Round Table: Best light conditions for Diamond Subjective performance comparison

[strmrdr]

We haven't done one of these in a while.

To get the conversation started.
My opinion there isn't one lighting condition that covers all aspects of diamond performance.
Trying to reduce it to one will lead to false results.

However there should be a few basic rules.
1: no back lighting
2: realistic environment behind the diamond.
3: realistic head shadow/obstruction


Discussion is open.

 

[Moh 10]

I know it's controversial, but what about the GIA Diamond Dock?

At least it is a currently-available single standard from a recognized authority that everyone could get.

Even if it is not perfect having one standard that everyone uses is a huge improvement over what we have today.

 

[strmrdr]

Date: 5/18/2009 12:03:17 PM
Author: Moh 10
I know some pros don''t like it but what about the GIA Diamond Dock?


At least it is a currently-available single standard from a recognized authority that everyone could get.


Even if it is not perfect having one standard that everyone uses is a huge improvement over what we have today.

The DD was a nice try but made to many compromises in my opinion.
The first is the use of led lighting which will never be mainstream in that form because it hurts peoples eyes over a long day being in it.
The second is the angle of the lighting to the diamond to the viewer.
I think even with its flaws it can be useful when the results are interpreted carefully.
Hopefully this will not turn into another DD rant thread or we will achieve nothing.

 

[Moh 10]

Strm, are you talking about for live viewing or for photography?

 

[strmrdr]

Something we have to consider is that we are in the middle of the fastest and largest change in interior lighting in history and any light grading has to take the new lighting into account.

 

[strmrdr]

Date: 5/18/2009 12:22:37 PM
Author: Moh 10
Strm, are you talking about for live viewing or for photography?

Both, but if someone wants to discuss one in specific they can specify.

 

[Moh 10]

When you say, " the fastest and largest change in interior lighting in history" are you talking about those new compact fluorescent bulbs?

 

[Moh 10]

This might be a good place to mention that I really like something that GOG does.
Unlike some vendors that using lighting only to make their diamonds look better GOG is transparent enough to provide additional pics that use special lighting to help you understand the inclusions you are getting.

I believe this kind of lighting is called darkfield and it helps you see the inclusions more clearly.
This makes me more comfortable buying from GOG than the vendors that use lighting to make inclusions LESS noticeable.

Of course there are all kinds of customers out there.
I'm sure some would be scared away by pics that point out the inclusions.
This may mean GOG gains the business of certain kind of customers but looses that of others.

 

[strmrdr]

Date: 5/18/2009 12:30:33 PM
Author: Moh 10
When you say, '' the fastest and largest change in interior lighting in history'' are you talking about those new compact fluorescent bulbs?

cf is just the tip of the iceberg and is already old tech.
It is not efficient enough and contains mercury which will prevent it from being the long term solution.

 

[strmrdr]

Date: 5/18/2009 12:45:53 PM
Author: Moh 10
This might be a good place to mention that I really like something that GOG does.

Unlike some vendors that using lighting only to make their diamonds look better GOG is transparent enough to provide additional pics that use special lighting to help you understand the inclusions you are getting.


I believe this kind of lighting is called darkfield and it helps you see the inclusions more clearly.

This makes me more comfortable buying from GOG than the vendors that use lighting to make inclusions LESS noticeable.


Of course there are all kinds of customers out there.

I''m sure some would be scared away by pics that point out the inclusions.

This may mean GOG gains the business of certain kind of customers but looses that of others.

Right it is called darkfeild, great for seeing inclusions and very bad for judging performance.
It is a nice part of an information package but not suitable for being the only image.

 

[Regular Guy]

Me and my guys support this effort...

 

[Stephan]

A diamond should always be considered in different lighting conditions and from different distances.

 

[Serg]

Date: 5/18/2009 12:03:17 PM
Author: Moh 10
I know it''s controversial, but what about the GIA Diamond Dock?


At least it is a currently-available single standard from a recognized authority that everyone could get.


Even if it is not perfect having one standard that everyone uses is a huge improvement over what we have today.

Some Critical DD problems:
1) back lighting( improve diamonds with strong leakage)
2) too short distance between light source and diamond, what produce wrong ratio between brightness background and primary light source brightness .
3) Light is absent in very important( standard) directions

 

[Moh 10]

Okay, sorry I mentioned it.

DD is outahere!

 

[DiamondFlame]

Seeing how many solitaire designs elevate the center diamond well above the finger allowing light to enter through the pavillion, would this not be considered a form of ''backlighting''?

What could be considered a realistic environment behind the diamond? Or realistic head obstruction?
Because the term ''realistic'' is unfortunately ''subjective''.

 

[strmrdr]

Date: 5/18/2009 1:17:57 PM
Author: QueenMum
A diamond should always be considered in different lighting conditions and from different distances.

Name 4 of each you think should be used.

 

[strmrdr]

Date: 5/18/2009 1:27:29 PM
Author: DiamondFlame
Seeing how many solitaire designs elevate the center diamond well above the finger allowing light to enter through the pavillion, would this not be considered a form of 'backlighting'?

not really but its not the same as a black background either, skin is somewhat reflective

What could be considered a realistic environment behind the diamond? skin tone, 4 prong setting Or realistic head obstruction? equel to 1/2 and full arm length of the average female using the skin tone and hair color average for females as well as size.

Because the term 'realistic' is unfortunately 'subjective'.

 

[Stephan]

Date: 5/18/2009 1:30:04 PM
Author: strmrdr
Name 4 of each you think should be used.

I will only name 2 lighting conditions:
1) Outside, blue sky, northern light without sun
2) Spot/halogen lighting (yes, like in a jewelry

)

I don''t need the white neon lighting (used by all the people in the diamond business I met) to judge performance (but well to judge color).

4 viewing distances:
20, 35, 65 and 200 cm (last one only with spot lighting to judge fire intensity)

 

[Judah Gutwein]

Storm,

There are multiple lighting conditions that would effectively showcase a diamond without unfair enhancements and/or distortions.
These two companies manufacture lighting instruments that are conducive for properly assessing/viewing (and therefore conducive, by extension, for properly photographing) loose diamonds.

OTT
Dazor

Having said that, it is no easy task to try and take a conducive lighting environment for viewing diamonds...and extending that to a similar result in capturing/photographing diamonds, since you have now introduced a new element (camera) into the equation. The camera itself needs to be set to the type of settings that would not distort, manipulate, or fail to accurately capture the visual balance created by the right lighting environment.

Making sure the camera accurately represents the viewer is tough.

Best,

 

[strmrdr]

Date: 5/18/2009 2:37:24 PM
Author: Judah Gutwein
Storm,


There are multiple lighting conditions that would effectively showcase a diamond without unfair enhancements and/or distortions.

These two companies manufacture lighting instruments that are conducive for properly assessing/viewing (and therefore conducive, by extension, for properly photographing) loose diamonds.


OTT

Dazor

Best,

Actually they are exactly the wrong lights and a problem with the industry.
The first is a full spectrum tube on a stick the second link has those and some led lights.
Neither represents what a consumer will see in the real world.
Both can be very deceptive.
LED light can make any diamond sparkle and diamonds in tweezers under tubes on a stick are deceptive because they hide leakage by lighting the pavilion.

 

[strmrdr]

Date: 5/18/2009 2:37:24 PM
Author: Judah Gutwein
Storm,

Having said that, it is no easy task to try and take a conducive lighting environment for viewing diamonds...and extending that to a similar result in capturing/photographing diamonds, since you have now introduced a new element (camera) into the equation. The camera itself needs to be set to the type of settings that would not distort, manipulate, or fail to accurately capture the visual balance created by the right lighting environment.


Making sure the camera accurately represents the viewer is tough.


Best,

This part I agree with.
It is not easy.

 

[Judah Gutwein]

Storm,

I''m not talking about using the LED''s in a non controlled environment. The Dazor light in particular (this being the light that indeed employs LED''s) features a diffuser which does the following:

"Double-sided diffusion filters soften the LED light to provide a uniform source of pure white light".

Yes, LED''s without a diffuser are deceptive, in the same vein that halogens are deceptive. However, they are only deceptive vis a vis showcasing true and accurate light performance in loose diamonds. This however, is not the intended purpose of the light.

With respect to the OTT, tradespeople will sometimes use these products to view diamonds and to quickly assess (approximate) coloration in uncertified stones. This would be a difficult task and ineffective with extreme distortion.

The OTT/Dazor is not structured to showcase or to minimize light performance or light leakage in loose diamonds. That is what the reflector and other technologies are for. I read your title literally since you did not specifically indicate ''LIGHT'' performance.

My response is predicated by my understanding of your premise.

 

[oldminer]

1. You can use LED's or other lighting, but it must be diffused lighting. You can readily diffuse LED lighting and it remains very consistent over the longest time.

2. You place a certain amount of 'head obstruction" into the lighting model because you do not want to measure glare from a direct table reflection to your eye or to the digital sensors.

3. You use a fairly narrow angle off the perpendicular to the table to light the diamond being tested. Most light comes from overhead and not at an angle closer to perpendicular to the girdle.

4. Any lighting model you use should remain the same for ALL diamonds being measured for light return. Of course, this limits cutter's choices to an extent, but real world lighting and the lighting of the model ought to be somewhat reasonably the same. We can argue over tiny details, but you would not want to use an unusual, non-natural type model for lighting. Pick one and go with it. This is what ImaGem did some years back and has never needed to revise it.

5. no back lighting, correct., realistic environment behind the diamond, we use black because we measure all light returned, realistic head shadow/obstruction, yes.

I know this is a forum and it is good to present views and ideas. We should definitely look at the existing working models, such as GEMEX and ImaGem as well as any other models already in place.

 

[strmrdr]

Date: 5/18/2009 3:45:55 PM
Author: Judah Gutwein
Storm,


I''m not talking about using the LED''s in a non controlled environment. The Dazor light in particular (this being the light that indeed employs LED''s) features a diffuser which does the following:



''Double-sided diffusion filters soften the LED light to provide a uniform source of pure white light''.


Yes, LED''s without a diffuser are deceptive, in the same vein that halogens are deceptive. However, they are only deceptive vis a vis showcasing true and accurate light performance in loose diamonds. This however, is not the intended purpose of the light.


With respect to the OTT, tradespeople will sometimes use these products to view diamonds and to quickly assess (approximate) coloration in uncertified stones. This would be a difficult task and ineffective with extreme distortion.



The OTT/Dazor is not structured to showcase or to minimize light performance or light leakage in loose diamonds. That is what the reflector and other technologies are for. I read your title literally since you did not specifically indicate ''LIGHT'' performance.


My response is predicated by my understanding of your premise.

ok I assumed everyone would know I was talking about light performance.

 

[Serg]

Date: 5/18/2009 4:00:37 PM
Author: oldminer
1. You can use LED's or other lighting, but it must be diffused lighting. You can readily diffuse LED lighting and it remains very consistent over the longest time.


2. You place a certain amount of 'head obstruction' into the lighting model because you do not want to measure glare from a direct table reflection to your eye or to the digital sensors.


3. You use a fairly narrow angle off the perpendicular to the table to light the diamond being tested. Most light comes from overhead and not at an angle closer to perpendicular to the girdle.


4. Any lighting model you use should remain the same for ALL diamonds being measured for light return. Of course, this limits cutter's choices to an extent, but real world lighting and the lighting of the model ought to be somewhat reasonably the same. We can argue over tiny details, but you would not want to use an unusual, non-natural type model for lighting. Pick one and go with it. This is what ImaGem did some years back and has never needed to revise it.


5. no back lighting, correct., realistic environment behind the diamond, we use black because we measure all light returned, realistic head shadow/obstruction, yes.


I know this is a forum and it is good to present views and ideas. We should definitely look at the existing working models, such as GEMEX and ImaGem as well as any other models already in place.

[/quote]

Dave,
re:such as GEMEX and ImaGem as well as any other models already in place

Gemex uses ring light models what create some problems:
1) Gemex light scheme do not account body obscuration
2) Gemex head obscuration is not correct model for human head specially in horizontal plane. Distances from left(right) eye to left and right head boundary are quite different. Tolkowsky RBC uses such peculiarity very well.( just check Table-Crown rays)/Not all cuts with high Gemex grade use it
I do not know ImaGem light schema , I suppose it has similar problems

 

[Serg]

also Gemex ring light schema can produce resonance for diamond with high level optical symmetry. Such resonance is not possible in "natural consumer" light scheme, because such light has not symmetry

 

[oldminer]

I don''t think ImaGem has anything of a "simlar problem" in its lighting model compared to Gemex. Both of these models are out in the public domain for examination and possibly there are others such as GIA''s attempt with its Diamond Dock. Subjective grading is all well and good, but in these scientific days, we surely ought to be looking at objective grading and making the system well defined. Another subjective system on top of the existing color and clarity schemes will not make things much easier.

 

[Regular Guy]

Date: 5/18/2009 5:05:31 PM
Author: oldminer

I don't think ImaGem has anything of a "simlar problem" in its lighting model compared to Gemex....

... but in these scientific days, we surely ought to be looking at objective grading and making the system well defined.

 

[strmrdr]

Sergey,
Criticizing others thoughts without posting your own does not help.

 

[oldminer]

Reguler Guy; What does your "smiley" comment indicate. Is it constructive, critical, sarcastic, nothing, something? I doubt anyone but you knows. Let us know what you think.