Maximizing brilliancy is an oversimplificaton

[oldminer]

In the quest to bring information to consumers many of us have simplified our limited understanding of light behavior in presenting it. People now say that want maximum light return from diamonds. A few sellers and gemologists actually already know what they mean, but I think it is important for everyone to understand that what is wanted is a highly appealing diamond, a beautiful one, not a bright, white mirror or a 150 watt light bulb.

If you are watching TV and bring up the brightness to maximum, you won''t like the picture. So, you reduce brightness to a somewhat lower level and then adjust the contrast to suit your taste. This equates, in simple terms, to white light return and scintillation / intensity.

Neither brightness or contrast is actually "maximized", but the appealing nature of the image might be called "ideal".

The you might bring the brightness or contrast up or down a few notches, again adjusting them to suit your eyes and taste finding there were other setting equally appealing and worthy. These are also possibly "ideal", too.

A very similar thing is going on with diamonds. Many different combinations have high appeal to the eyes. Ultimately you are the best judge. We can help you make a good selection, but there is definitely more than one specific combination of light return, scintillation and intensity that could be called "ideal". This is all a very recent addendum to the traditional approach to what makes an ideal cut diamond, but you need to get a handle on this as you search for a fine diamond. It widens the possible choices and allows some room in tight budgets because not every beautiful diamond is cut the same as every other and prices sometimes are driven not by looks, but by traditional parameters of cut. You can hunt out some super values in these special, non-traditional type "ideal" looking stones.

This can be done by you with a Ideal-Scope if you are examining actual stones. Via the Internet, it can be done with transmitted images from the Ideal-Scope, Isee2, BrillianceScope, Firescope, and a couple others, too. Even better technology is in the wings, but there is no reason to wait or avoid thinking about using these great methods now.

 

[moremoremore]

Thanks Dave....very informative and well said as usual...It's funny- My brain knowns what "ideal" is and what to look for... but my eyes make the final decision on what is visually pleasing and what to buy!

 

[69gm]

leave it to dave to put things into terms even a GUY like me (gasp) can understand.

an electronics comparison...how perfect is that for us guys, huh?

thanks dave! as always, great views and info.

 

[Paul-Antwerp]

You are very right, Dave, the concept of contrast is a very important factor to understand. One can find a very good read on it on www.idealscope.com, in newsletter 3.

However, the concept of brilliancy is not exactly the same as that of light return.

Remember the head-obscuration (or head-shadow, or whatever we call it nowadays), which is a major part of contrast. So, you have light return, which does not necessarily translate in brilliancy. Only, when you start tilting this stone, you will have other light windows becoming dark while the dark ones light up.

It is this play of dynamic contrast, which is extremely appealing.

Live long,

 

[Serg]

----------------
On 6/8/2004 10:50:22 AM Paul-Antwerp wrote:

You are very right,
Remember the head-obscuration (or head-shadow, or whatever we call it nowadays), which is a major part of contrast.

Live long,----------------

Sorry Paul , I think it is other simplified and misleading idea( like LR=Brilliance)

 

[Serg]

head-obscuration is major reason of contrast for ambient light only( like hemisphere light)

 

[Hest88]

Thanks Dave. Very good explanation.

 

[Paul-Antwerp]

Sorry Serg,

You are right. It is a difficult balance between keeping it simple and completely correct.

Other light conditions then again will cause more visible fire. Am I correct in this simplification?

Live long,

 

[Serg]

----------------
On 6/8/2004 11:46:33 AM Paul-Antwerp wrote:

Sorry Serg,

You are right. It is a difficult balance between keeping it simple and completely correct.

Other light conditions then again will cause more visible fire. Am I correct in this simplification?

Live long,
----------------

Paul, I think it is not simplification , it is generalization.
Any other light conditions will give more visible fire.

 

[love rocks]

So...just curious...what's the best lighting in which to view a diamonds' brilliance/fire?

I mean, I know that most jewelry stores have overhead lighting - it just makes any stone look prettier - should I also be checking a diamond's light return under other conditions, such as "normal" fluourescent lighting (i.e. the "other" overhead lights in the store)?

Since that would be the kind of lighting I would be looking at my diamond in everyday, anyway?

What does the difference in appearance of the diamond under these different conditions say about the "performance" of the rock, anyway? (if it's brilliant under one lighting, but not the other, is it still considered a good "performer"?)


TIA

 

[antigoon]

I think that David's comments about not relying only on light return are bang-on. However, despite his best intentions, I don't think they're helpful or informative to the average consumer at all.

"Don't pay attention to light return alone, look at all the qualities of a diamond: return, scintillation and intensity" is my paraphrasing of the main thesis. That's all very well, but exactly how do we measure these things? DiamondCalc, Isee2, Brilliantscope? As many people will tell you the BrilliantScope is bogus pseudo-science as will tell you it's the best thing since sliced bread. How do we measure it, and who do we trust? At least with light return (via the firescope), the average consumer has a simple and reproduceable way to further evaluate an ideal diamond.

My little rant on the lack of leadership from the grading organisations...

While "Even better technology is in the wings", that's not what we need, at least not right away. What's really missing here isn't more advances from diamond companies (Octonus, Brilliantscope, Sarin) who, however well meaning, can't help but have a little conflict of interest. What's really missing is some leadership from the grading organizations (AGS, GIA, HRD, etc.). As a consumer, I want a statement from them stating what their positions are on all of these tools (isee2, idealscope, diamondcalc, etc.).
Well, first of all, I want a new cut grading system that will properly reflect the quality of the cut of a diamond. Then, the rest of this discussion would be largely moot.

Steve

 

[pqcollectibles]

The cut grading system is changing. There was a huge discussion about it a while back. It just hasn't arrived quite yet.

https://www.pricescope.com/community/threads/gia-nears-release-of-diamond-cut-grading-system.12530/

Very good explanation, Dave. You explained that in terms so anyone who's ever adjusted the color/contrast/brightness on their computer monitors can understand.

Take your diamonds away from the jewelry store lighting. Look at them in natural light. In candle light. In indirect sunlight. In elevator and office lighting. Move the light source. Move the diamond. Watch how the light plays in and off the diamond.

 

[Serg]

Dave,

As you bring up the topic of customers misleading I want to point that your analogy with TV for contrast explanation is utterly inappropriate in spite of its simplicity and clearness.

You use the same word "contrast" for totally different phenomena.
1) Technical value: the difference between maximum and minimum intensity when DISPLAYING an image (for example on TV where you can adjust it with "contrast" adjustment knob).
2) One of psychophysiological perceptions and evaluations of an image: the difference in the own contrast between two different images for the same contrast knob position on TV. This difference is determined by the image itself but not the TV settings.
With the TV settings you can increase or decrease this difference but not create. Roughly speaking own contrast of image depends on positional relationship, quantity, shapes, sizes, intensities and colors of patches (spots) of image.

If we talk about evaluation of diamond beauty then I suggest to speak about own contrast of diamond but not about TV settings.

I would not like that the same story happened with the Contrast as it was with LR. All these simplifications for customers cost really too expensive for industry.

With the difference between minimum and maximum (or similar characteristics) it is impossible to describe adequately a human perception of even simple scenes.

 

[strmrdr]

One thing Iv noticed is that the experts tend to talk about different aspects of the performance of diamonds without specifying the lighting conditions they are talking about.
This makes it a little confusing for those that don’t know enough to tell what light conditions they are talking about.
Diamonds behavior is very dependant on the lighting because they do not generate light of there own instead they return available light and do so in different ways depending on what type and intensity of light is available to return.
This is the reason it is not easy to get a handle on and likely the source of a lot of the disagreement over what is actually happening and why.

My very non-expert take on it:
Bright direct light – performance in a large part is determined by the efficiency of the pavilion reflectors ability to return a large amount of light and how well the crown facets break up and bend that light creating fire.
A diamond having good pavilion reflectors but poor ability in the rest of the diamond to bend and break up that returned light will look like a spot light and is what oldminer is getting at.

On the other hand a diamond that has poor pavilion reflectors but has the ability to create a lot of reflections/fire from the crown will appear a little dull in bright light but put it in shifting light and it will display a ton of fire. Example: most pear shaped diamonds.

Then there is diffused lighting that isn’t bright enough for the pavilion reflectors to really kick in and not directional enough to cause fire to be returned in a visible amount and direction this is where the arrow pattern is displayed on h&a diamonds and the step pattern on asscher diamonds really come into play.

The real key and the goal is to find a cut parameter that maximizes the appearance in all light conditions in the same diamond.
The problem comes in that something that for example creates more fire may interfere with maximizing light return.
And getting a nice looking pattern may not be optimal for creating light return or fire.

Ps.
I still wonder how much wavelengths and intensity have to do with a lot of this versus just being direct or indirect light but that’s a subject for another thread.

 

[Paul-Antwerp]

Storm,

Sorry if we are not clear enough, but your summary is not correct.

Let us take the round brilliant, super-ideal cut.

In hemispheric lighting conditions (office lighting) with a viewer, you have a combination of maximum brilliance and contrast (in the arrows and the minimal light leakage around the girdle).

That same stone will give great fire in all other lighting conditions. In fact, brilliance is not the enemy of fire. This is only true in the case of hemispheric lighting conditions. In other lighting conditions, that same stone is extremely fiery.

So, there are definitely combinations that deliver a great combination of brilliance, fire, scintillation and contrast.

In some fancy colours however, the aspect of light return can become confusing, since one can have stones (for instance princesses) returning a lot of light to the viewer, but because the head obstruction does not play, this stone can have almost no contrast. In that case, one needs light leakage in order to get contrast.

There are two important things to remember:
1. Brilliance is not the enemy of fire. What you observe, depends on the lighting conditions.
2. Light performance is not the same as light return, since light leakage might, depending on the case, add to the performance of a diamond, mostly in adding contrast, and thus also scintillation.

Live long,

 

[oldminer]

Wow! What a wonderful set of responses. I admit that there is much more for me to learn on this subject, even at a simple level. My intention was to open a subject for discussion that might highlight the very difficult issues facing gemologists, scientists, diamond dealers and consumers. We suffer from a lack of agreement on the definition of some basic terms. We consider variables that exist that may or may not have significant impact on "beauty", but ones that arguably are possibly of importance. I think the analogy of the brightness and contrast controls on the TV make an informative comparision as a teaching tool for the under-educated, not as a defining theorem of how all this works. Admittedly, the analogy may be flawed in the way words are defined, but there are valid characteristics of this that many will use to begin to grasp the concept of maximum light return does not always means maximum beauty.

I had no analogy for dynamic brilliancy or sparkle (scintillation) and of course this is very important to light behavior in faceted gems.

One further thing I'd like to throw out for discussion is to waht extent does dispersion, fire, have on our individual or mutual perceptions of overall "beauty"? My own opinion is that dispersion is an attribute of a finely cut diamond, but not terrifically important to how the diamond will be judged for overall appeal. I see dispersion as a variable that makes little difference.... Now, there may be differing opinions.

I will say that a diamond such as the 8Star, a branded diamond, cut for higher than regular dispersion, could be a "Branded" product based on a consistently high amount of this one variable. That is quite legitimate, but in what we accept as ideal cut diamonds, does dispersion make the short list of variables that really make us select on stone over another????

What is your thoughts on this?

THANK YOU for your participation. I doubt there is a better forum for discussion of these topics anywhere.

 

[strmrdr]

Paul,
Thanks for proving my point about light conditions.
I kinda fell into the same trap I complained about.

Is it just this line:
"The problem comes in that something that for example creates more fire may interfere with maximizing light return.
And getting a nice looking pattern may not be optimal for creating light return or fire."
that there is a problem with or am I missing the boat with the rest of it too?

 

[strmrdr]

oldminer
imho the more a diamond gets noticed by the owner the better its liked.

For example how many times have we heard I love my diamond it was someplace the other day and noticed that it was sending awesome flashes of light on a wall etc?

8* hit on something there with the broader more noticable flashes of light that get reflected back to the owners more often.

 

[scotch]

----------------
On 6/9/2004 6:28:51 AM Serg wrote:


You use the same word 'contrast' for totally different phenomena.
1) Technical value: the difference between maximum and minimum intensity when DISPLAYING an image (for example on TV where you can adjust it with 'contrast' adjustment knob).
2) One of psychophysiological perceptions and evaluations of an image: the difference in the own contrast between two different images for the same contrast knob position on TV. This difference is determined by the image itself but not the TV settings.
With the TV settings you can increase or decrease this difference but not create. Roughly speaking own contrast of image depends on positional relationship, quantity, shapes, sizes, intensities and colors of patches (spots) of image.----------------

Serg:

Along the lines of what strmrdr (Hey strmrdr, can I buy you a vowel?

) said about the mutual influence of the stone itself vs. the lighting conditions it is viewed in: would you say that the following analogy applies to your differentiation of "technical brilliance" vs. "perceived brilliance":

1) The lighting conditions: Viewing the same stone in different lighting conditions. As there is an optimal setting for contrast on your TV, there would be an optimal lighting condition for judging brilliance in a diamond. That should be the reference setting, e.g. diffuse white light of a certain intensity. In that condition, contrast should be caused mainly by the presence of head shadow. If you eliminate head shadow, you should ideally have no contrast, but rather pure white light reflected to you. Any remaining black/white difference would indicate light leakage and would be considered a negative influence.

I found this little experiment suggested by Garry Holloway extremely instructive: You take a clean white sheet of paper, poke a little viewing hole in it, and peek at the diamond through that little hole in diffuse light condition, holding the paper in between your face and the diamond. This eliminates head shadow. When I did this with my wife's diamond, I saw mostly white, with some darker or off-white areas indicating partial leakage hrough the pavilion or reflection in directions other than straight back into my eye.

2) Looking a two different stones in identical, "reference" light condition. That would be the equivalent to setting the TV to optimal contrast, e.g. such as is done by a TV technician using a reference black and white pattern. Any difference in perceived contrast should be due to differences in the stones themselves. Now if you subject both stones to this procedure: First, you eliminate head shadow, e.g. as in Garry's experiment. Next, any remaining black/white difference from light leakage should be eliminated, e.g. by introducing light entering from the pavilion. Now you should see all white. Lastly, you reintroduce head shadow, and compare the resulting picture.

The problem that remains: How do you eliminate factors such as symmetry, and differences in perception such as: what is more beautiful, the same amount of black, concentrated in few larger areas, or dispersed over more, smaller areas?

----------------
I would not like that the same story happened with the Contrast as it was with LR. All these simplifications for customers cost really too expensive for industry.----------------

That is a little bit of a cryptic comment, could you please elaborate on what you are referring to?

----------------
With the difference between minimum and maximum (or similar characteristics) it is impossible to describe adequately a human perception of even simple scenes.----------------

Wouldn't it be possible to identify all the different aspects of brilliance, be able to eliminate them selectively, and measure each aspect separately? Or at least measure what can be measured, having eliminated what can't be measured, and describe the nonmeasurable aspects in different ways?

Scotch

 

[oldminer]

I would suggest that we consider that being able to measure many parameters, does not really mean every available measurement truly matters much or at all in the final result.

One can gather objective data and falsely suppose every bit of data makes a difference and then try very hard to explain the result from these many bits of data. We are dealing with human perception. One should recognize that not all collected data may affect human perception, and therefore not all data collected may be pertinent to the final, correct result.

That's why I asked about dispersion. Just because we can measure it, does it always have an effect or only in special cases? Other things mentioned in the other replies contain variables which may not make a difference, but can be measured. It is nice to measure all the events, but what are the ones we need to closely evaluate and those which are very much less likely to effect overall results?

 

[solange]

Need Help! Idealscope Image This is another site asking for similar advice and, as a beginner, I find the information very confusing and contradictory. Perhaps the two sites can somehow be coordinated so that various experts can combine their opinions and come up with answers that will be helpful to those of us who are trying to learn what to look for.
It might help non professionals get a clearer picture of what matters and what does not when selecting a stone.

 

[oldminer]

Solange: I think that if you examine what various experts are saying, there is not a whole lot of contradiction. There are different approaches to the final result and some ways to get somewhat different choices, but in the end, if yu can get a simple understanding of the subject, you will be able to select intelligently and buy a very fine looking diamond.

This is what the discussion boils down to anyway. It may always be confusing as it can both be very technical and subjective in the undefined search for an individual's sense of what is beautiful. Beauty is extemely difficult to fully define even for one person. A definition that would suit everyone is pretty much inconceivable.

Just by reading all the above postings, you will know more about the subject than 99% of the world's population knows about it. I'd say that is pretty good for someone who is confused by so much techical information.

 

[glitterata]

----------------
On 6/9/2004 11:54:29 AM oldminer wrote:


One further thing I'd like to throw out for discussion is to waht extent does dispersion, fire, have on our individual or mutual perceptions of overall 'beauty'? My own opinion is that dispersion is an attribute of a finely cut diamond, but not terrifically important to how the diamond will be judged for overall appeal. I see dispersion as a variable that makes little difference.... Now, there may be differing opinions.


I will say that a diamond such as the 8Star, a branded diamond, cut for higher than regular dispersion, could be a 'Branded' product based on a consistently high amount of this one variable. That is quite legitimate, but in what we accept as ideal cut diamonds, does dispersion make the short list of variables that really make us select on stone over another????


What is your thoughts on this?

Dave, are you asking whether people who buy diamonds care whether they give off fire, or whether they perceive a diamond with a higher dispersion score as fierier?

I certainly care about fire. I far prefer diamonds that shoot off lots of sparks of color to ones that give off white light and glitter from black to white, but give off little color. I bet many people here agree with me. If not, why wear diamonds, rather than (say) white sapphires?

If you're asking whether diamonds that score high for dispersion appear to the eye to be fierier than other diamonds, I can't answer that question. It seems like they should, but I guess you'd have do some tests and comparisons to find out.

 

[oldminer]

QUOTE:
Dave, are you asking whether people who buy diamonds care whether they give off fire, or whether they perceive a diamond with a higher dispersion score as fierier?
RESPONSE:
I am asking the first part, not the second. Sure, people want a diamond to look diamond-like, having some degree of fire. Do they perceive am amount? Is a certain amount important? I don't think it is a crucial element for most consumers.
xxxxxxxxxxxxxxxxx
QUOTE:
I certainly care about fire. I far prefer diamonds that shoot off lots of sparks of color to ones that give off white light and glitter from black to white, but give off little color. I bet many people here agree with me. If not, why wear diamonds, rather than (say) white sapphires?
RESPONSE:
Okay, you like some dispersion. Me too. All finely cut diamonds shoot off dispersion due to the way they are cut. It is a constant part of finely cut stones. Does exactly a certain amount make a difference? That is the question.
White sapphires are dead dogs compared to diamonds. Lower refractive index, less brilliancy, lower amount of luster and polish, more light leakage. Missing fire is hardly the major fault although admittedly there is little to no dispersion.
xxxxxxxxxxxxxxxx
QUOTE:
If you're asking whether diamonds that score high for dispersion appear to the eye to be fierier than other diamonds, I can't answer that question. It seems like they should, but I guess you'd have do some tests and comparisons to find out.
RESPONSE:
Diamonds with lots of fire may appear more dispersive. I was NOT asking that fairly obvious question. The answer is readily apparent and logical. Does it matter? That's the issue. Is a little more or a little less fire the thing that dictates a positive or negative assessment of beauty? I don't believe it generally does although I pointed out the 8* stone which hang's its brand on perfection in cutting and high amounts of fire.
xxxxxxxxxxxxxxxxxx

RESPONSE:

 

[glitterata]

Hey, Dave, I realize my response sounded really--what's the right word?--pompous? something like that. As if I thought I was some sort of knowledgeable person, which I'm not.

I still think fire is high up on my list of desireable qualities in a diamond.

 

[Paul-Antwerp]

What I really liked in the Moscow-presentation of AGS, is that they assessed a diamond in different lighting conditions and at different distances.

They found that in specific combinations of light and distance, cut had little effect on the light performance.

That is why they want to describe their future cut-grade as pertaining to those diamonds that have the highest likelyhood to perform better in most different conditions of light and distance.

Take the example of a poorly cut diamond, with a lot of light leakage. In office lighting, this stone can still show a lot of fire. On the other hand, a super-ideal cut diamond, in the same office lighting, will return mostly white light, and less fire. This does not mean that the poorly cut diamond shows more fire. Because in other lighting conditions, the fire of the super-ideal will clearly outperform the fire of the other one.

Live long,

 

[strmrdr]

oldminer wrote:
"Is a little more or a little less fire the thing that dictates a positive or negative assessment of beauty?"

..........................
No but it having enough to draw attention to itself at times is a real plus.
How much is enough is really impossible to answer because it will depend on the person and the typical lighting they are in day to day.
imho buying a diamond that is too tilted performance wise towards one light source isn’t the right answer.

Lets be fair 8* while they sell it on the fire has more going for it than just that.

This is weird cuz here I am touting 8* and I don’t really like the company nor its owner and don’t care for their marketing hype either.
While they are good I think there is the equal or better available for a lot less money.

Anyway back to the point:
Jewelry after a while just becomes another piece of clothing that is worn and not noticed unless it calls attention to itself.
Fire is one way diamonds call attention to themselves but there are other ways also.
A diamond that is all fire and little light return will look just as bad as a diamond that’s all light return and little fire it just does it under different light conditions.
There needs to be a balance and a real beautiful diamond is one that looks awesome under all light conditions.
It wont look the same under all light conditions that is impossible but it can still look great under the different lighting conditions.
The definition of great is what varies.

My answer on what is great performance is I will know it when I see it :}
Which doesn’t help someone trying to come up with a cut grading system at all now does it? :}

 

[glitterata]

I think I'm not really clear on the relationship (or difference) between dispersion and refractive index. How does fire relate to refractive index, if at all?

 

[oldminer]

Dispersion is potentially greater in a material with a higher refractive index.

Dispersion occurs when white light is separated into its range of colors, such as when a prism is employed to make a rainbow from white light. The higher the RI of the glass used to construct the prism, the wider the rainbow would appear at a given distance.

The Refractive Index is a scale indicating the optical density of the material. In simple terms it compares air to the matrial being tested. An 1.76 - 1.77 found in corundum (sapphire-ruby), bends light 1.76 to 1 in realtion to how air bends light.

RI can be seen when you put a pencil in a glass of water and see how the pencil then appears bent or displaced. This is the higher RI of water versus air. Gemstones have a far higher ratio of bending light than water.

So, knowing these things, a high RI material always bends light more than a low RI material. The fire from a material cut to angles that create dispersion (fire) is potentially greater when the material has a higher RI.

In reality, one can extract a lot of fire from rather low RI material by cutting angles that create dispersion, but brilliancy will be sacrificed. The same can be done with diamonds. Diamonds have a very large potential for dispersion, but cutting for best overall performance eliminates a lot of the potentially visible dispersion. 8* gives a little more fire while retaining much of the overall performance.

Just to add a bit more confusion, a doubly refractive material may more readily show dispersion than a singly refractive material. Diamonds are singly refractive and inherently less dispersive than a doubly refractive, similar RI material. This applies to Moissanite and a couple other doubly refractive diamond imitations that have a little or way too much dispersion to look authentic.

Moissanite can be made singly refractive as the shape of its crystal growth can be altered. However, I don't believe cubic silicon carbide (moissanite) is commercailly produced. Normally Moissanite is doubly refractive.

 

[verticalhorizon]

If diamonds can be made to increase dispersion at the sacrifice of cut, then how does the Jubilee fit into the picutre which seems to be cut well and also have a high level of dispersion? (Of which I was on the fence of thinking was too much of a good thing at one point. Again the issue of perhaps contrast.)