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Can you tell anything about cut with just length, width, depth measurements?

DoeEyes

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I'm considering a 0.91ct 6.27mm-6.30mm X 3.75mm. Emailed for the additional measurements for the HCA but just wondering if you can tell anything about the cut from this info (whether it's deep or shallow I guess?)

In full disclosure because I don't want to anger the mods, this particular stone is a lab-grown diamond, but since I am only asking for feedback about cut, and this board has much higher traffic of prosumers, I'm hoping this post can stay here.
 

DoeEyes

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You can at least calculate the depth percentage from the measurements. Approximately 60%. The dimensions indicate a pretty good 'spread'. Beyond that, you can't make any assessments about overall cut quality or faceting precision.
Thanks! I will post again when I get more info.
 

DoeEyes

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Already got a different one but curious what these angles say about this one. Thoughts?

Screenshot_20191207-080949.jpg
 

DoeEyes

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This is what I got when I put it in HCA. Seems good I think?

Screenshot_20191207-081435.png
 
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OoohShiny

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Already got a different one but curious what these angles say about this one. Thoughts?

Screenshot_20191207-080949.jpg
Looks like a 60/60 stone. 40degree pavilion might be risky in terms of leakage, and don't forget that will be a rounded/averaged number as well.
 

OoohShiny

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John Pollard

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Was the crown angle a typo?
It looks like 39.1 was entered instead of 35.1. Given how shallow the pavilion angle is the HCA result should not change appreciably. The FIC classification will change, though.

For the record, these proportions are predicted as AGS 5 in light performance due to the likelihood of drawing obstruction (darkness caused by the reflection of the observer) at close viewing distances. Some here might classify it as a great pendant stone, as it will be very bright from the distances at which pendants are usually viewed.

In full disclosure because I don't want to anger the mods, this particular stone is a lab-grown diamond, but since I am only asking for feedback about cut, and this board has much higher traffic of prosumers, I'm hoping this post can stay here.
I'd vote for that. It's an opportunity to illustrate why you will encounter shallower angles than usual (like to 40 PA here) in CVD-produced laboratory grown diamonds. The material grows vertically, so the rough is essentially cubic.



(Courtesy SoniCVD - cubes at top right are annealed)

Shallower plans typically benefit cut-geometries in terms of brightness, but many will risk drawing abundant shadow when viewed close. It's the polar-opposite of the 'steep-deep' proliferation seen in natural diamond production where the diamond can be dark due to deep geometries which permit windowing / leakage.
 

John Pollard

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Thanks! What does contrasty mean?
Contrast refers to the diamond's pattern of light and dark areas seen in normal viewing conditions.

I presume @flyingpig was referencing the fact that shallow proportions sets draw more darkness than ideal or deep sets do. In the image below (from the similar example @flyingpig found and linked) you can see the black lens of the camera reflected rather strongly in some lower halves, as well as the eight pavilion mains, along with dark "paddling" seen in some of the bezel facets.

If the camera was moved a few inches farther away the dark areas would be less severe.

ps-shallow-6060.jpg
 

flyingpig

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See @John Pollard 's response.

To add, compare these two stones. One is ideal cut, the other is similar to yours.
Notice more darkness in the shallow stone with 40.0 PA, both under the table and next to arrowheads. Also, notice the deeper black arrows


If the camera was moved a few inches farther away the dark areas would be less severe.
/QUOTE]
Bluenile already positions their camera farther away from the diamonds, than other vendors (CBI, JA, WF, VC). The fact that you see this much contrast in the BN video suggests that the darkness can be very persistent even from a full arm length.

Listen to the inventor of HCA, Garry himself. Starts at 2:42
 
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Serg

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Contrast refers to the diamond's pattern of light and dark areas seen in normal viewing conditions.

I presume @flyingpig was referencing the fact that shallow proportions sets draw more darkness than ideal or deep sets do. In the image below (from the similar example @flyingpig found and linked) you can see the black lens of the camera reflected rather strongly in some lower halves, as well as the eight pavilion mains, along with dark "paddling" seen in some of the bezel facets.

If the camera was moved a few inches farther away the dark areas would be less severe.

ps-shallow-6060.jpg
Shallow diamonds like Cr35.5 P40 are dark from any distance because outgoing ray is parallel to incoming ray. It is similar to nailhead diamonds with very deep pavilion.
Diamonds with slightly deep pavilion (P34.5 P41.1=40.7+0.4 degree) have much more Life than diamonds with slightly shallow pavilion ( P34.5 P40.3=40.7-0.4)
Screenshot 2019-12-08 11.37.07.png
 

AV_

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@Serg What changes if you move the lower & upper girdle length into the 'old cut' territory?
 

OoohShiny

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Awesome posts, @John Pollard, @Serg and @flyingpig :))

That video is great, and the Octonus diagrams are really interesting!

I am slightly conflicted / confused, though :???:

The HCA/IS/ASET recommendations would be to avoid deeper pavilions (because of the potential dark ring under the table when viewed head-on), but the Octonus diagrams suggest that going deeper on the pavilion can create some really wide dispersion fans (and hence fire).

Is if therefore fair / correct to say that these things are just one of the balancing acts / trade-offs between the different cut variations?


(On a side note, I am surprised a 40degree pavilion can get under 2 on the HCA tool - probably a lack of understanding on my part!)
 

Serg

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Awesome posts, @John Pollard, @Serg and @flyingpig :))

That video is great, and the Octonus diagrams are really interesting!

I am slightly conflicted / confused, though :???:

The HCA/IS/ASET recommendations would be to avoid deeper pavilions (because of the potential dark ring under the table when viewed head-on), but the Octonus diagrams suggest that going deeper on the pavilion can create some really wide dispersion fans (and hence fire).

Is if therefore fair / correct to say that these things are just one of the balancing acts / trade-offs between the different cut variations?


(On a side note, I am surprised a 40degree pavilion can get under 2 on the HCA tool - probably a lack of understanding on my part!)
@OoohShiny ,
1) I do not recommend diamonds with strong leakage zones as P41.6-42 degree /Cr34.5.
2) Between shingly deeper and Shallow diamonds, I strongly prefer slightly deeper diamonds as P41.2Cr34.5
Garry prefers slightly shallow diamonds.
In next year I am going to cut samples with different pavilion angles to direct blind comparison during our Cut Performance workshops.
 

John Pollard

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I am slightly conflicted / confused, though :???:

The HCA/IS/ASET recommendations would be to avoid deeper pavilions (because of the potential dark ring under the table when viewed head-on), but the Octonus diagrams suggest that going deeper on the pavilion can create some really wide dispersion fans (and hence fire).
Not in every case. Remember the ASET renderings show brightness, contrast-areas & leakage, but not dispersion. Some predictions can be made, but "wide dispersive fans" is diamond specific. There are indeed 2D proportions sets which help, but seeing more fire also depends on the geometry of main v half-facets, C/P height and optical precision. Remember also, the sims above are perfect wire-frames. The wide world of manufactured diamonds are not.

(On a side note, I am surprised a 40degree pavilion can get under 2 on the HCA tool - probably a lack of understanding on my part!)
The shallow side of the HCA has some human preference built in. Garry included some combos which draw more obstruction due to the trade offs you mentioned. He is very forthcoming about that, indicating that certain (low) scores may be more suitable for pendants or earrings.
 

John Pollard

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Bluenile already positions their camera farther away from the diamonds, than other vendors (CBI, JA, WF, VC). The fact that you see this much contrast in the BN video suggests that the darkness can be very persistent even from a full arm length.
Thank you @flyingpig. I hadn't realized that about BN. One small correction, we are not a vendor. But the images we used to provide to vendors selling the diamonds we craft were taken at closer range. GCAL is now providing images for HPD, also at closer range.
 

OoohShiny

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@OoohShiny ,
1) I do not recommend diamonds with strong leakage zones as P41.6-42 degree /Cr34.5.

2) Between shingly deeper and Shallow diamonds, I strongly prefer slightly deeper diamonds as P41.2Cr34.5

Garry prefers slightly shallow diamonds.
Thank you for offering your views! :)

I find it interesting how Trade members have differing viewpoints and different preferences, but I think that adds to the benefits of Pricescope - a wide range of views is important for ensuring consideration of all angles (pun intended :D) in a discussion :))

In next year I am going to cut samples with different pavilion angles to direct blind comparison during our Cut Performance workshops.
I did not realise you run workshops! They sound like a lot of fun as well as being educational.



Not in every case. Remember the ASET renderings show brightness, contrast-areas & leakage, but not dispersion. Some predictions can be made, but "wide dispersive fans" is diamond specific. There are indeed 2D proportions sets which help, but seeing more fire also depends on the geometry of main v half-facets, C/P height and optical precision. Remember also, the sims above are perfect wire-frames. The wide world of manufactured diamonds are not.
Good points! It is hard to remember everything we should be considering when looking at diamonds - it makes my head hurt... :???: lol

I guess that individual scanning of individual cut diamonds is what is needed to ascertain exact geometries and light performance - or at least very accurate assessment of rough and modelling of desired cutting outcomes, taking into consideration the fact that the rough might not play ball, in order to try to deliver cutter/customer preferences (which Serg is doing)??

The shallow side of the HCA has some human preference built in. Garry included some combos which draw more obstruction due to the trade offs you mentioned. He is very forthcoming about that, indicating that certain (low) scores may be more suitable for pendants or earrings.
The HCA tool sounds like Spock - a great mix of logic and emotion :D lol
 

Rhino

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@Serg What changes if you move the lower & upper girdle length into the 'old cut' territory?
A complete game changer. The HCA is designed around modern round brilliant cuts whose lower half facets are generally cut with with lengths greater than 75% for the most part.

When you extend the lower halves (lgf) to 75%+ a great deal of the reflections under the table are from those facets which will be read in good scoring HCA diamonds as "red" with the "blue" coming from the pavilion mains.

One of the primary differences in OEC diamonds is their shorter lgf, generally lower than 70% and their reflections consume 99% if not 100% of the reflections happening under the table. So a great scoring HCA OEC will show predominatly blue under the table which would make an OEC extremely dark under the table. No good. :)

LGF angles in Ideal cut rounds are generally around the 42 degree zone (red in modern ideal cuts under the table) so in OEC bringing the pavilion mains over 41 degrees and approaching 42 will make the mains red in ASET and remove the obstruction. HCA is not designed for and does not work for OEC.

In the graphic below we have a Tolkowsky Ideal Cut in the upper left. The best possible ASET for a round brilliant cut. Take the same exact diamond and make it's lower havles 60% makes the reflections under the table predominately blue (upper right). :( Change the pavilion angles to 41.6 they go from blue to red. :) The bottom right is further alterations and tweaking. :D :razz:

ASETEVO.jpg
 
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AV_

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It is near midnight here, else I would be thanking more at length! @Rhino
 

OoohShiny

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It is near midnight here, else I would be thanking more at length! @Rhino
Likewise here - I need my brain to be working properly to think about the angles so it will have to wait until tomorrow! :lol:
 

OoohShiny

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I'm just coming back to this thread because I now (finally!) have a laptop on which the Cutwise site works :)

And OMG - it is amazing. :shock:

Total 100% credit to Serg for creating a site with such an overwhelming wealth of information!! :clap:


I was mainly prompted to post because I was browsing stones and came across this 0.61ct F VS1, which caused me to think about the discussions further up the page re: Fire/dispersion:


Length × Width5.382 mm5.368 mm
Total Height63.14%3.395 mm
Table56.38%3.031 mm
Crown Angle34.11°
Crown Height14.75%0.793 mm
Pavilion Angle41.36°
Pavilion Depth43.84%2.357 mm
Girdle4.54%0.244 mm
Culet0.4%0.022 mm
Diameter Ratio1.003

It seems to show a ring of leakage under the table when head-on in ASET black, but the moving ASET-black seems to show good light return from those pavilion facets as soon as it starts tilting.

On the HCA it doesn't do well:

Cut Advisor Score 3.7


FactorGrade
Light Return:Very Good
Fire:Good
Scintillation:Good
Spread:Good
HCA Score :3.7 - Very Good - Worth buying if the price is right

and only gets a 'Good' for Fire... yet on Cutwise, it is graded as 'Outstanding' for Fire.


This has me totally confused :???: lol

Is it just a personal-taste difference between Serg and Garry?

Is Cutwise highlighting a limitation of current head-on-viewing-only ASET use?

Is it a SuperIdeal vs A.N.Other cutting style?
 

Serg

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@OoohShiny

re:Is Cutwise highlighting a limitation of current head-on-viewing-only ASET use?

Such diamonds( RBC P41.3Cr34.5) highlight limitation of Static Cyclops observation.
Btw Cutwise scores do not use any information about cut proportions, they use only movies to calculate fire and brilliancy,
 

OoohShiny

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@OoohShiny

re:Is Cutwise highlighting a limitation of current head-on-viewing-only ASET use?

Such diamonds( RBC P41.3Cr34.5) highlight limitation of Static Cyclops observation.
Btw Cutwise scores do not use any information about cut proportions, they use only movies to calculate fire and brilliancy,
Thank you for the conformation, Serg :)

It means another thing to consider if/when looking at options! :D

Nothing seems simple when it comes to diamonds... :lol: lol
 
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