our head shadow provides most of the contrast for a diamond when it is worn and observed, then having the light between us and the diamond as it is in a Diamond Dock removes most of the effect of the head shadow, thus removing the vital contrast pattern that gives the diamond so much of its sparkle. Wink

I do not believe that head shadow gives the diamond so much of its sparkle in real light scheme. I prefer to separate special visual phenomena (like arrows) from contrast( static and dynamic) Sergey

In other words, head shadow can make bad diamonds worse, but head shadow can not make good diamonds better( more sparkle) in real light scheme ( Of course in exotic light scheme like GIA hemisphere Head can be positive) Sergey

I agree with Sergey''s thinking. It accords with a lot of what I try to get across about why the best ideal cut diamonds are preferred and seen as more beautiful.

Contrast in the illumination at "high angles" that is close, but not too close to the viewer''s line-of-sight is important to contrast brilliance (static contrast), scintillation (dynamic contrast), and fire as well. Ideal cuts make positive use of this contrast while poor cuts are hurt by it.

In my open sky illumination example, the contrast from my head obstruction provides most of the high angle contrast that would otherwise be absent. Compare these two diamond photographs. Both are under diffuse illumination, but the one from the open sky illumination has high-angle contrast from my silhouette. As these photos illustrate, without contrast in illumination, a diamond lacks contrast brilliance, scintillation and fire.

So Wink,

While contrast is essential to diamond beauty, it does not have to come from head obstruction. It is present in typical illumination for other reasons as well. The always present viewer''s head does guarantee at least that mechanism for contrast.

Contrast from head obstruction is not necessary if contrast is already present at high angles as it is in most asymmetric, high contrast lighting conditions including use of a desk lamp or Diamond Dock.

Michael Cowing

www.acagemlab.com

 

[WinkHPD]

I want the one in the middle. I do not like the head shaped one on the left, it is too dark, and the one on the right seems a little lifeless.

Yup, I definitely like the one in the middle...

Wink

 

[dhog]

if the inside of the dd is light gray and you had
a white light reflecting would the background be gray
or white.

what would happen if I shined a light through
the back of a leaking stone as in the one used
in these threads.

below is a simulated graphic only and a little overdone.

to demonstrate this take a piece of white paper
make a light gray mark on it maybe 1/2 inch x 1 inch

then take it outside in the sun at your back
hold the paper at arms length and slowly change
the angle of the sun hitting the paper

gone fishin