A Diamond ‘Thought Experiment’

[Garry H (Cut Nut)]

Think about this ‘thought experiment’. Take a diamond or a ring and start looking at it toward the ceiling lights. Yuck? Then slowly move it down and find the best sparkle. Then facing the floor your head is between the lights blocking them Yuck!

Where are the lights. Can the diamond see the lights? Is your head blocking the lights?
No light = no diamond. Diamonds cease to exist in the dark ☹
If your head blocks the lights, there is less light.
If the diamond only gets its light from walls, it will not have much sparkle.
There are more sparkles with small lights than big tube lights.

Sadly, the GIA developed it’s cut grade using a really bad lightbox that favored deeper cuts. The IGI recently did a study and now prefers slightly shallower cuts. Ones that perform well with the Ideal-Scope.

Most fancy cut shapes will perform a little differently to most round diamonds. That is why we use an ASET scope for fancies.

 

[Karl_K]

In a dark basement with no light, a potato is as sparkly as a diamond.

 

[oncrutchesrightnow]

In a dark basement with no light, a potato is as sparkly as a diamond.

Needs a halo.

 

[Garry H (Cut Nut)]

Needs a halo.

The girl or the diamond?

 

[oncrutchesrightnow]

The girl or the diamond?

The potato.

 

[freddyboston]

Eureka !!! A use for the free lab diamond studs you get from some vendors.....

 

[jjca]

Eureka !!! A use for the free lab diamond studs you get from some vendors.....

Genius - I wish I had some free lab studs to put in a spud!

 

[DejaWiz]

Eureka !!! A use for the free lab diamond studs you get from some vendors.....

 

[Garry H (Cut Nut)]

Fun thread jack, but has anyone actually bothered to do the simple test?
I know it is beneath most of you, but you might be surprised?

 

[Rockdiamond]

Fun thread jack, but has anyone actually bothered to do the simple test?

Yes I did as soon as I read it. Durn stone looked so dead above my head
My love of photography, combined with love of diamonds has given me a lot of insight on working the light for the specific stone.
It was a contentious issue on PS way back when. Folks accused me of using dubious methods to “back light “ diamonds.
The truth was that I knew how to properly use the light in a way the camera understood.
The issue with every commercially available method of photography is that it’s standardized- and diamonds are anything but.
Your graphic example is pretty much spot on in general.

 

[Garry H (Cut Nut)]

Yes I did as soon as I read it. Durn stone looked so dead above my head
My love of photography, combined with love of diamonds has given me a lot of insight on working the light for the specific stone.
It was a contentious issue on PS way back when. Folks accused me of using dubious methods to “back light “ diamonds.
The truth was that I knew how to properly use the light in a way the camera understood.
The issue with every commercially available method of photography is that it’s standardized- and diamonds are anything but.
Your graphic example is pretty much spot on in general.

Thanks David, and apologies for being one of those 'backward' people

 

[DejaWiz]

Fun thread jack, but has anyone actually bothered to do the simple test?
I know it is beneath most of you, but you might be surprised?

Yes, have done this numerous times over the years while just looking at diamonds.
Light = needed for a diamond to reflect it back to our eyes.
Obstruction, type of lighting, and intensity of lighting are all factors that we should all be aware of.

 

[0-0-0]

Get light colored floors!

 

[Garry H (Cut Nut)]

Get light colored floors!

Actually 000 - dark floors show diamonds off best because of the contrast effect.
One of the reasons diamonds look dark when you look at them with a bright background!

 

[0-0-0]

I have rooms with light beige/white floor tiles and rooms with light brown floor carpet in the house, with the same lighting and paint and cabinet colors. The diamonds look better in the rooms with the brighter light beige/white floor tiles.

 

[Garry H (Cut Nut)]

I have rooms with light beige/white floor tiles and rooms with light brown floor carpet in the house, with the same lighting and paint and cabinet colors. The diamonds look better in the rooms with the brighter light beige/white floor tiles.

I am talking very dark vs very light when the floor is the background 000

 

[Texas Leaguer]

@Garry H (Cut Nut) ,
Just focusing on your last statement about using ASET for assessing fancy shape light performance. I agree it is a great tool, but understanding ASET signatures for fancies is not so simple. Fancy shapes are so variable in appearance that basic understanding of ASET is not adequate.

You can learn much about how a fancy shape diamond is handling light based on ASET, but predicting the eye appeal is another matter. I think you have to have a lot of experience with fancies and ASET to be able to translate light maps into predictors of actual appearance.

I'm sure this is one of the challenges AGS had in developing their light performance cut grading system for fancies, and what GIA is probably struggling with now in hopes of expanding their overall cut grade beyond just rounds.

 

[autumngems]

Eureka !!! A use for the free lab diamond studs you get from some vendors.....

Seriously, lol

 

[Garry H (Cut Nut)]

@Garry H (Cut Nut) ,
Just focusing on your last statement about using ASET for assessing fancy shape light performance. I agree it is a great tool, but understanding ASET signatures for fancies is not so simple. Fancy shapes are so variable in appearance that basic understanding of ASET is not adequate.

You can learn much about how a fancy shape diamond is handling light based on ASET, but predicting the eye appeal is another matter. I think you have to have a lot of experience with fancies and ASET to be able to translate light maps into predictors of actual appearance.

I'm sure this is one of the challenges AGS had in developing their light performance cut grading system for fancies, and what GIA is probably struggling with now in hopes of expanding their overall cut grade beyond just rounds.

Here is a tip for you and everyone else Bryan.
Tilt the stone left to right (in the axis orientation it would most likely be set) about 5-10 degrees.
This gives you an idea how the diamond will appear to two eyes.

I made these videos 20 years ago on Ideal-scope site:

Using Aset Scopes - Ideal Scope

ideal-scope.com

 

[Rfisher]

Sadly, the GIA developed it’s cut grade using a really bad lightbox that favored deeper cuts

What position of the girl in your illustration closely resembles GIA’s light box?

The IGI recently did a study and now prefers slightly shallower cuts

Same question.

 

[Garry H (Cut Nut)]

What position of the girl in your illustration closely resembles GIA’s light box?


Same question.

For the GIA question - here is an actual experiment that I did and published here and with Sergey, in a journal.

GIA Excellent Cut Grade: Case Study

Introduction At the start of 2006 GIA began, for the first time ever, issuing cut grades for round colorless diamonds. Evidence suggests this system, that was meant to help, could […]

www.pricescope.com

There were several other discussions: https://www.pricescope.com/community/threads/gia-diamond-dock-simple-summary.42538/

For IGI - ask @Karl_K

 

[Karl_K]

For IGI - ask @Karl_K

For the New IGI Round Cut Grading System

We discovered that using a single viewing distance doesn’t accurately represent how people actually observe diamonds in real life.

To better reflect real-world conditions, we studied various viewing distances and incorporated several into our grading methodology.

The most common viewing position by far is with the diamond worn on the hand, held in front and slightly below the face, approximately 15 inches from the eyes.(~1/2 arm length)
The second most common is at full arm’s length, lower than the face but farther from the body.
The third—and least common—is the close-up ASET-style view, around 10 inches from the eye while looking sharply downward.

Interestingly, although we approached the analysis differently, much of our data supported the results of the Holloway Cut Advisor (HCA). The key differences appeared where star% and lower half/girdle% had a noticeable impact on appearance—areas where the HCA uses fixed values, while we used multiple variations.

Our findings also reinforced the importance of star facet length (star%). It plays a critical role in influencing the angle of the upper girdle facets.
In certain cases, such as a shallow crown angle combined with a longer star%, the result can be beneficial. However, with steep crown angles, a long star%—or even the typical 50%—can cause issues, and a shorter star% is preferred.
Shorter star facets allow more room for upper girdle facets to be longer and shallower, which helps prevent them from becoming overly steep in diamonds with steep crowns.