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Pricescope recommended proportions & the Inverse Crown and Pavilion Relationship

Rockdiamond

Ideal_Rock
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Jan 7, 2009
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8,050
For me, the differences in table/depth/pa/ca are less dramatic overall, then the shortened LGF's ( as compared to how the best cut 60/60's used to look.)
If we were looking at the way diamonds are currently cut, prs is correct- the overlap will be far greater- and I'd fit right in with Karl and Garry and Serg too..
I don't penalize stones for shorter LGF's, if we're speaking cut quality.
But the different look of a slightly larger ( 60%) table, with the longer (80%) LGF creates a look that accentuates different elements of a diamond's beauty. Scintillation versus fire- call it whatever you want. I prefer that look.
And just as I don't penalize a stone for shorter LGF's, nor do I for longer LGF's when it comes to cut quality.
We were a CBI dealer years ago- they are gorgeous diamonds, without a doubt!
So to me, saying the super ideal is cut "better" for everyone is not correct.
 

prs

Brilliant_Rock
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Dec 26, 2017
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989
If it is a cliff then it is a cliff from one side only( shallow diamonds)
it is not a cliff in direction to deep pavilion diamonds .

it is more looks as mountain range in Sweetline direction with many different and nice pikes depends from LGF, table , star, painting variations.
Also you may find other type of beauty in steep /deep direction Screenshot 2020-02-05 12.24.47.png
Sergey, thank you so much for your reply. I'm learning it's a lot more complicated than just getting the CA and PA right. I believe GIA do provide LGF and star so maybe they too can be factored into the HCA at some point.

However, based on what I'm learning here, it does seem he most important thing is to get the CA and PA right first. Following thru on my idea to have three categories of HCA recommended diamonds, I wonder if we might use your Sweetline (SW) diagram as a basis for defining those categories. With diamonds that fall along the SW called potentially Ideal, diamonds that fall on either side of the SW called Superior, and diamonds that fall into the "deeper pavilion" area called Excellent. This is what I have in mind:

MRB Cut Sweetline 2.jpg

To be honest I've no idea if I've labelled the diagram correctly, hopefully those more expert would be kind enough to comment.
 
Last edited:

Serg

Ideal_Rock
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Mar 21, 2002
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2,471
Sergey, thank you so much for your reply. I'm learning it's a lot more complicated than just getting the CA and PA right. I believe GIA do provide LGF and star so maybe they too can be factored into the HCA at some point.

However, based on what I'm learning here, it does seem he most important thing is to get the CA and PA right first. Following thru on my idea to have three categories of HCA recommended diamonds, I wonder if we might use your Sweetline (SW) diagram as a basis for defining those categories. With diamonds that fall along the SW called potentially Ideal, diamonds that fall on either side of the SW called Superior, and diamonds that fall into the "deeper pavilion" area called Excellent. This is what I have in mind:

MRB Cut Sweetline 2.jpg

To be honest I've no idea if I've labelled the diagram correctly, hopefully those more expert would be kind enough to comment.
Peter, Sweetline does not define grades or Optical performance . It is just a zones of similarity.

It does not give a answer which diamonds have better performance . Typical advices on PS that
1) P40.8Cr34.5 is best
2) P40.6Cr34.5 is better than P41Cr34.5

My opinion that P40.8Cr34.5 has not best performance. I prefer P41.2Cr34.5.

it is not enough to see photos to define grades, you have to compare real diamonds in real lighting conditions( outdoor, office, fire). You also have to use different backgrounds and different view working distances. Unfortunately most PS advisers never did it and just follow historical cliche.
.
 

Garry H (Cut Nut)

Super_Ideal_Rock
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14,893
Sergey, thank you so much for your reply. I'm learning it's a lot more complicated than just getting the CA and PA right. I believe GIA do provide LGF and star so maybe they too can be factored into the HCA at some point.

However, based on what I'm learning here, it does seem he most important thing is to get the CA and PA right first. Following thru on my idea to have three categories of HCA recommended diamonds, I wonder if we might use your Sweetline (SW) diagram as a basis for defining those categories. With diamonds that fall along the SW called potentially Ideal, diamonds that fall on either side of the SW called Superior, and diamonds that fall into the "deeper pavilion" area called Excellent. This is what I have in mind:

MRB Cut Sweetline 2.jpg

To be honest I've no idea if I've labelled the diagram correctly, hopefully those more expert would be kind enough to comment.
PRS as you see Sergey and I have differing opinions.
We have worked together for many years yet we have our disagreements.
We built the MSS set together as a standard for research. They will be held in perpetuity as stones for study purposes.
Sergey considers that because we have 2 eyes and based on the binary vision conflict in our minds a leakage or dark zone seen with one eye when the other eye sees a bright flash, then the mind is in conflict and creates brilliance.
You can do this when you look at a glass with a spot light source - if one eye gets a bright spot and the other does not - then that area will appear glassy shiny metallic lustrous.
Me on the other hand have seen so many diamonds with the ring of death exaggerated by oily scum on the pavilion that in my experience I prefer a slightly shallow diamond because most diamonds spend 99% of their lives being dirty.

The shallow close up darkness issue is another factor. I read yesterday that children are becoming short sighted because 1. they look at close up screens too much 2. they spend way too much time studying and 3. in order to develop proper vision they need to be outside a minimum of 2hrs a day.
This is a particular problem for Asian and Chinese kids who are more genetically likely to be short sighted - and they also are often under far more exam pressure.
So perhaps in the future I will need to do more targeted HCA based on human variables.

As for LGF and star facet ratios - 1. it is not a big issue for 90% of well cut diamonds - it is more about 'flavours' and preferences. 2. it would have required way more work than I could afford to do 20 years ago. 3. GIA did it (and breached my patent in a normal persons view) and very very few diamonds get dinged because of those factors.
 

Serg

Ideal_Rock
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Mar 21, 2002
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PRS as you see Sergey and I have differing opinions.
We have worked together for many years yet we have our disagreements.
We built the MSS set together as a standard for research. They will be held in perpetuity as stones for study purposes.
Sergey considers that because we have 2 eyes and based on the binary vision conflict in our minds a leakage or dark zone seen with one eye when the other eye sees a bright flash, then the mind is in conflict and creates brilliance.
Garry, I prefer P41.2Cr34.5 even I use only one eye.
P41.2 has stronger DETAS than P 40.8
 

sledge

Ideal_Rock
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Apr 23, 2018
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4,439
@Serg do you prefer a 34.5CA/41.2PA as defined by GIA, or as measured by your device?

What I see as frustrating is a GIA 34.5/41.2 you may see and love won't necessarily repeat the experience in a reliable way because of the variance in GIA rounding and averaging.

Whatever proportion set is determined has to account for this. The general consumer won't have the tools, software, education or patience to factor in all those aspects.

Nor will they have the luxury of seeing a boatload of diamonds and truly have the confidence to trust their eyes because their data set is severely limited and their typical purchasing viewing environment is rigged with lighting designed to make the poorest stone perform well.

We are lucky if a consumer even understands proportions at all. Most simply think GIA triple excellent are all good and equal.
 

Serg

Ideal_Rock
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Mar 21, 2002
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@Serg do you prefer a 34.5CA/41.2PA as defined by GIA, or as measured by your device?

What I see as frustrating is a GIA 34.5/41.2 you may see and love won't necessarily repeat the experience in a reliable way because of the variance in GIA rounding and averaging.

Whatever proportion set is determined has to account for this. The general consumer won't have the tools, software, education or patience to factor in all those aspects.

Nor will they have the luxury of seeing a boatload of diamonds and truly have the confidence to trust their eyes because their data set is severely limited and their typical purchasing viewing environment is rigged with lighting designed to make the poorest stone perform well.

We are lucky if a consumer even understands proportions at all. Most simply think GIA triple excellent are all good and equal.
@sledge

1) I like P41.2Cr34.5 because it creates more flashes during tilting than P40.8Cr34.5. It is easy visible in spot lights illumination ( Fire lighting).
Even newbie can see it if you ask right question. If you ask a newbie about "dead ring" he/she will see "dead ring" in P41.2Cr34.5. If you ask a newbie which a diamond have more flashes during tilting in blind tests he/she will usually select P41.2Cr34.5 .

2) Recently we have cut with high accuracy several MMD with 34,5 crown angle and different Pavilion angles. We will use them in blind tests during our optical performance workshops.

we publish only direct measurements for all angles without any rounding and averaging for all our reference diamonds .
 

OoohShiny

Ideal_Rock
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Apr 25, 2014
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7,014
2) Recently we have cut with high accuracy several MMD with 34,5 crown angle and different Pavilion angles. We will use them in blind tests during our optical performance workshops.
If they need a new home after you have finished the workshops... ;-) :D
 

GranteedEV

Rough_Rock
Joined
Nov 25, 2019
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@sledge

1) I like P41.2Cr34.5 because it creates more flashes during tilting than P40.8Cr34.5. It is easy visible in spot lights illumination ( Fire lighting).
Even newbie can see it if you ask right question. If you ask a newbie about "dead ring" he/she will see "dead ring" in P41.2Cr34.5. If you ask a newbie which a diamond have more flashes during tilting in blind tests he/she will usually select P41.2Cr34.5 .
Wpuld you say that diamond B may be less "bright" yet more "scintillating"?
 

Karl_K

Ideal_Rock
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Serg, what about color retention/enhancement in pavilion angles 41.2 and above?
color.jpg

Edit: if I recall right these are all 34.5ca
 

Serg

Ideal_Rock
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@Serg does the dead ring not bother you?

It is not visible :
1) during tilting
2) in most consumers lighting conditions( Fire, Office,..)

You need carefully align the diamond to see "dead ring" in outdoor lighting ( to see "dead ring" you need use very homogeneous light in upper hemisphere , special distance and special position)
You need special skills, special conditions or instruments to see it.

Does black reflections in main pavilion facets bother you? such black reflections are much more easy visible .
 

Serg

Ideal_Rock
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Serg, what about color retention/enhancement in pavilion angles 41.2 and above?
color.jpg

Edit: if I recall right these are all 34.5ca
I do not see a reason to discuss such RBC variations for fancy colors.
I never checked such pavilion variations in K-P colors , and I also do not see a reason to do it .

You definitely can not see the difference in table colors for RBC diamonds with I grade or better.
 

GranteedEV

Rough_Rock
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Nov 25, 2019
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5
Slightly relevant to this thread, Rhino posted a YT video comparing two rounds, one with a 34.5 deg crown and one with a 33.5 deg crown.


Probably nothing new for the regulars/trades here but as a bit of a pricescope newbie I found the side by side comparision useful.
 

headlight

Ideal_Rock
Joined
Nov 2, 2003
Messages
2,051
Forgive me if this has already been mentioned, but why are all the crown angles listed in half numbers (33.5, 34.5, etc)... no whole numbers??
Thank you.
 

gm89uk

Brilliant_Rock
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May 26, 2015
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1,443
Forgive me if this has already been mentioned, but why are all the crown angles listed in half numbers (33.5, 34.5, etc)... no whole numbers??
Thank you.
This is only for GiA which round to the nearest 0.5. so the increments are in 0.5, 33.5,34.0,34.5 etc. These are the average 8 crown angles for the diamond.

So if the average is 34.24 it'll be written as 34.0, but 34.25 will go to 34.5.
 

headlight

Ideal_Rock
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Nov 2, 2003
Messages
2,051
This is only for GiA which round to the nearest 0.5. so the increments are in 0.5, 33.5,34.0,34.5 etc. These are the average 8 crown angles for the diamond.

So if the average is 34.24 it'll be written as 34.0, but 34.25 will go to 34.5.
Thank you @gm89uk. So a GIA report with a CA of 35 can be an actual value lower OR higher than 35, based in rounding rules?
 

sledge

Ideal_Rock
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Thank you @gm89uk. So a GIA report with a CA of 35 can be an actual value lower OR higher than 35, based in rounding rules?
Not @gm89uk but yes, actual CA values can be +/- of a reported 35 value. Real values may be 34.4, 35.3, 34.8, etc. If you look at a detailed SARIN report, you will see the variance as it shows you all 8 actual values. The problem is we don't normally get the luxury of a SARIN report.

It's important to note that GIA and AGS handles this differently. AGS simply takes actual values and averages. GIA averages AND rounds, which IMO make them less reliable.

Recently there was a thread that reported a 35/40.8 (IIRC) combo on the GIA lab report. Yet the SARIN showed actual pavilion values and just averaged alone came up to 40.95. In reality, it seems it should have been reported as a 35/41. I found that particularly odd. It appears either GIA goofed or the SARIN machine needs calibrated.

The variance between actual and rounded/averaged data is what I was eluding to earlier. It's one of the reasons it's dangerous to just assume a certain set of proportions is okay. Not long ago I posted about a 34.5/40.8 combo that appeared to have safe proportions but was a train wreck in reality. Not that this combo is the golden lottery ticket winner, but many seek it because of the Tolk connection.

Either way, this article may be helpful to you. It explains how each value is rounded and also how they calculate them.

Short version:

CA = nearest 0.5 degree
PA = nearest 0.2 degree
Stars & LGF's = nearest 5%

https://www.gia.edu/diamond-cut/diamond-cut-anatomy-round-brilliant
 

Karl_K

Ideal_Rock
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Does black reflections in main pavilion facets bother you? such black reflections are much more easy visible .
I get what your saying my sister does not like h&a rounds.
She describes them as a pie with small slices removed dividing the stone up.
Where I see pretty arrows she sees a pie with bits missing.
She prefers princess cuts and my Octavia.
 

MsShnooks

Rough_Rock
Joined
Feb 11, 2020
Messages
69
I’ve just put my engagement ring diamond through the HCA and it came back at... 4.9... My earrings which came back as 1. I find it weird as I’d class the earrings as nice enough and the ring diamond looks far nicer.
 
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