Measuring Diamond Angles/Proportions in Settings

[bluelotus]

Hello all,
I recently purchased a very nice 1920s men's ring with a diamond that is original to the setting. I know that color is impossible to assess without removing the diamond from the setting but I am curious to know if it is possible to piece together specs on the stone. I am particularly interested in knowing crown and pavilion angles. . . I would assume that one could fairly accurately estimate lower girdle facets and star facets. It seems to me that there are enough surfaces exposed that one could extrapolate if the crown angle were measurable. Reading Gilbertson's "American Cut" has piqued my interest in the history of cuts and I find it interesting to see what appears to be a fully formed modern round brilliant set in the 1920s. The stone was purchased in Europe (or England) and set in the ring stateside.

 

[John P]

Approximate crown details: 56% table, 36-37°CA, 44-46% stars, 16.5 CH (±).

The image has a bit of off-axis tilt so these aren't concrete but they're in the ballpark. The size, tilt and reflections in the image prevent meaningful pavilion estimations. If you have a larger image, perfectly level, made in even diffused lighting I can estimate more. You did a nice job of taking the image with no darkness created by the camera lens, but some obstruction is desirable in order to gauge PD/PA. An image modeled after the mag images the popular PS sellers make would be ideal.

 

[bluelotus]

Hi John, thanks for the information so far. I'll do my best to get a straight on shot and post it. I am an architect by training and figured I could trace a scanned image in AutoCad but I figured there must be other ways to do this. More later!

 

[bluelotus]

I am having trouble uploading from my phone right now but will try again later. In the meantime this is one that I posted in a another thread and looks to be better. This is kind of hard to photograph with an iphone.

 

[bluelotus]

Maybe this one is better?

 

[bluelotus]

And this one because the colors are so cool!

I have read, with much interest, the threads on optical symmetry and the quest for the kind of perfection that the H&A diamonds embody.
I wonder to what extent the cutters of the early modern brilliants were making conscious decisions about symmetry (or lack thereof). How much was a product of the limitations of measuring technology and how much might have simply been the pursuit of a specific visual style?

I have enjoyed learning about symmetry by way of dreamer's early American ideal and wonder to what extent the symmetry exhibited in such early stones was a happy bi-product of accurate cutting or if the strong presence of arrows was intentional. Many of the early modern stones I have seen exhibit the kind of controlled randomness that my stone shows and I guess I am wondering if this was an intentional departure from the earlier cutting styles where the structure and composition of the facets was more easily discernible.

 

[bluelotus]

For reference, here is Dreamer's stone:



Dreamer, I hope you don't mind that I have reposted your image!

 

[pyramid]

Would this be a Firey Ideal Cut? It is very beautiful, love the colors.

 

[bluelotus]

FIC? That is what I am thinking and will be curious to learn more. The ring came with a couple appraisals that were done over time which state the depth in the range of 57% to 59.3%. The girdle has been described as thin to very thin. This all described without removing the stone from the setting.

 

[John P]

Maybe this one is better?

On my phone that looks good. I'll apply it once I get home. Currently in ATT Stadium in Arlington for some Saturday HS football.

 

[pyramid]

Maybe more people could afford diamonds so more production and less time to spend cutting them so accurately? Interesting thought though, I have never seen it mentioned here. Be interested to see what those in the trade think.

 

[John P]

[attachment=0]I wonder to what extent the cutters of the early modern brilliants were making conscious decisions about symmetry (or lack thereof).

Quick reply: One indicator is application of the very term "symmetry". You're using it in a way that reaches all the way into 3D Optical Precision (and resultant patterning like H&A). But to this day the term "symmetry" as labs use it does not take 3D precision into account.

For old cutting, and even now, "symmetry" only refers to facet shape and meet points on the 2D diamond surface, and alignment/twist of crown relative to pavilion. It takes an incredibly severe amount of distortion/variance before a 10X "symmetry" grade is influenced by anything involving 3D precision.

With that said, even the oldest drawings of diamond wire-frames arguably implied symmetry/precision goals in all three dimensions. Whenever I pick up one of the large glass diamond paperweights at industry trade shows it was made with 3D precision. The default in diamond design software, and the simulations used in video commercials have perfect 3D precision.

The reason 3D precision was not considered in 1950s grading, and still not graded by USA labs is simply because diamond is HARD. Even today, trying to meet tolerances of tenths of degrees and achieve ideal standards for meet points/polish is intensely difficult. Adding a 3D precision component demands enhanced planning, more time, more expense of weight, better tools and better labor skill. In short, demanding it would cost producers a lot more money & manpower and hugely complicate traditional manufacture.

That said, as a trade we continue to progress. It was not long ago that there wasn't even a cut grade for rounds at GIA (2006). Now cut standards have become stricter worldwide. I would also note that our youngest market, China, does demand 3D precision grading, since cut considerations have been in their paradigm since day 1 (not so in the west). It's one reason that Chow Tai Fook recently acquired Hearts On Fire. The market there has more awareness/demand for that cut component.

 

[Serg]

[attachment=0]I wonder to what extent the cutters of the early modern brilliants were making conscious decisions about symmetry (or lack thereof).

Quick reply: One indicator is application of the very term "symmetry". You're using it in a way that reaches all the way into 3D Optical Precision (and resultant patterning like H&A). But to this day the term "symmetry" as labs use it does not take 3D precision into account.

For old cutting, and even now, "symmetry" only refers to facet shape and meet points on the 2D diamond surface, and alignment/twist of crown relative to pavilion. It takes an incredibly severe amount of distortion/variance before a 10X "symmetry" grade is influenced by anything involving 3D precision.

With that said, even the oldest drawings of diamond wire-frames arguably implied symmetry/precision goals in all three dimensions. Whenever I pick up one of the large glass diamond paperweights at industry trade shows it was made with 3D precision. The default in diamond design software, and the simulations used in video commercials have perfect 3D precision.

The reason 3D precision was not considered in 1950s grading, and still not graded by USA labs is simply because diamond is HARD. Even today, trying to meet tolerances of tenths of degrees and achieve ideal standards for meet points/polish is intensely difficult. Adding a 3D precision component demands enhanced planning, more time, more expense of weight, better tools and better labor skill. In short, demanding it would cost producers a lot more money & manpower and hugely complicate traditional manufacture.

That said, as a trade we continue to progress. It was not long ago that there wasn't even a cut grade for rounds at GIA (2006). Now cut standards have become stricter worldwide. I would also note that our youngest market, China, does demand 3D precision grading, since cut considerations have been in their paradigm since day 1 (not so in the west). It's one reason that Chow Tai Fook recently acquired Hearts On Fire. The market there has more awareness/demand for that cut component.

There were not real technical possibility to grade 3D symmetry in 1950s.
3D symmetry grade system does not block any production. limitations depends from tolerance. you are free to increase tolerance.
but developing the reasonable 3D symmetry grade system is real challenge even if you have precise scan 3D model.

there is huge difference between 3D symmetry grade system and just any symmetry grade system based on 3D model.

 

[bluelotus]

John,
I never really considered the challenge of cutting the diamond material as one of the factors. I have never actually seen cutters at work but will remedy that someday!

I think I understand what you are saying about 3D symmetry - that it's not enough for symmetry to exist in facets and meet points projected onto a 2D plane but that each facet should be reflected exactly by its opposing facet relative to the x and y axes. I see now where the challenge lies and how difficult it must have been 100 years ago.

There is still the question of the intentionality of visual style in early modern brilliants. Perhaps the splintery randomness was not only a way of circumventing the difficulty of strict 3D symmetry but but also a conscious aesthetic choice?

 

[bluelotus]

Serge,
I think I understand you to mean that, after a point, there are increasingly minute criteria for 3D symmetry that make it difficult to quantify?

 

[bluelotus]

John,
What software do you use to generate the wireframes?

 

[Serg]

Serge,
I think I understand you to mean that, after a point, there are increasingly minute criteria for 3D symmetry that make it difficult to quantify?

There is not good correlation between 3D symmetry and Optical symmetry, between 3D Symmetry and Visual( minor) symmetry ( facet junctions,.)

simplest examples are culet, table tilt or shift . it significantly destroy 3D symmetry but have low impact for Optical symmetry .

3D symmetry instrument is more important for cutters to achieve Plan( reference cut) with minimal weight loss .
Optical symmetry is more important for consumers .

Girdle symmetry is important for all participants of diamond market ( but it is possible to grade in 2D)

 

[John P]

John,
What software do you use to generate the wireframes?

DiamCalc by Octonus. It's Serg's company.

http://www.octonus.ru/oct/products/3dcalc/standard/

Ran out of time. The wife is redeeming weekend-coupons with me But this is on my to-do for later.

Also, good discussion above. I have several thoughts.

 

[bluelotus]

Look forward to hearing back!

 

[bluelotus]

Bump! John, do share if you have a chance!

 

[John P]

Found some time today.

Previous:

Approximate crown details: 56% table, 36-37°CA, 44-46% stars, 16.5 CH (±).

Less tilt in this image. The numbers above still apply. The new photo shows lower half lengths circa 77-78%. Without a known obstruction metric table reflection isn't clear (it's how we gauge p-depth) but I'd estimate PA at around 41 degrees. Some predictable human variation is evident and logical, per the brillianteerer's assignment, but I find the diamond well-fashioned.

 

[John P]

Image:

 

[bluelotus]

John,
Interesting. Thanks for taking a look at this. I was particularly eager to understand how the proportions on this diamond might relate to Tolkowsky's range of proportions given the fact that the diamond was purchased in London or Antwerp during the 1920s. It certainly has the look of an early ideal to me. I was curious too to see how it might fare running the numbers in the HCA but it seems that there are too many unknowns to do that yet.

I don't have much experience looking at the super ideal diamonds IRL being cut today but growing up in the 1970s/80s I saw alot of early to mid-century stones and this one reminds me of that look. We had a family friend who became our adopted grandmother who had been a Ziegfeld girl during the 20s and who had some fantastically beautiful diamonds. The broad flashes and high contrast on this stone remind me of Marilyn's jewelry if my memory serves me. In any event, the more I wear the ring the more I love the cut on the stone. . . it is wildly fiery and prismatic in some light, bright and sparkly in much lighting at work, and it looks amazing in the dappled under-tree diffuse light. Tends to have higher contrast than other modern stones that I have seen recently but I don't know if this observation really means anything in relation to the super ideals.

ETA: The whole question of visual style and intentionality has to do with having seen alot of the those splintery modern stones and wondering if their lack of perfect symmetry with high contrast was more planned than is assumed.

 

[bluelotus]

John,
What kind of photo would allow you to estimate pavilion angle?
Just got the ring back from the appraiser this week who described the stone as an early Tolk ideal. Diameter 8.45, depth is 4.97.
When I play around with different CA and PA combos on the HCA seems to fall between the ranges for TIC and FIC. Interesting. Seems to confirm tendency to be very fiery and have high contrast.

 

[bluelotus]

I love how this stone can be confirmed as an early precursor of the contemporary super ideals. A cool example of diamond cutting history!