Recommended Proportions

[John Pollard]

This is an absolutely beautiful update to the educational section! Kudos and cheers!

Thank you @DejaWiz . Kudos and cheers to you and your clever cohorts - and all who weighed in. This was a community project.

Diamond Proportions

Diamond Proportions

The physics of light-behavior within a diamond are reliably consistent, which means proportions measurements can be useful.

www.pricescope.com

 

[Garry H (Cut Nut)]

You did good John

 

[DejaWiz]

@John Pollard question about the rounding:

For heights/depths rounding (pavilion, overall, crown), is GIA, IGI, and GCAL to the nearest 5% or 0.5%?

 

[prs]

Adding those Lower Half Lengths to Garry's chart might do more harm than good. My guess is that whilst your average consumers might be able to understand CA and PA, most of them will have never heard of the "Lower Halves".

Will that "Lower Halves" row actually tell them anything useful, or will it just confuse them? AGS specify LHL to the nearest 1% and only the super ideal vendors use AGS. All the diamonds outside the super ideal range will come with GIA certs, and GIA round LHL to the nearest 5%. This renders the "Lower Halves" row pretty much useless for GIA diamonds.

 

[John Pollard]

@John Pollard question about the rounding:

For heights/depths rounding (pavilion, overall, crown), is GIA, IGI, and GCAL to the nearest 5% or 0.5%?

Nearest 0.5% - actually nearest 0.1% for total depth. Good catch, thank you.

I needed to update that table anyway: IGI is reporting CA/PA with no rounding, and table to 0.5%.

Diamond Proportions

The physics of light-behavior within a diamond are reliably consistent, which means proportions measurements can be useful.

www.pricescope.com

 

[Mlh]

Nearest 0.5% - actually nearest 0.1% for total depth. Good catch, thank you.

I needed to update that table anyway: IGI is reporting CA/PA with no rounding, and table to 0.5%.

Diamond Proportions

The physics of light-behavior within a diamond are reliably consistent, which means proportions measurements can be useful.

www.pricescope.com

I think putting the lgf is terrific! Thank you for that @John Pollard !!

 

[Karl_K]

I think putting the lgf is terrific! Thank you for that @John Pollard !!

If we are going to include extreme combinations then we needed lgf% there is a loud voice on PS atm for larger arrows aka shorter lower halves and with some combos that is not the right answer.
Everything is a trade off and it reaches a point with pretty much every parameter where the trade off tips away from something.

 

[lovedogs]

If we are going to include extreme combinations then we needed lgf% there is a loud voice on PS atm for larger arrows aka shorter lower halves and with some combos that is not the right answer.
Everything is a trade off and it reaches a point with pretty much every parameter where the trade off tips away from something.

Sorry If I'm partially responsible for the weird love of large arrows. I try to be clear that it's just my personal preference.

 

[rungirl]

Should the "Less Bright"/"Brighter" terms be reversed on that arrow at the bottom of the chart? I thought the right side had more fire and less brightness, and the left side the opposite.

 

[John Pollard]

Adding those Lower Half Lengths to Garry's chart might do more harm than good. My guess is that whilst your average consumers might be able to understand CA and PA, most of them will have never heard of the "Lower Halves".

Will that "Lower Halves" row actually tell them anything useful, or will it just confuse them? AGS specify LHL to the nearest 1% and only the super ideal vendors use AGS. All the diamonds outside the super ideal range will come with GIA certs, and GIA round LHL to the nearest 5%. This renders the "Lower Halves" row pretty much useless for GIA diamonds.

@prs - your comments are very logical. In the interest of being thorough we considered all facet groups. You probably know that, absent painting/digging (which should be penalized), upper half angles and star % choices will have negligible influence on the general visual tendencies predicted.

Lower halves are another matter. For one, given the PriceScope community's appetite (noted by Karl), but also because they are influential.

While technically classified as a "minor" facet group, the LHs are "majority shareholders" of the pavilion. There are 16 LH facets (vs. 8 pavilion mains).

The wireframe below is modeled at 77% LH length. As that number increases these majority shareholders occupy even more of the total pavilion surface.


Specific to your observations:

On the broad Visual Tendencies chart: We gave some non-rounded guidance for #nerds, but worked with lab rounding in mind to keep controls in place for outliers. That's why FB starts at 77% and MF at 78%... #nerds may find those examples. Those using rounded reports will only see 75% (not recommended) or 80%, which will be in range.



On the Member Recommended range, which already stipulates 75-80% - we got even more specific.



I hope it's useful info.

 

[Karl_K]

Should the "Less Bright"/"Brighter" terms be reversed on that arrow at the bottom of the chart? I thought the right side had more fire and less brightness, and the left side the opposite.

yes the wording is reversed but the graphic is correct.
It wii be fixed soon.
Thank you

 

[John Pollard]

Fixed now. Thank you @rungirl .

Keep the helpful comments coming.

 

[lovedogs]

Should the "Less Bright"/"Brighter" terms be reversed on that arrow at the bottom of the chart? I thought the right side had more fire and less brightness, and the left side the opposite.

Omg ignore me. I was looking at the chart rather than the arrow at the bottom! You are totally correct

 

[rungirl]

So, I have a question about using the chart in conjunction with looking at super ideals. If I wanted to look for a pair of studs and use the left-hand side as guidelines (brighter, less fire, bigger spread, shallower) would it be difficult or even impossible to find those stats in conjunction with a super ideal? I haven't spent a lot of time comparing stats, but when I have looked at super ideals online they seem to fall more to the middle or right side of the chart.

I guess what I'm really asking is this - are super ideal stats mutually exclusive from the stats on the left side of the chart? If so, is there a recommended way to start searching for well-cut studs using those stats on the left side of the chart?

 

[lovedogs]

So, I have a question about using the chart in conjunction with looking at super ideals. If I wanted to look for a pair of studs and use the left-hand side as guidelines (brighter, less fire, bigger spread, shallower) would it be difficult or even impossible to find those stats in conjunction with a super ideal? I haven't spent a lot of time comparing stats, but when I have looked at super ideals online they seem to fall more to the middle or right side of the chart.

I guess what I'm really asking is this - are super ideal stats mutually exclusive from the stats on the left side of the chart? If so, is there a recommended way to start searching for well-cut studs using those stats on the left side of the chart?

ACA diamonds (and super ideals in general) are cut to fall into the middle of the cart (which is ideal for a ring). So you'll have trouble finding any branded super ideal stones that fall on either extremes of the chart above, since they aren't considered ideally cut to most folks.

 

[John Pollard]

I guess what I'm really asking is this - are super ideal stats mutually exclusive from the stats on the left side of the chart?

Correct. The term "ideal" is frequently associated with proportions near Tolkowsky's (modernized) calculation balancing brightness and fire: 56T, 34.5CA, 40.75PA.

It's why the green "All Around" category invokes his name.



The term Super Ideal, as it's commonly interpreted on PriceScope goes a step farther: "A small range of scientifically proven “ideal” proportions which promote balanced brightness, fire, sparkle, and contrast. Beyond those basic proportions, their internal reflections are further fine-tuned to display 3D optical precision (aka Hearts & Arrows), proven in a specialized viewer."

If so, is there a recommended way to start searching for well-cut studs using those stats on the left side of the chart?

The numbers on the Visual Tendencies chart do that for you already, from a basic 2D standpoint. That said, be sure to read the usage notes above and below the chart.

For example: If you're seeking Visual Type "Less Fire, Bright" at 1.00 carat - the extreme end of that range (60T, 31.0CA, 41.5PA) are proportions which will achieve that look if cut consistently.



There will be a trade-off, though. GIA is allergic to shallow proportions sets, so the stone will get GIA VG in cut. It will also become AGS1 due to the reduced fire and potential for obstruction - which is why the PriceScope chart stipulates that range is best for earrings/pendants.

 

[Garry H (Cut Nut)]

Late to the party.
The LGF is important as Karl says - at the extremes.
The Ideal brands do not want to go shallow - for one reason - AGS will ding them. But the now retired Lab Director agreed when he saw my wife's shallow earring vs an ideal proportioned H&A's in the other ear.
So who is right? Me of course!