Let's discuss Crown Height's role in Step Cuts

[chrono]

I used to think that a high crown in step cuts in a must but not anymore. I once had an EC that had great stats on paper with table and depth under 65%, medium girdle, VG polish and symmetry and the loveliest steps and a fantastic crown (12%), but it does not sparkle as well as my new EC which also has great stats on paper, other than a lower crown when viewed from the side. It isn't flat but is certainly not as high as I would prefer aesthetically. The first EC was purchase locally without ASET and the second is from JA with ASET.

It leads me to 2 conclusions:
1. Great stats on paper is insufficient (which I'm sure most of us already know)
2. A high crown height doesn't guarantee good dispersion

What I'd like to know more about is how crown height plays into light performance. How can a great performing EC still get away with a 10% crown height and why doesn't a 12% and higher crown height "save" a mediocre EC.

 

[woofmama]

Thank you for starting this thread Chrono. I feel I didn't understand crown hgt when I purchased my EC. Overall I'm happy with it, it's a lovely bright performer but I never asked for crown hgt and now wish I had. Definate learning curve here. Can't add to this discussion but looking forward to soaking up some knowledge.

 

[diamondseeker2006]

I am sure Karl can come and explain it all! I just happen to think a higher crown contributes to the overall beauty of the stone, and there are many other factors that cause good light performance. A great stone will have the whole package, but it doesn't mean that others won't be pretty. I didn't know anything scientific about crown height when I bought my asscher, but I knew it had a good ASET and a nice crown at 13.2%.

 

[Karl_K]

A high crown means nothing is the angles and locations of the facets do not work well together.
A low crowned stone can whip a high crown stone if it has better matched angles and the facets are in better locations.

Why a high crown is better when the angles and locations are good is a much harder question to answer and it gets quickly into self-promotion for me.
The short answer is more and snappier dispersion and more off angle light gathering ability.
The long answer involves virtual facets and is very complex.

 

[Karl_K]

Also in an EC it makes less difference than an SE because you will always have the large center virtual facets on an EC, but a higher crown and smaller table does make them snappier or change faster with tilt.
With ECs it is mostly pass/fail. Either it is too flat they tend to glassy or its ok and it looks good.
However that is assuming that the angles and locations of the facets match up.

 

[bgray]

also -and I dont want anyone to assume i am generalizing--when you have a large table you tend to have a low crown height. deep stones tend to have higher crowns but not always. so if certain components fall into place in cutting the rest often do as well. it would be less likely to have well cut facets, an ideal table and depth and a very low crown....never say never but i have looked at a lot of stones....

 

[diagem]

A high crown means nothing is the angles and locations of the facets do not work well together.

Hummm, what about the sculpture effect and not to mention exterior light reflections?

 

[Rockdiamond]

Really interesting discussion- thanks for starting it Chrono!!
Speaking as one who sees value in many different styles of cutting, I find that the internet has materially changed the way consumers look at diamonds, and Emerald Cuts are a great example.
Here's how: If consumers want to buy based on limited info ( like on the web), a higher crown seems to make more sense, from a scientific viewpoint.

Karl's Octavia exploits the high crown better than just about any other cut I've ever seen

So, consumers that do research will naturally find a higher crown attractive.
The reality of the way diamonds use light- light performance- is sometimes counter intuitive.
Cutters have found ways to make a shallow crown look far more "steppy" than common sense might dictate.
A large table, low crown can actually emphasize the steps ( facet breaks) on the pavilion ( the bottom)

The same science that makes high crowns look essential, can also lead us to the conclusion that high crowns have a down side- which is spread. In some cases ( not all) the higher crown holds weight that might otherwise be spread across the finger.
Therefore, it seems to make a lot of sense to explore both. Higher crown, smaller tabled, emerald cuts, and also stones with larger tables, lower crowns, greater spread, and excellent light performance IMO.

 

[Mayk]

Love this topic...thank you Chrono!!!

 

[Karl_K]

A high crown means nothing is the angles and locations of the facets do not work well together.

Hummm, what about the sculpture effect and not to mention exterior light reflections?

That should have read:
A high crown means nothing IF the angles and locations of the facets do not work well together.
Those are both additional advantages of a high crown, but if the facets don't work well together they aren't going to save a dud.

 

[Karl_K]

Cutters have found ways to make a shallow crown look far more "steppy" than common sense might dictate.
A large table, low crown can actually emphasize the steps ( facet breaks) on the pavilion ( the bottom)

I call those classic emerald cuts as many were cut at the time the diamond saw was invented, and many before out of flats. They are pretty but a little sleepy in scintillation. Some people love them.
Before that some crowns were higher, then in the more moderns cuts they moved back up but not as far as some before the diamond saw. I call these modern EC cuts.
The very high crown ECs I call antique style, they are very rare today.

With SE there are other factors that come into play that makes a bigger difference with a higher crown but again a shallower crown better matched can beat a higher crown where everything is not as well matched.

 

[Karl_K]

Classic EC 73T 9CH. Virtual facets in Red, notice they are pretty much all large to very large.

Looks bright:

 

[Karl_K]

What I can't show you in static images is the dwell time for changes in virtual facets hence flashes with tilt.
It is like: bright bright bright bright dark dark dark bright bright bright dark dark dark repeat.
Where with the same tilt a smaller table and higher crown could be like:
bright bright dark dark bright bright dark dark repeat.
In other words it flashes more times for the same amount of tilt.

 

[chrono]

Karl,
What does 73T 9CH mean? 73% table and 9% crown height?

The way I read it is that crown height is irrelevant if the angles do not work together. However, if given the choice, once the angles are found to be optimal, then a higher crown height is preferred for a quicker and flashier scintillation. My next question now will involve interpreting the ASET. How can it be possible to have a good ASET (lots of red with some green) if the crown isn't high? The ASET is supposed to translate / predict how the EC handles or reflects light, both direct and around it. My ASET is impressive in that there is a lot of red with some green, yet the crown is surprisingly low. I did not have a Sarin done but it is definitely around 10% by my eye ball guesstimate. Table is 63% so it isn't glassy and it is quite a fireball. I suppose it means that the scintillation would be quicker if the crown height is higher?

 

[chrono]

David,
I've noticed that a large tabled EC with a low crown seems far less flashy. I think the appreciation of steppiness is insufficient because the purpose of any diamond is to sparkle its little heart out. Is there really such a thing as a spready large tabled EC with a low crown that is considered to have high light performance?

It also makes sense that a square step cut will have slightly different requirements to be a great performer. It seems such a shame to have so few well cut step cut diamonds. Light performance aside, few have depths under 65% and many have thick girdles, leading to stones that face up so small relative to other shapes. Worse yet, it is not easy to find something with VG symmetry and polish on top of all that. I prefer very small tables as well and anything under 60% is a rarity.

 

[Karl_K]

Karl,
What does 73T 9CH mean? 73% table and 9% crown height?

Correct

The way I read it is that crown height is irrelevant if the angles do not work together. However, if given the choice, once the angles are found to be optimal, then a higher crown height is preferred for a quicker and flashier scintillation. My next question now will involve interpreting the ASET. How can it be possible to have a good ASET (lots of red with some green) if the crown isn't high?
Yes, it is actually easier to get more red with a shallower crown

The ASET is supposed to translate / predict how the EC handles or reflects light, both direct and around it.
ASET only covers potential brightness by showing where it is drawing light. It shows little about "life" or scintillation(I believe that scintillation is not the only factor in a lively stone but that's another thread)

My ASET is impressive in that there is a lot of red with some green, yet the crown is surprisingly low.
not surprised

I did not have a Sarin done but it is definitely around 10% by my eye ball guesstimate. Table is 63% so it isn't glassy and it is quite a fireball. I suppose it means that the scintillation would be quicker if the crown height is higher?

Yes in general, if the angles and placement were well matched.

 

[Karl_K]

Here is the ASET for the virtual example used above.
I literally designed it in 10 seconds, I could fine tune it for even more red in about 5 min.

 

[chrono]

I admit to being surprised that it is easier to get more red to show with a shallower crown. If that is the case, then the ASET is a good tool but not the perfect tool nor should it be the only tool used to predict light performance of step cuts.

 

[woofmama]

Here's the ASET from my ec that I currently have set in my Sholdt setting:
Here are the specs Carat weight: 1.11
Cut: Excellent
Color: K
Clarity: VVS1
Certificate: GIA

Depth: 63.3%
Table: 65.0%
Polish: Excellent
Symmetry: Very Good
Girdle: Slightly thick
Culet: None
Fluorescence: None
Measurements: 6.24*5.71*3.62

The steps light up beautifully and it is amazingly bright but does have a large table and a very low crown. So based on the discussion here what would think the perfomance would be? I'm trying to learn the correct way to judge step cut stones. Great thread!

 

[Karl_K]

I admit to being surprised that it is easier to get more red to show with a shallower crown. If that is the case, then the ASET is a good tool but not the perfect tool nor should it be the only tool used to predict light performance of step cuts.

Bingo

 

[Karl_K]

Here's the ASET from my ec that I currently have set in my Sholdt setting:
Here are the specs Carat weight: 1.11
Cut: Excellent
Color: K
Clarity: VVS1
Certificate: GIA

Depth: 63.3%
Table: 65.0%
Polish: Excellent
Symmetry: Very Good
Girdle: Slightly thick
Culet: None
Fluorescence: None
Measurements: 6.24*5.71*3.62

The steps light up beautifully and it is amazingly bright but does have a large table and a very low crown. So based on the discussion here what would think the perfomance would be? I'm trying to learn the correct way to judge step cut stones. Great thread!

I remember that one.
Did you get the CH from JA?
If not can I see a clear side shot if you have one? 65%t isn't large, its borderline.

 

[woofmama]

Karl,
What does 73T 9CH mean? 73% table and 9% crown height?

Correct

The way I read it is that crown height is irrelevant if the angles do not work together. However, if given the choice, once the angles are found to be optimal, then a higher crown height is preferred for a quicker and flashier scintillation. My next question now will involve interpreting the ASET. How can it be possible to have a good ASET (lots of red with some green) if the crown isn't high?
Yes, it is actually easier to get more red with a shallower crown

The ASET is supposed to translate / predict how the EC handles or reflects light, both direct and around it.
ASET only covers potential brightness by showing where it is drawing light. It shows little about "life" or scintillation(I believe that scintillation is not the only factor in a lively stone but that's another thread)

My ASET is impressive in that there is a lot of red with some green, yet the crown is surprisingly low.
not surprised

I did not have a Sarin done but it is definitely around 10% by my eye ball guesstimate. Table is 63% so it isn't glassy and it is quite a fireball. I suppose it means that the scintillation would be quicker if the crown height is higher?

Yes in general, if the angles and placement were well matched.

So this is reflected in the ASET I posted of my stone? If it had a higher crown I would have more scintillation?

 

[woofmama]

Here's the ASET from my ec that I currently have set in my Sholdt setting:
Here are the specs Carat weight: 1.11
Cut: Excellent
Color: K
Clarity: VVS1
Certificate: GIA

Depth: 63.3%
Table: 65.0%
Polish: Excellent
Symmetry: Very Good
Girdle: Slightly thick
Culet: None
Fluorescence: None
Measurements: 6.24*5.71*3.62

The steps light up beautifully and it is amazingly bright but does have a large table and a very low crown. So based on the discussion here what would think the perfomance would be? I'm trying to learn the correct way to judge step cut stones. Great thread!

I remember that one.
Did you get the CH from JA?
If not can I see a clear side shot if you have one? 65%t isn't large, its borderline.

Karl sorry I'm not sure what you're asking me. What do you mean by Did you get the CH from JA? And yes I'll post a side shot, give me a moment to find a decent pic.

 

[woofmama]

Silly me.....You're asking if I got the crown height from JA. No I didn't. back when I bought this I didn't know to even ask that question. So I really have no idea. Here's a pic of the profile:

 

[Karl_K]

Same crown as above, make the p2 big, p3 small. Set the p2 to 41 degrees, lots of red. Sucky stone with little life.....

 

[Karl_K]

Silly me.....You're asking if I got the crown height from JA. No I didn't. back when I bought this I didn't know to even ask that question. So I really have no idea. Here's a pic of the profile:

Cant tell for sure from the pic a close up would help. But it doesn't look flat it is at least 10%.

 

[woofmama]

Silly me.....You're asking if I got the crown height from JA. No I didn't. back when I bought this I didn't know to even ask that question. So I really have no idea. Here's a pic of the profile:

Cant tell for sure from the pic a close up would help. But it doesn't look flat it is at least 10%.

Thank you Karl for taking your time to help educate on this topic. I don't have any great pics available and no time today to try and get one. Perhaps tomorrow I can revisit this topic. Also hoping that I'll have ASET on the octagon asscher I found.

 

[Rockdiamond]

David,
I've noticed that a large tabled EC with a low crown seems far less flashy. I think the appreciation of steppiness is insufficient because the purpose of any diamond is to sparkle its little heart out. Is there really such a thing as a spready large tabled EC with a low crown that is considered to have high light performance?

It also makes sense that a square step cut will have slightly different requirements to be a great performer. It seems such a shame to have so few well cut step cut diamonds. Light performance aside, few have depths under 65% and many have thick girdles, leading to stones that face up so small relative to other shapes. Worse yet, it is not easy to find something with VG symmetry and polish on top of all that. I prefer very small tables as well and anything under 60% is a rarity.

Hi guys,
This discussion seems to prove my point that on the web scientific likelihoods are more appealing/ easier to grasp or confirm than hands on assessment.
I agree that there's a scientific likelihood that a high crown can have better light performance, however we also agree that high crown small table does not guarantee a good performer.
Also implicit in this statement, is that a shallow crown emerald cut can be a far better performer than another stone with a high crown.
I have found that some shallow crown stones with larger tables- even into the low '70's possess tremendous flash, and scintillation.
When considering light performance, does the spread come into anyone's calculations? I consider the size of a stone in relation to others of the same weight to be quite important.
Shallow stones can often have greater spread than higher crowned, smaller tabled stones.


The aspect of hands on assessment that is most valuable also makes it very difficult- especially if we are talking about subjective assessments, such as light performance.
But with step cut stones, I don't believe there's ever going to be any quantifiable assessment method other than eyeballs. There's so many more variables than considering a round diamond.
The exact placement of facet breaks on step cuts is not quantified on any gemological report, yet IMO that has a more direct relationship with how an emerald cut performs than Crown height and or Table size unto itself. Same thing for corner size- which has a HUGE impact on light performance.
Chrono- the low crowned stones you've seen that were less flashy: were these stones you've seen in person, or online? Were the stones set or loose?

 

[chrono]

Woofmama,
Your stone isn't flat topped at all! I think the crown height is definitely there, not super pillowly the way antique OMCs are but the profile looks fine.

My EC
T64 D63.1

Is anyone willing to hazard a guess as to the crown height of the EC shown below? It is strange that it looks sort of flattish in person, yet seems decently high in the pictures. I wonder if it is because the horizontal step "lines" are confusing the eye.

 

[chrono]

David,
Scientific explanation is easier to understand because it is repeatable, predictable and provable. With a hands on assessment, unless the viewer is experienced and knows what to look for, most people do not understand what they are looking at and / or have no ideal basis for comparison.

For me, spread is an added bonus to getting a bigger look but it means little if it doesn't show sufficient flash, sparkle and all that good stuff. When shopping for my stone, I eliminated all stones with a depth of over 65%. I am aware that I am limiting my options greatly but spread is important to me. That said, after getting my small pool, I then went on to the other cut specifications such as table, and etc. My original pool has now decreased by nearly 90%. From here, I now look at the appearance of the remaining ECs to look at the cut, steps, potential brightness and etc to just a handful which now undergo ASET testing. I would never pass over a smaller but flashy fiery snappy EC for something spreadier but mediocre.

Is light performance truly subjective if it can be scientifically explained? It is quantifiable but a PITA to capture all the variables as they are numerous and varied. I do agree with you though that the combination or relationship of the the facets have a greater performance impact than merely crown height or table size alone.

The less flashy ECs I viewed were in person, mostly loose.