"Asscher" carat weight confusing

[MarionC]

I have a 1.2 Square Cut Emerald/Asscher.
When I was looking at upgrades I found that I would really have to go up in carat weight quite a lot to gain even 1mm. So I started plugging measurements in a carat calculator to figure out what what going on and found that my random sample, a 1.5, was smaller in mm measurements than my 1.2.
How can diamonds that have near the same hxwxd measurements be different carat weights?
Both are GIA.

[Meanwhile I came down with the quite rare disease, perhaps never before documented on PS, of "Reverse DDS" and fell in love with my 1.2 again, but still wonder how carat weight works].

 

[RockBrat]

It's the depth. Step cuts and certain other fancy shapes like cushions and radiants are deep stones. So a 2 ct asscher can face up significantly smaller than a 2 ct round. Just as a 1.5 ct asscher can face up the second as a 2ct, etc.

 

[chrono]

It can be hiding weight in the depth, girdle, wide/narrow corners. This is why when shopping for fancies, look at the mm size, not the ct weight.

 

[MarionC]

It can be hiding weight in the depth, girdle, wide/narrow corners. This is why when shopping for fancies, look at the mm size, not the ct weight.

The 1.5 and the 1.2 have almost exactly the same measurements - h,w,d, but the 1.2 is slightly larger in all directions with "medium to slightly thick" in while the 1.5 is "slightly thick" .
My 1.2 has slightly wider corners. So it might be both the girdle and corners. Very helpful!

I just had trouble wrapping my head around the idea of a 1.2 larger than a 1.5. I guess since GIA weighs, not measures, but we are left to interpret by mms. So I am assuming that a lower carat "stop sign" cut Asscher would have pretty much the same visual weight/finger coverage as an Asscher with tiny corners, since basically the width across can be the same for both?
With the calculator, my stone came out up to 1.47, since they can't take corners into account.

thanks for the insight.

 

[Karl_K]

weight does not equal spread in a step cut.
The same mm measurements varying as much as 50% in weight is not uncommon.
Just don't get caught in the trap that more spread is always better because there are some very badly cut spready asschers out there and very few well cut ones.

See the wire outlines here:
https://www.pricescope.com/journal/performance-and-p3-facets-discussion-about-step-cut-diamonds

 

[MarionC]

Thanks, Karl, for the information.
I will continue to read about and study square step-cuts, and perhaps someday take the plunge again.
I was very lucky to find a great asscher after a year of searching, which has resulted in my hesitation to upgrade. OGI gave the stone a top performance prediction and it turned out to be a winner. Sometimes it's good to stop when things are good : )