Light Leakage and Light Return

[pricescope]

Sergey calculated the effect of the leakage visible in Idealscope on diamond light return. See picture below.

As you can see from the plot, only if you have near to 100% light leakage (as a window in a stone) you’ll see these areas not reflecting light back to you.

If you have 50% light leakage, you still have 85% of the light return, 87% leakage – 50% light return.

I.e. areas with partial light leakage will still return light to observer eye. It is just a trick of our brain that we see light leakage areas with idealscope (or firescope) very easily.

On another hand, some amount of light leakage can add to contrast, fire and scintillation. There is no guarantee that you’ll like a diamond with no visible light leakage more than a diamond with some limited leakage.

Very strong leakage is bad. However, diamond with no visible leakage not necessary will be prettier than the one with small leakage.

Again, as with HCA, once you found a stone with better than an average idealscope image, don’t split hairs with idealscope, use your eye and other factors to select the best stone for you.

 

[niceice]

Has anybody stopped to consider that if one were to change the angle of the pink cone, that one would change the angle of the "leakage"? Say it's at 74 degrees + - now and it was changed to 45 degrees or even 60 degrees would that not change the amount of what is being described as leakage? Think of it as a lamp shade... A lamp sitting on your desk reflects light down upon the surface of your desk in direct proportion to the angle of the lampshade itself, it is a direct relationship. Change the angle of the lampshade, change the circumferance of the light being reflected upon your desk. All an Ideal Scope, Fire Scope, Light Scope, SymmetriScope, etc. do is reflect light upon the surface of a diamond by use of a pink reflective surface... Change the angle of the pink reflective surface and you've changed the circumferance of the light being reflected off of the surface of the diamond just as you have with the table... Each device could essentially be manufactured with a pink cone that is condusive to making the seller's diamonds look better or "leak" less by changing the angle of the cone so that more or less light is cast across the surface of the stone... What so many people are calling "leakage" looks to us like nothing more than not enough light reaching the ends of the stone... What if we were to add another reflective surface to the picture and direct another light source towards the stone from yet another angle? Would that then change the "leakage" we certainly think so... We're thinking out loud here, anybody care to comment? Perhaps a lighting architect or two? We've mentioned this concept to a few of our engineer type clients and they seem to concur but we haven't taken the time to explore this concept into reality, perhaps this is something that Sergey would be interested in exploring at Moscow University as part of their light return study...

 

[Mara]

So what exactly does this mean for 'tweaked girdle' type stones where the light leakage is almost nil? Would a non-tweaked girdle stone of the same cut caliber be the more appealing/beautiful choice?

 

[strmrdr]

"Again, as with HCA, once you found a stone with better than an average idealscope image, don’t split hairs with idealscope, use your eye and other factors to select the best stone for you."

While that may be good advice it brings up the dilemma of trying to buy diamonds across the net unseen it is not practical for the average consumer to bring in 100 diamonds and pick the best one.
Therefore we have to use what is available and we can get to help decide between various diamonds.
If we discount the scope images, hca, other by the numbers charts or programs how are we supposed to select diamonds on the net?
That brings us back to trusting the vendor, lets say we find 3 diamonds and 3 people we trust say theirs are top .1% ers then what?
To go further lets say I talk to Brian the cutter, Rhino and niceice and they each have 2 diamonds what they say are top-notch diamonds close in price/clarity/color to the other vendor’s offerings.
I trust all of them to point me in the right direction and each of these diamonds will be top notch so how do I decide which diamond is the best one for me?
Paying to have 6 diamonds sent to an independent appraiser drive an average of 3.5 hours each way with traffic to downtown Chicago to the nearest one isn’t a very good answer.
Neither is saying forget it and paying too much at a local b&m that doesn’t have that quality of diamond in anything but an outrageously priced branded stone.
So what is my answer to picking the best diamond?

 

[valeria101]

It only takes for somone to invent a quality scale for everyone to want to top it. As in : "Is there 'light lickeage' - ok, that must mean that NO light loss is the best". Unfortunately, it is very hard to build up composite (empirical) performance measures for which 'more is better' and 'less is worse' no matter what. No exception here...

Gem cutting is an art, isn't it

 

[Garry H (Cut Nut)]

We have taken Sergey's findings into account in our choice of lighting models (ideal-light) and discussed this issue in our newsletter in December.
http://www.ideal-scope.com/newsletter_issue_003.asp

"Pale pink in the table area is normal. It is not as bad as it appears.

A small amount of girdle leakage aids contrast. The pale area only leaks 25% and returns 75%. "

"Tip: Diamonds with leakage look brighter and more firey in high open backed ring settings, so light can get in the back."

 

[Garry H (Cut Nut)]

Robin & Todd you should read http://www.diamond-cut.com.au/07_gilbertson.htm

I interpreted images based on your concept to formulate some of the raw data for HCA using the Gilbertsonscope on DiamCalc. Al G is now working for GIA on the cut study.

AGS also have used this idea with a 2 colored ideal-scope / firescope idea.
http://www.gemology.ru/cut/english/optical/index.htm
You must read this stuff (some very important people did not even know this had been published until I told them a month ago!!!!)

 

[Garry H (Cut Nut)]

For some reason that image did not work?
Here is another of a Gilbertsonscope

 

[pricescope]

Cut Nut wrote:

----------------
For some reason that image did not work?
----------------

Garry, please remove '%', extra dots and blank spaces from your file names before uploading.

 

[niceice]

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On 4/3/2004 5:02:35 PM Cut Nut wrote:

Robin & Todd you should read ----------------

What does this have to do with what we're saying about the angle of the cone on the various scopes? We understand the concept you are referring to, but that has nothing to do with re-defining what people commonly refer to as "leakage" when it isn't leakage at all... We're not discussing the visual effect of light as seen by the viewer from various angles, we're talking about whether the areas which are not pink in certain areas of the stone as seen through a scope are "leakage" or simply areas where the pink reflection is not reaching or not being reflected into... And we're not making a statement of any kind beyond that regarding any of the devices, we're simply asking "if the angle of the pink cone were changed, would the extent of the 'leakage' change accordingly?"

 

[Garry H (Cut Nut)]

Then sorry R&T but I do not get your point - can you do sketch?

i still think I answered your question

And I have not been drinking (yet

)

BTW can you edit out the underlined - it is hard to read.

Later comment after re and re reading R&T's posts.
I am sure I answered your question / suggestion. The leakage is a result of the light that can enter the pavilion and be seen in the crown through an ideal-scope. Yes you can change the angle of the light that enters the pavilion and that will effect the amount of leakage. 8* did that to their 'enhanced' FS by making the walls black, where as my old model has white reflective walls and would therefore show more leakage.

 

[Garry H (Cut Nut)]

This is an 8* diamond from a Sarin scan and I have used DiamCalc ray tracing to estimate (within about 1%) the amount of light return (not leakage) that would be occurring and what shade of pink you would see in such a stone.

I do not have an actual photograph of the stone - but we have all seen firescope / ideal-scope images of such stones.

 

[Garry H (Cut Nut)]

This time the light return is again in yellow, an the leakage is in blue.
I should be able to find an actual Ideal-scope photo of this stone. Would you like me too folks?

 

[niceice]

----------------
On 4/3/2004 12:19:49 PM strmrdr wrote:

That brings us back to trusting the vendor, lets say we find 3 diamonds and 3 people we trust say theirs are top .1% ers then what?
To go further lets say I talk to Brian the cutter, Rhino and niceice and they each have 2 diamonds what they say are top-notch diamonds close in price/clarity/color to the other vendor’s offerings.
I trust all of them to point me in the right direction and each of these diamonds will be top notch so how do I decide which diamond is the best one for me?----------------

You know the funny thing about this is that Brian, Jonathan and ourselves are so precise in our selection process that we really feel that it's not a matter of which one of us has the better diamond in terms of visual performance, we think they're all essentially the same and many of the gemologists seem to agree when they're sitting their staring at stones from each of us that have been sent over on behalf of a client who is willing to pay for a multi-stone evaluation... And by "we" the reference is being made by Robin and Todd, not the two of us and Brian and Jonathan, we're not trying to speak for them. The deciding factor is usually a combination of clarity / color / carat weight and price... We kind of think that the decision to purchase from one of us over the other isn't really a matter of quality, we all offer an extremely similar and very precise product... Some days it really just comes down to which one of us happens to have the diamond the customer is seeking because our holdings are different from each other in terms of specific stones on any given day... Brian might have a 1.42 carat puppy when we don't while Jonathan has a 1.37 to offer and we only have a 1.62 or something and Brian ends up selling the stone to the customer that day because his stone is closer to what the customer wants - which happens to be a 1.50 carat stone while the budget won't quite reach that far... And a few days later, Jonathan might have the right stone while Brian and Robin and I don't... And then it will be our turn, make sense?

Hey Gary, we have no idea why our post is underlined, we certainly didn't try to underline it... And when we tried to edit it, the result was lines running through the text and that was even harder to read... So who knows what's up... Perhaps something got tweaked when we tried to quote part of your text and edited some of it out because it didn't apply to what we wanted to focus on...

The question is this, if we use your ideal scope as an example - only because you are extremely familiar with it... What we're trying to figure out is, would Sergey's light return analysis pertaining to the ideal scope results and the theory of light "leakage" be different if the angle of the plastic pink insert were changed from like 70 something degrees to say 50 degrees... In other words, are the open white spaces that people call leakage actually leakage or is merely not pink because the angle of the cone is not sufficient enough to cast the reflection of the light far enough across the stone just as the light cast off of one light shade across a table top can be changed in circumferance by changing the angle of the lamp shade.

 

[Garry H (Cut Nut)]

We must have been posting at the same time - see the comments I added in my first answer to your question R&T in the post above

And then go back to bed - it must be late there?

If you mean the angle of the walls of the scope - it would not make any difference - ideally it should be hemispherical - but that was harder to manufacture, and does not make a big deal of difference

 

[strmrdr]

Yes niceice it makes sence but doesnt answer my question.
A little history on this thread:
It was posted in responce to a comment I made in pm in answer to a question about a comment I made on the board.
.........................................

While the following isnt totaly what that conversation was about its what is going thru my mind tonight and when I made the above post and has been for a while.

Im getting a little frustrated.
The "experts" have given us the hca,ideal-scope,aga charts, and a bunch of other tools and tutorials on how to use them ,then when we use them to seperate diamonds that are very close we get told to not be so picky about the readings/images/angles/ratings/what evers.
It cant be both ways either they show what they claim too and work or they dont and if they dont they are useless and we need the experts to be honest about it and say they dont.
Its confusing and frustrating to have studied the provided information and listened to the opinions of the experts weigh it against the other sources and our experences and others experences, then get no-no dont do that for using that information/tool.

 

[Garry H (Cut Nut)]

StormRider it would be good if we could give you and everyone a simple answer to say this diamond is 97 out of 100 quality and this other one is 98 out of 100. But there are too many variables in the diamonds, the measurement systems, the people buying them, what their friends will think, wether size is weight, or size is diameter, do you like fire or brightness, do you wear glasses, can you focus less than 12 inches or only more than 16" etc etc.

And just for good measure - here is one of the ray traces that I used to estimate the leakage / return. Even that was not simple - see why I said it was an estimate?

 

[strmrdr]

cut nut:
Im not looking for a 89 out of a 100 system it would be nice but it is too much to expect because the computing power it would take would be huge.
Then just agreeing on the model and fine-tuning it would take years.
Then there would be unexpected results because of something that the model doesn’t take into account and or because light by its nature does unexpected things at times.
Then humans might not be able to separate a 50 from 100 when you’re done.
...................................................................
What Im looking for are the tools accurate enough to be useful or not?
On one hand we are being told yes they are but on the other were being told no they are not.
If they are only useful up to a point where is that point?
...................................................................
As for the ray trace its interesting but not that hard to understand while im rusty at the math behind it the model is easy to see what it is, what’s happening and why its happening,
These days if you know how to interpret the results you don’t necessarily need to know the math because the computer programs do it for you.
When I studied it we had to do the math on a scientific calculator and paper.
While dealing with lasers is not always the same as dealing with broad spectrum light it is close enough that I can understand it.
I have studied cutting diagrams and designed my own cuts and ran them thru ray tracing software to further my knowledge as it applies to gemstones.
I have also read much of the cut study documents here:
http://www.gemology.ru/cut/english/coll_rays.htm
and played with the models available there changing various parameters and seeing if the results are as predicted by what the experts here have said.
For example on question it answered is if there was a difference between a 41 and a 40.9 pavilion angle when the crown angle stayed the same.
The answer as you know is yes.

 

[fire&ice]

I'd just pick the pretty one.

 

[Beth]

Garry the newsletter link is not working for me.

 

[valeria101]

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On 4/3/2004 4:50:27 PM Cut Nut wrote:

'Tip: Diamonds with leakage look brighter and more firey in high open backed ring settings, so light can get in the back.'

----------------

Is THIS the explanation why girls are supposed to endure those #!@&*^&@!~! high settings suspending diamonds in the wind ????

Oh well... good to have it here for ref.

Ray trace... scores looking like 'diamond GRE'. How complicated does this have to get ?! Joke aside: does it matter if only a minority of buyers understand what is valuable about the stones they purchase? Impenetrable info just means more room for lack of disclosure. And it does not have to come from you, the makers and promoters of the cut model and grading system: all you need is one nice fellow telling you "all this is tooo complicated - my word/rule of thumb/ 'eye' is just as good and the price is XX% better". The more arcane the 'truth', the more room for better told, imperfect info is to defeat the purpose of the perfect-but-too-complicated-for-words model.

Just disregard this if I am not clear. Just practicing

 

[Serg]

My map is for total losses( Leakage is part of total losses)

 

[pqcollectibles]

----------------
On 4/4/2004 1:05:43 AM niceice wrote:

----------------
On 4/3/2004 12:19:49 PM strmrdr wrote:

That brings us back to trusting the vendor, lets say we find 3 diamonds and 3 people we trust say theirs are top .1% ers then what?
To go further lets say I talk to Brian the cutter, Rhino and niceice and they each have 2 diamonds what they say are top-notch diamonds close in price/clarity/color to the other vendor’s offerings.
I trust all of them to point me in the right direction and each of these diamonds will be top notch so how do I decide which diamond is the best one for me?----------------

You know the funny thing about this is that Brian, Jonathan and ourselves are so precise in our selection process that we really feel that it's not a matter of which one of us has the better diamond in terms of visual performance, we think they're all essentially the same and many of the gemologists seem to agree when they're sitting their staring at stones from each of us that have been sent over on behalf of a client who is willing to pay for a multi-stone evaluation... And by 'we' the reference is being made by Robin and Todd, not the two of us and Brian and Jonathan, we're not trying to speak for them. The deciding factor is usually a combination of clarity / color / carat weight and price... We kind of think that the decision to purchase from one of us over the other isn't really a matter of quality, we all offer an extremely similar and very precise product... Some days it really just comes down to which one of us happens to have the diamond the customer is seeking because our holdings are different from each other in terms of specific stones on any given day... Brian might have a 1.42 carat puppy when we don't while Jonathan has a 1.37 to offer and we only have a 1.62 or something and Brian ends up selling the stone to the customer that day because his stone is closer to what the customer wants - which happens to be a 1.50 carat stone while the budget won't quite reach that far... And a few days later, Jonathan might have the right stone while Brian and Robin and I don't... And then it will be our turn, make sense?

----------------

There is a lot of truth in that statement. There have been several buyers post similar stories. They previewed diamonds from different Vendors. All the contenders were beautiful and any one could have been "the one". The buyers' selection was based on price point, or size, or price point and size.

 

[valeria101]

No.. my true addictuion is not browsing PS ! Is making charts

The one below contains the exact same data as the colorfull plot (bar the background colors). The initial chart seems to show the same function on two different scales, so one can determine the relation between scales (as below). What does it mean?

Well... diamonds do not leave pitch black shadows, some light does go through. So there is a technical light return between 10% and 50% from round cut diamonds. Actually I am quite surprised at how high this goes!!!! We are talking about one of the most transparent materials, actually... Quite amazing what those facets do

And people see them and appreciate diamonds' sparke using bilogically imperfect tools and judgement... so one would recognize that diamonds with reflcet about half the light throuwn at them are erally exceptionally 'sparkling' objects overall. For these, subjectively, there is only 10% 'room for improvement' - so they top the subjective scale at nearly 90%.

Actually, one could turn the subjective scale in an index (like the Bscope has) or whatever. It is always good to leave the top and bottom of the scale for people to wander "what's up (or down) there" - since absolute positions are tricky to define.

Hope this little interpretation is right, and not completely missplaced.

 

[Iiro]

A week ago I thought I had a good idea.

Can we call all the red virtual facets reflectors, and red and white anti-reflectors?

Total loss of light = related to antireflectors
Total return of light = related to reflectors

??

 

[Garry H (Cut Nut)]

Or red = windows on the crown and mirrors on the pavilion
White = entry windows on the crown, exit windows on the pavilion and possibly mirrors on the crown.
pink = crown windows and partial pavilion windows and mirrors (like 2 way mirrors)

 

[niceice]

----------------
On 4/4/2004 1:40:10 AM strmrdr wrote:


Im getting a little frustrated.
The 'experts' have given us the hca,ideal-scope,aga charts, and a bunch of other tools and tutorials on how to use them ,then when we use them to seperate diamonds that are very close we get told to not be so picky about the readings/images/angles/ratings/what evers.
----------------

We've NEVER supported the use of these various marketing tools, in fact, those of you who are familiar with our posts may recall that we're usually quite leery of them. At best, it could be said that we politely tolerate their existance. We can't think of a single marketing tool related to diamonds that we support other than the Sarin / OGI machine and a digital camera for the purpose of taking clarity photographs... But then again, we're also known for being a bit cynical. We don't go for all the hype and we're slow to jump on the band wagon because we don't want to be on it when the wheel falls off and it's going kind of fast... The challenge as we see it is that there are no absolutes when it comes to determining the light return of a natural crystal "off of the numbers" and while there is some consistency of what can be seen through the various scopes, each diamond kind of has it's own variations. And you do realize that the purpose of our web site has always been to educate and not so much to sell, OMG, the layout of the site alone should tell you that. It doesn't have your commercial, corporate slick, "I'm a shopping cart" buy here kind of feel... It's not that we couldn't make it look like every one of our competitors, but that's not our purpose, it never was. Sure, we sell a lot of diamonds via the internet, but in truth, it surprises us each and every day. Systems? Oh, we have our systems for buying diamonds, but we're not much for all the light return calculators, scopes, etc. other than to have them on hand to answer the questions that all of you need answered in the middle of the night, but those of you who have talked with us in person - have we ever given a single one of you the impression that we rely on those things as part of OUR buying process? No, we think not.

This is not to say that we don't find the development of these tools to be interesting... And it is not to say that we don't think that some of these tools have merit... And it is not to say that at some point in the future we won't use these tools as part of our selection process WHEN we think that they have arrived so to speak. But for now, they are just interesting experiments that we watch with wonder and amazement - usually because we're amazed that so many people blindly rely upon these tools as if they were "absolute indicators of brilliance, dispersion and scintillation" - sorry we're too skeptical for that ourselves...

So leave us out of the "expert" circle as far as this stuff goes friends because if we're even near the circle, we're definitely sitting along the outside of it.

To the question at hand, Yes Garry, it seems that we posted our comments at the same time and we see what you're saying, but then again, your examples are pased upon the results of a computerized simulation and you already know from many of our personal discussions to this regard how we feel about computerized simulations no matter how interesting we find Sergey's work to be... And actual pictures of the diamond as taken through your ideal scope wouldn't address the question because those would show the diamond as interpreted through your scope which has the angle we initially specified...

The QUESTION is... Would the "leakage" be different if the angle of the pink reflective surface within the scope were different? And this can only be answered by the development of several different scopes, each with different angles for the reflective surface... We're thinking out loud and don't know the answer ourselves, but it seems logical to us that if the angle of the pink reflective surface were changed even slightly, that the entire pattern of light return and leakage would change accordingly. It's simple common sense. And the concept can be tested in theory simply by trying different desk lamps on a desk in a dark room and watching how the circumferance of light changes with the angle of each individual lamp shade...

We are NOT saying that the Ideal Scope / Fire Scope / SymmetriScope / Light Scope, etc. doesn't work... Not at all... What we are asking is what would be the effect if the angle of the reflective surface was changed?

We feel that part of the frustration experienced by Strmrdr is the simple fact that a lot of the relevations and technical discussions had within our industry are being aired out for the public to assimilate here on Price Scope, that in itself is a two edged sword... A lot of our discussions are interpreted to be truth, when in fact, most of it is theory... Don't mistake the evolution of the technical aspects of our industry to be absolutes when 99.9% of it is just theory - most of which is in the early development stages... People, we're going to look back on these threads in five years and wonder how we could have believed a lot of this... Those of you following the discussions of trade members should do so with the understanding that many of us are simply thinking and theorizing out loud... This same concept applies to the proportions that diamonds are cut to and the cutting technology itself, the diamonds we sold five years ago are not as precise as the diamonds we sell today, the diamonds we sell today (hopefully) will not be as precise as the diamonds we sell tomorrow... Our industry is constantly evolving, the ideas being discussed today lead to the development of the equipment that will provide answers in the future.

 

[strmrdr]

Robin & Todd,
I was/am well aware of your stance on them and never considered you in the circle pushing these tools.
I included you with Brian and Rhino because you made a good third and have a different way of selling than they do and you are on my trusted people list.
I appreciate your candor on the issues that come up here.

You hit on a large part of my frustration I love theory and the pure theory discussion on here are of major interest to me that isn’t the problem.
Where the frustration comes in is when that theory is used as marketing.
Honestly I don’t like marketing and am highly suspicious of it.
That is what Im trying to sort out is it marketing or useful.

Robin & Todd, I pretty much know your stance on the following questions and thank you for it.
………………………
………………………
My question to everyone else remains are these tools: marketing, theory used as marketing, or fact?
Explain please.

If fact then why can’t they be used harshly to separate diamonds?
Cross vendor there is a lighting issue I know.

If all these tools just separate out the top 2% 5% 10% or whatever diamonds what do we use to make the final selection?
Bringing a dozen diamonds in to look at isn’t a practical answer.
Its easy if a vendor you trust has all the stones left after the separation just have them discuss them with you and use their eyes and knowledge to make the selection.
But when the diamonds are at multiple dealers then what?

 

[valeria101]

Some of this chat is actually going beyond the purpose of the tools at hand: since when doubts and marketing go hand in hand? Until today I have been rather convinced that the inside of that little scope acts as a diffuse (indirect) light source - so it's shape does not matter as loong as it is not comparable in size with the diamond in it

Have you tried to stab raw rice beans Strmdr? No idea what tools you've got in the kitchen, but I would need some darn small and swift knife to do that trick.

Most of these tools here are treating the little diamond prisms like the respective rice beans. The error of the cut is just not good enough. Next step... You may say i'm nuts (ok...), 'cause it is not very useful to cut beans, right? Well, neither it is to split diamond hairs.

Hope this makes sense, without sounding insulting. I am new to the story after all.

 

[valeria101]

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On 4/4/2004 10:29:15 PM strmrdr wrote:



If all these tools just separate out the top 2% 5% 10% or whatever diamonds what do we use to make the final selection?

----------------

Hm... this is weird.

Remember the quantum theory of light? It might help, but not with the current models of diamond optics here. By using ray-trace they all rule out subatomic phenomena

There might be some good news ahead though: given sufficient particle acceleration you might be able to actually count those... if you don't mind badly irradiated diamonds, that is.

(ok particle accelerators are NOT suitable for diamond grading - just a joke).