Critical Analysis - Interesting Stone

[MamaBee]

You can tell the difference between 5.86x5.86mm and 5.85x5.87mm by the naked eye alone?

Is your name Clarke Kent?

 

[John P]

Crafted by Infinity are probably the tightest cutters of MRBs - they only cut around 1000 a year and spend more time than others (AIUI) on ensuring facet accuracy and alignment in order to deliver improved light performance.

There are ongoing discussions around whether this creates a visible difference compared to other, 'normal' SuperIdeal stones. Some have said Yes after viewing them side-by-side, others have said No.

CBI would certainly argue that improved consistency of facet groups yields better light performance, I'm sure (@John Pollard would be able to confirm) but how much does one facet being 0.1degree off from the rest actually affect light return/performance?

Thanks for asking @OoohShiny . There is a short answer and a long answer.

@yssie nailed the shorrt answer: GIGO. Scanner measurements are just not precise enough to permit debate about 0.1 degree between facets. Standard error is wider, and that's when the scanner is properly calibrated.

In fact I have a question for veteran members of the community. Who knows how these 3D diamond scans are actually made?

The longer answer is very basic. Precision-cutting predates scan technology. The very small percentage of operations who are committed to cutting diamonds to higher levels of 3D optical precision never used scanners to guide their efforts. And we do not use scanners to assess the end product. They are simply not accurate enough.

I'll work to find time to elaborate on this in the next days.

 

[Jnana]

Mr. Pollard,

All fair, but assuming you had more accurate measurements, what would your personal opinion be regarding this analysis:

I would prefer to see the 5.85-5.87 size be more symmetrical, 5.86-5.86.
The crown angle is a little open, a tighter 34.5 would be an improvement to this stone
I would take the Lower Girdle down to 75 or 76, fatten up the arrows
To me 61.4% depth is too deep, shave off 0.2%

I am more interested in discussing the perfect shaped diamond even if we cannot measure at that level easily.

 

[yssie]

@Jnana, I suggest these threads as starting points:

https://www.pricescope.com/community/threads/true-hearts-technical-discussion.91276/
https://www.pricescope.com/community/threads/azimuth-shift-yaw.33257/
https://www.pricescope.com/community/threads/yaw-angst.33691/

I think you will find many of your questions addressed, and perhaps they will give you fodder for more in-depth discussion.

1. Those who’ve already encountered those links will note that I left out the truly angsty thread - that was deliberate. I think my second and third links cover the highlights without the drama.
2. Scanners are discussed in some detail.

 

[OoohShiny]

Thanks for asking @OoohShiny . There is a short answer and a long answer.

@yssie nailed the shorrt answer: GIGO. Scanner measurements are just not precise enough to permit debate about 0.1 degree between facets. Standard error is wider, and that's when the scanner is properly calibrated.

In fact I have a question for veteran members of the community. Who knows how these 3D diamond scans are actually made?

The longer answer is very basic. Precision-cutting predates scan technology. The very small percentage of operations who are committed to cutting diamonds to higher levels of 3D optical precision never used scanners to guide their efforts. And we do not use scanners to assess the end product. They are simply not accurate enough.

I'll work to find time to elaborate on this in the next days.

Thank you for your reply and future elaboration, John!

I do recall Yoram saying the Octavia can only be taken so far on machine measurements before the human eye has to take over!

Am I correct in thinking that the diamonds are laser-scanned to measure them? I might be misinterpreting pictures of equipment I've seen, plus assuming it's laser-based because lasers are fricking cool lol

Mr. Pollard,

All fair, but assuming you had more accurate measurements, what would your personal opinion be regarding this analysis:

I would prefer to see the 5.85-5.87 size be more symmetrical, 5.86-5.86.
The crown angle is a little open, a tighter 34.5 would be an improvement to this stone
I would take the Lower Girdle down to 75 or 76, fatten up the arrows
To me 61.4% depth is too deep, shave off 0.2%

I am more interested in discussing the perfect shaped diamond even if we cannot measure at that level easily.

What is your motivation for asking the question?
Are you in the trade and looking to develop a line of ultra-tight-tolerance MRBs?

The question as asked assumes there is only one 'perfect' way to cut a diamond, so any given facet group measurement *must* have a given set of other facet group measurements, and that all other ways are a compromise. I would, instead, propose that all variations of diamond cuts are a compromise - how the outcome does or doesn't meet your expectations depends entirely on your expectations.

For example, if you wanted 60/60-style white-light return but the rough only enabled an OEC-style high crown and tiny table stone to be produced, it might be a 'perfect' OEC but would be a terrible 60/60, regardless of facet group consistency. And if said OEC had ultra-consistent facet groups, it might be 'perfect' in terms of facet accuracy but might fall far short of that abstract concept 'character', which is so prevalant in wonky vintage stones cut by eye on 'primitive' equipment.

How would we determine 'perfect' anyway? Is it your decision? An industry-wide agreement? A scanner-based light-return-based grading system, a la AGS? A public opinion survey, a la Tolkowsky?

 

[skypie]

I actually think a 34.475 crown angle is better. And I prefer 75.5 LGFs and a depth of 61.8125.

Mr. Pollard,

All fair, but assuming you had more accurate measurements, what would your personal opinion be regarding this analysis:

I would prefer to see the 5.85-5.87 size be more symmetrical, 5.86-5.86.
The crown angle is a little open, a tighter 34.5 would be an improvement to this stone
I would take the Lower Girdle down to 75 or 76, fatten up the arrows
To me 61.4% depth is too deep, shave off 0.2%

I am more interested in discussing the perfect shaped diamond even if we cannot measure at that level easily.

 

[sledge]

I actually think a 34.475 crown angle is better. And I prefer 75.5 LGFs and a depth of 61.8125.

Can you explain EXACTLY why those are your preferences, and what benefit my eyes would appreciate from using them?

 

[Jnana]

More pics

My preferences are driven by light return. I am not so convinced that there are many different shaped diamonds that are all just as good as each other although that seems to underlie the logic of many of the comments.

 

[sledge]

Those pics are tiny. And the "more pics" doesn't take me anywhere.

 

[skypie]

I don't think anyone is arguing with the logic that differently shaped diamonds have different light performance. It's just that you can't accurately measure or perceive such differences when you're talking about hundredths of a degree or a millimeter. Thus further discussion of such imperceptible differences is merely academic and not at all practical IRL, IMHO.

 

[OoohShiny]

More pics

My preferences are driven by light return. I am not so convinced that there are many different shaped diamonds that are all just as good as each other although that seems to underlie the logic of many of the comments.

Pass me my magnifying glass


Can you define 'good'?

 

[lovedogs]

I don't think anyone is arguing with the logic that differently shaped diamonds have different light performance. It's just that you can't accurately measure or perceive such differences when you're talking about hundredths of a degree or a millimeter. Thus further discussion of such imperceptible differences is merely academic and not at all practical IRL, IMHO.

This.