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

[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.

Bingo

That being the case, how would one go about shopping for a well cut emerald cut or asscher cut stone? Let's presume the eyes are not well trained and the buyer is open to both online and in person purchase.

 

[Karl_K]

Is light performance truly subjective if it can be scientifically explained?
Both, what people like is subjective but science can be used to give it to them and explain why a stone acts the way it does.

It is quantifiable but a PITA to capture all the variables as they are numerous and varied.
To be honest designing step cuts both on the wheel and virtually, that just looks good comes up a lot. Then one tries and figure out why it does what they like and how to add more or modify it. Everything is a compromise in one way or another.

 

[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

That being the case, how would one go about shopping for a well cut emerald cut or asscher cut stone? Let's presume the eyes are not well trained and the buyer is open to both online and in person purchase.

I have to be up early for a job and am in the middle of a job tonight so don't have time for an in depth answer.
The short answer: online: get as much information as possible, if possible use a vendor with a solid reputation for picking them, make sure you have a good return policy and view it in as many lighting conditions as possible during the return period.
In person: view as many as possible in as many lighting conditions as possible and get a good return policy for an evaluation in your own environment.

There are a few things I suggest looking for but not enough time tonight.

 

[chrono]

Karl,
I appreciate your response and the wait for a proper response will be worth it. Thank you. Also, when you get the chance, would you hazard the crown height of my EC at the end of Page 1?

 

[diagem]

I could agree to a negative spread factor when it comes to the more common/generic EC's which usually entails a combination of low CH (around 8-5%), large table (>70%) and a extremely deep pavilion depth (53-49% +/-). That's where most of the hidden extra weight is located out of sight usually in the interior of the jewel (e.g. setting). But when the viewer has the posibility to enjoy the visual of a "correctly applied" higher crown height complimented by a proportionally sized table and pavilion depth the spread factor is not at all negative, it becomes a positive IMO.

 

[bgray]

Karl,
I appreciate your response and the wait for a proper response will be worth it. Thank you. Also, when you get the chance, would you hazard the crown height of my EC at the end of Page 1?

9 /10?

 

[Rockdiamond]

Is light performance truly subjective if it can be scientifically explained?
Both, what people like is subjective but science can be used to give it to them and explain why a stone acts the way it does.

It is quantifiable but a PITA to capture all the variables as they are numerous and varied.
To be honest designing step cuts both on the wheel and virtually, that just looks good comes up a lot. Then one tries and figure out why it does what they like and how to add more or modify it. Everything is a compromise in one way or another.

There are two Manners of assessing something. One would be objective. The diamonds weight is a good example of an objective measurement
Put it on a scale and you get the carat weight.
ALL Assessment of Diamond's cut is subjective.
In the case of round diamonds, it is a much more narrow parameter that is agreed-upon to be subjectively pretty.
We don't even have those agreed-upon parameters with step cut diamonds.
The methods of measuring a diamond may be scientific, but the methods of assessing it's beauty(Light performance) are totally subjective.

 

[chrono]

Let me try to word this clearer this way: light reflection is measurable and can be scientifically mapped, explained and measured. Whether one defines a certain range as beautiful or not is subjective but I am sure no one ever complained step cuts sparkled too much.

Opinions?

 

[bgray]

Let me try to word this clearer this way: light reflection is measurable and can be scientifically mapped, explained and measured. Whether one defines a certain range as beautiful or not is subjective but I am sure no one ever complained step cuts sparkled too much.

Opinions?

yes and no-- IMO. David makes some good points. light reflection is measureable but not the quality of the light and the overall performance because you cannot separate the shape and other nuanced variables from the light return. you do in fact have the major variable in step cuts completely absent as a factor in round brilliants. is it white, is it rainbow hued, do the complex variations of the corner facets add something completely unquantifiable?

 

[Karl_K]

One part of the science of high crowns.

Take a pen and hold it at the bottom and wave it back and forth, for a small rotation at the base the tip of the pen travels a large distance and faster then the base where you are holding it.
Now hold the pen 1 inch from tip and repeat. The tip travels a much shorter distance and at a slower speed.
The same thing happens with the table of a high and low crowned diamond.
More and faster movement for the same rotation means more scintillation events for any given rotation.
Advantage high crown.

 

[Karl_K]

1: pleasing outline
2: pleasing static patterns, bright?
3: nice looking ASET
4: as you move it does it flash with small rotation? Good.
5: are there large areas that stay bright or dark and don't flash with small rotation? not so good.
6: repeat the flash test in lots and lots of lighting conditions.

4,5,6 are where video can be a big help when shopping online.

 

[Rockdiamond]

Hi Chrono: Current technology does allow measurement of light reflection head on.
An element missing from this equation is the introduction of movement, which then becomes scintillation ( sparkle)
To my knowledge, a means of measurement of this crucial aspect has not been agreed upon.
Personally, I can't imagine a methodology that will work, but I could not have imagined the iPhone either

So, at this point, sparkle is totally a judgment call.

Having said all that, I'm going to start using ASET to correlate how shallow top emerald cut that I find attractive look in the reflector.

I could agree to a negative spread factor when it comes to the more common/generic EC's which usually entails a combination of low CH (around 8-5%), large table (>70%) and a extremely deep pavilion depth (53-49% +/-). That's where most of the hidden extra weight is located out of sight usually in the interior of the jewel (e.g. setting). But when the viewer has the posibility to enjoy the visual of a "correctly applied" higher crown height complimented by a proportionally sized table and pavilion depth the spread factor is not at all negative, it becomes a positive IMO.

Totally agreed that the bulk of emerald cuts on the market today have huge bellies most advantageous for holding onto weight.
Some of these might even look quite nice in terms of sparkle, and steppiness- but I don't want a 1ct stone that looks like a .80ct.

But there's another category where you have shallow crown and shallower pavilion. So there's no hidden weight. Plus, since there are three of even four facet breaks on the pavilion, smart cutters can adjust the angels to encourage a lot of movement of light.
No question, like all stones of exceptional cut, they are rare in the market.

 

[Karl_K]

In person and video a well cut EC and SE you can clearly see the play of light across the stone as it is slowly rotated and the virtual facets light up. The best ones you can literally walk the light across the stone and back firing virtual facets at will.

 

[Rockdiamond]

1: pleasing outline
2: pleasing static patterns, bright?
3: nice looking ASET
4: as you move it does it flash with small rotation? Good.
5: are there large areas that stay bright or dark and don't flash with small rotation? not so good.
6: repeat the flash test in lots and lots of lighting conditions.

4,5,6 are where video can be a big help when shopping online.

+1

 

[chrono]

I am so glad to have started this thread and have so many of you chime in with your experience and opinions. It has given me a better understanding of how to evaluate step cuts and a better appreciation for it too.

Now then.....only Bgray has dared to guess the CH of my EC to be around the 9 to 10% height. Any other takers?

 

[Karl_K]

I am so glad to have started this thread and have so many of you chime in with your experience and opinions. It has given me a better understanding of how to evaluate step cuts and a better appreciation for it too.

Now then.....only Bgray has dared to guess the CH of my EC to be around the 9 to 10% height. Any other takers?

With the tilt and rotation a reasonably accurate number is not possible.
I would say at least 10%.

 

[chrono]

At least 10% CH is good enough for me. I like the descriptor of being able to see the each facet light up, one after another across the EC, then back again as it rotates. It is very easy to understand, evaluate and know that this is the ideal to aim for.