Table size %'s

[diagem]

Just going to put this here...
Any answers and/or opinions would be appreciated.

With all the technological tools available, why aren't Lab's calling the true surface area measurements between table size and face-up size?

 

[AdaBeta27]

pi r squared vs. pies are round? Jewelry buying should be easy. Less math, more fun. I don't know exactly how they derive that table % now. But it's easy for me to remember I want a 55% - 56% table on a RB, and I at least don't think I need to know anything more about the table. But that's from a consumer's point of view.

 

[diagem]

pi r squared vs. pies are round? Jewelry buying should be easy. Less math, more fun. I don't know exactly how they derive that table % now. But it's easy for me to remember I want a 55% - 56% table on a RB, and I at least don't think I need to know anything more about the table. But that's from a consumer's point of view.

Thanks AdaBeta27,

I understand and respect your view on this, but I am asking more towards those who do pick the macro numbers associated with 3D proportions.
As far as Gemological standards, with all the toolings available why not offer the real measurements?

Just a humble question I guess....

 

[sharonyanddave]

pi r squared vs. pies are round? Jewelry buying should be easy. Less math, more fun. I don't know exactly how they derive that table % now. But it's easy for me to remember I want a 55% - 56% table on a RB, and I at least don't think I need to know anything more about the table. But that's from a consumer's point of view.

Thanks AdaBeta27,

I understand and respect your view on this, but I am asking more towards those who do pick the macro numbers associated with 3D proportions.
As far as Gemological standards, with all the toolings available why not offer the real measurements?

Just a humble question I guess....

I think this has been debated extensively here: https://www.pricescope.com/forum/ro...e-of-spread-in-a-fancy-shape-t139459-150.html

Among the hurdles to your position It would seem Gary H has decided to eliminate the spread field from listings at Pricescope even for Princess and Round. Given that even Pricescope doesn't agree on giving customers this information I highly doubt the labs will do so in the near future.

I would agree with your assertion that surface area in mm squared where obtainable would be informative. Even relating the spread to the same carat weight Tolk Round would be helpful to consumers of all knowledge levels.

Trying to explain to a novice consumer that they should be looking at mm measurements rather than carat weight in Fancy shapes is challenging and has come up twice in the last week or so.

It is even a challenge to explain to someone a 0.6 carat round with Ideal proportions will faceup just about as large as a weight saving 0.7 with a thick girdle and 63% depth.

 

[RADIANTMAN]

I totally agree with Diagem. The weight of a diamond is actually a misleading piece of information if its not accompanied with information about its visible size which is the area of the girdle plane, and there is absolutely no reason why that information can't be included routinely on a lab certificate.

Since the "right" spread for carat weight varies by shape using a round as a baseline the way some have suggested may not be the best approach, but if a total spread number were provided consumers could at least fairly compare diamonds of the same shape.

Is a 1 carat cushion really worth more than a 0.90 that literally is just as big or bigger in spread? Especially if the life is comparable? To some people probably yes and to some no but without that information the consumer can't really get the information they need to make that judgment call for themselves.

 

[sharonyanddave]

It is nice to see at least one brand providing the spread measurements this may be the only way consumers can get this information for fancy shapes. I am curious though how are you calculating that number and how much is it rounded off?

 

[RADIANTMAN]

Diamonds with straight edges like radiants, princesses and emerald cuts are pretty easy to calculate spread for. For a princess its just length x width. For a radiant or emerald cut it's length x width minus the area lost by cutting off the corners (normally around 7%). That's the figure reflected on our certificates. We round to the nearest 0.5%.

The area lost from cutting the corners reduces the spread when the diamond is loose, but since a prong generally goes on the cut corner it has less of an effect on how the diamond will appear when mounted. That means that a 5x5 radiant will appear smaller when loose than a 5 x 5 loose princess, but when mounted the two diamonds will appear pretty much the same size.

Round stones are easy to calculate too - it's just pie r squared. Other rounded edge shapes are tougher but can easily be calculated with modern measuring equipment.

 

[diagem]

While I could agree with a spread factor being added to the grading reports, i do have a problem with the comparisons issue.
Dont see the logic of comparing to rounds (only).

My reason for this thread is more towards the true areas separating crown area & table area of the top portion of the Diamond cut (e.g. the portion above the girdle). I think that knowing how much both areas are from each other can add important information regarding the face-up appearances of the cuts.

For example, if the table percentage is 50% of the crown area (girdle outline = 100%) of a Diamond cut then there could be significant play of light vs. a 70% table in any given cut.

Thats where my objective to this thread lies...

 

[Texas Leaguer]

Visible surface area in my mind is not exactly the same as spread or "area of the girdle plane". It sounds like splitting hairs but two stones with the same outside dimensions, one with a built up crown, would have different surface area. And they could have substantially different optics.

I do like the idea of having additional information about this key factor on the report. Certainly, the calculations could easily be done with the scan info. It would be a question of deciding exactly what calculation would result in the most useful data point.

 

[diagem]

Hi Bryan,

Didn't surprise me you were going to jump ahead (in case you would participate in this thread) on this issue, of course you are 100% correct, surface area includes a 3D factor such as CH and each lgf, star & main including each of their respected facet angle and azimuth and their play of light..., but I believe you are too early, I would like to start with the simple 2D measurements..., real measurements.