What makes a diamond ideal/ super ideal?

[cflutist]

I'd guess that 80% of the people on the street had never seen a top ideal cut in their life, so all diamonds would look the same to them.

I think that is a good observation DF because most ladies compliment my 3.01 F-SI1 pear at first. However, I have had 3 jewelers compliment my 2.21 F-SI1 CBI. One of them was a HoF dealer, another sold high end jewelry in Santa Barbara including Patek Philippe watches @Dancing Fire , and another jeweler in Vancouver BC who thought it was an D or E in color.



@John Pollard paid me a surprise visit at an Inn in Half Moon Bay where I got to play with other CBI diamonds. This sure brighten up my day (was in the dumps a month after my craniotomy to remove a brain tumor). It is not every day that one has six CBI diamonds on their fingers.

 

[blingblingdiamond]

Videos!

 

[whitewave]

Very pretty diamond

 

[Winks_Elf]

All diamonds look great under jewelers lights. But a super ideal should be able to perform in almost all lighting conditions. Here are some photos of my 2.21 F-SI1 CBI in a darkened theater on a cruise ship. I still see fire and dispersion.

Can't wait to see my 2.79 F-VS1 CBI on our next cruise, hint, hint @Wink @Winks_Elf

 

[metall]

This thread is fascinating! I feel like I'm about to dive i to a very very deep rabbit hole....but I wanted to reply so I get updates on this!

ETA: I am dumb and looked at flutist's link and there's a totally a CBI showroom by work....now I wonder if a field trip will ruin my current project....

 

[Karl_K]

Still under the weather but here is a start.
ASET does not have great virtual facet resolution. It blurs them together. Computer generated ones have more resolution but as you can see it is far from showing them all. Once you get beyond just discussing overall brightness and mass contrast these details become important. The image shows double reflection virtual facets they are the primary virtual facets in most lighting and common sizes. There are triple and smaller reflection virtual facets that spit it up further, but they are to small to be effective at returning visible light except in very large diamonds or intense spot lighting.

one image below shows a virtual ASET image the other is the double reflection virtual facets created by the interaction of the real facets. Notice how the ASET blends together many of these virtual facets.

 

[Karl_K]

Why are virtual facets important?
Every aspect of diamond performance other than facet glare begins and ends with virtual facets. Each virtual facet draws light from and returns light to a different parts of the environment around it.(they can also draw light from multiple locations and return it to multiple locations) Basically virtual facets it what separates a polished diamond from a mirror.
If you want to stop there and keep it simple,
Precision cutting creates more precise and uniform virtual facets and optical alignment increases their efficiency at returning visible light.
I'm going to catch some flak on that statement because it is grossly over simplified.
Remember what I said about disagreement earlier?
That's all for tonight.

Edit: The most important aspect of diamond performance is always lighting and how clean it is at that moment.
Maybe I should change my saying that the 5 most important things for diamond performance are: cleanliness, lighting,lighting, lighting, lighting.

 

[Karl_K]

The range of physical facet locations and the possible virtual facets is limited by the round brilliant design unlike a step cut all the major facets are joined to each other at meet points in multiple locations. This locks them into position making less possible variations with a reasonable lab symmetry grade.. Shown a wire outline of a mrb and a poor design step cut.

 

[Karl_K]

Just by changing the lower girdle/lower halve actual facets we can vastly change the virtual facets and the look of the diamond.
Images and virtual facets below. See how different virtual facets can vastly change the appearance of a diamond?

 

[Karl_K]

Now we know that large changes in virtual facets can make a large difference in the appearance of a diamond. You will also notice the second one has far fewer virtual facets, therefore it will have far fewer flashes but bigger ones.
In the real world we would change the other angles to get back more smaller virtual facets and add back some "life".

 

[ChristineRose]

If Karl will indulge me, I'd like to add a quick and dirty analogy.

Image a mirror. The light return is strong, but there's only one facet and no sparkle

Now play the child's trick with two facing mirrors. Suddenly two mirrors are an infinite number of mirrors. But the mirrors get increasingly dim as they move "back."

Now imagine a third mirror, and you get even more dim reflections.

Now put in 57 mirrors. That's so many that you'd have to spend a couple of hours just arranging the mirrors to all face each other.

Now the final step is to tweak the 57 mirrors until some of the additional reflections perfectly overlap one another.There's way fewer virtual mirrors now, but those that remain are all brighter. What's more, if you tilt and move the mirrors, you get a cool 3D effect where the virtual images shift and rotate in space.

Now imagine how much work it takes to arrange those 57 mirrors like that, and you'll get some insight into what it takes to bring us these stones. And then change the relative sizes of the mirrors and cut me an AVR.

 

[Karl_K]

ChristineRose!! you rock! that is very good.

 

[John P]

@ChristineRose - You just demonstrated greater understanding than most career jewelers, and crushed the explanation. I'm headed to a training and will use this today - with attribution. Tip of the hat.

 

[Rockdiamond]

Many thanks all for the explanations.
@Rockdiamond, your repeated examples of small Vs large carat for fire is one I've never seen much sense in, a consumer looking to maximise fire will do so with in a budget, so 0.5 Vs 5 carat is not a useful comparison.

To put it in terms of fire/dollar a better example would be 2.7 carat superideal Vs 3 carat ideal/spready diamond. At that level I think superideals probably maximise fire/dollar

Back to the point about fire: What shape or cutting style would you say is best for producing fire?

About the comparison- let's say the 3ct is noticeably larger, yet very slightly less "bright".
How many people will select it because it looks noticeably larger, while the difference in brilliance is very small, or imperceptible?


Again- this is not about knocking the choice of Super Ideal- but rather adding some context. DF is totally correct that many people have not had the opportunity to look for themselves.
A lot of readers simply take it as gospel that they'd choose the super ideal.
Remember that a lot of dealers here on PS really love Super Ideals- that does color the discussion.
Of the two images below, I believe many PS participants would choose the second one

 

[ChristineRose]

Thank you John and Karl!

 

[Karl_K]

Of the two images below, I believe many PS participants would choose the second one

David my post has nothing to with bad or good, it is showing the effect of changing the virtual facets.
Yes there are several people who would choose an oec type stone but that has nothing to do with my post.

 

[OoohShiny]

If Karl will indulge me, I'd like to add a quick and dirty analogy.

Image a mirror. The light return is strong, but there's only one facet and no sparkle

Now play the child's trick with two facing mirrors. Suddenly two mirrors are an infinite number of mirrors. But the mirrors get increasingly dim as they move "back."

Now imagine a third mirror, and you get even more dim reflections.

Now put in 57 mirrors. That's so many that you'd have to spend a couple of hours just arranging the mirrors to all face each other.

Now the final step is to tweak the 57 mirrors until some of the additional reflections perfectly overlap one another.There's way fewer virtual mirrors now, but those that remain are all brighter. What's more, if you tilt and move the mirrors, you get a cool 3D effect where the virtual images shift and rotate in space.

Now imagine how much work it takes to arrange those 57 mirrors like that, and you'll get some insight into what it takes to bring us these stones. And then change the relative sizes of the mirrors and cut me an AVR.

Unnnnnngh

I'm going to have to sleep on that and hope my brain can process it towards a lightbulb moment lol


What we're saying is that the 'mirrors in the mirror' are the virtual facets?

I think I get that, but it's how that translates to a 3D diamond that is hurting my brain lol

I think the simplicity of those ray-tracing diagrams that have been previously posted in other threads is what is confuddling me, because those are simple in>through>out lines. In my brain the 'virtual mirrors' in the example above are because they are directly oppositely aligned, whereas, say, a MRB doesn't have any directly opposite facets that bounce light back and forth??

I'm not sure how much simpler the "layman's" explanation above can get, or even if it can be simplified - I think I just need to do some visualising in my head lol


Thank you for the great post, @ChristineRose!

 

[Karl_K]

OoohShiny, this help? The arrows are on the rays entering the diamond the ones without arrows are the return. Notice the ones that veer off away from the eyes. The less that veer off the more light that can potentially reach the eye.

 

[ChristineRose]

Unnnnnngh

I'm going to have to sleep on that and hope my brain can process it towards a lightbulb moment lol


What we're saying is that the 'mirrors in the mirror' are the virtual facets?

I think I get that, but it's how that translates to a 3D diamond that is hurting my brain lol

I think the simplicity of those ray-tracing diagrams that have been previously posted in other threads is what is confuddling me, because those are simple in>through>out lines. In my brain the 'virtual mirrors' in the example above are because they are directly oppositely aligned, whereas, say, a MRB doesn't have any directly opposite facets that bounce light back and forth??

I'm not sure how much simpler the "layman's" explanation above can get, or even if it can be simplified - I think I just need to do some visualising in my head lol


Thank you for the great post, @ChristineRose!

The mirrors in the mirrors are like the virtual facets, yes.

The obvious way this falls down is that mirrors are opaque on one side. You can still get the inner reflections if the mirrors are angled though--they don't have to face each other.. But the MRB does have facets facing each other. Each facet faces both in and out because facets are not opaque. But just as the light bounces around in the mirror maze creating many reflections of the other facets, light bounces around inside of the diamond, creating reflections of the other facets.

 

[Rockdiamond]

David my post has nothing to with bad or good, it is showing the effect of changing the virtual facets.
Yes there are several people who would choose an oec type stone but that has nothing to do with my post.

Karl- the fatter faceted stone would have greater fire potential, yes?
My point is that discussions of fire where the actual facet size is not touched are incomplete- the same is true if we discuss fire without mentioning that an RBC - even a super ideal- is not the best vehicle for a diamond to convey fire.
This is by no means a knock on round, or super ideal diamonds. But when someone's main goal in light performance is fire, a round diamond will not provide the greatest amount of fire.

 

[Karl_K]

Karl- the fatter faceted stone would have greater fire potential, yes?

No, actually it wouldn't.
The lack of small and med sized virtual facets in that particular combo would result in comprised fire potential in direct spot lighting.

quote from above:
Now we know that large changes in virtual facets can make a large difference in the appearance of a diamond. You will also notice the second one has far fewer virtual facets, therefore it will have far fewer flashes but bigger ones.
In the real world we would change the other angles to get back more smaller virtual facets and add back some "life".

Small tables and high crowns were not just for rough preservation, they added needed small and med virtual facets as well a 3d presence to the stones while improving off axis lighting response.

 

[Rockdiamond]

Karl- maybe we're not speaking of the same thing.
"Flashes", and the prism effect we call fire are not the same. In my experience, when there are larger facets, there's more opportunity for the prism to be visible.
Are you suggesting that an RBC is the best shape to promote the visible prism effect called "fire"?

 

[Karl_K]

Karl- maybe we're not speaking of the same thing.
"Flashes", and the prism effect we call fire are not the same. In my experience, when there are larger facets, there's more opportunity for the prism to be visible.
Are you suggesting that an RBC is the best shape to promote the visible prism effect called "fire"?

David that statement is so stupid it does not deserve an answer.

 

[Rockdiamond]

Thanks Karl, that's a very nice way to forward a discussion.

 

[Karl_K]

back on track.
Now that we know what virtual facets are and what they do lets talk Ideal cut.
In order for the virtual facets to return light to the eye well the actual facets have to be in a compatible relationship with each other.
The most fundamental is the crown/pavilion angle relationship that is the question the HCA score tries to answers with some success but not 100% accuracy, Do they work together?
Then you have the lower girdle/lower halve angle which is just as important,
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

So an ideal cut starts with 2 things, complimentary pavilion and crown angles and lower girdles that work well with them.

 

[Karl_K]

Next to be considered ideal cut it should have a table size that works with the crown,pavilion and lowers angles.
So so far we have:

vs this:



Don't believe anyone if they try and tell you that many people would pick the second over the first seeing them side by side.

 

[Karl_K]

Now there is some debate is an AGS0 60/60 cut an Ideal cut?
By the ags definition it is.
Others put it in a different class reserving the ideal cut title for stones that have smaller tables.
Some will use the term modern ideal cut to separate them from the 60/60 style ideal cuts.
There really is no right answer to that one.

One argument that does not fly at all with me is that ags owns the term ideal cut and they should be the judge of it. It was in common use well before ags started using it.

 

[Karl_K]

So whats left: star length % and upper girdle facets.
Longer star % can open up the center of the diamond a little but on steep crowns it can make the upper girdle facets to steep reducing edge brightness.
Table size also makes a difference as to what star length is to short or to long.

In general it will be from 45%-55% Occasionally out to 65%
In general a shallower crown(34) can get by with longer stars and the steepening of the upper facet angle can be mildly beneficial.
On the other hand steep crowns(35) or large tables can have reduced edge brightness with long upper girdles as they get to steep and do better with shorter star %.
In general 50% is pretty universal.

 

[Karl_K]

Which brings us to lab symmetry or how well the meet points of the facets align and polish.
GIA EX/EX
AGS ID/ID

 

[Karl_K]

Next up is tools for judging cut.
ASET and Ideal scope.
That will have to wait for another day!