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Cut Question For Experts

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Brilliant Cut

Rough_Rock
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Jun 5, 2003
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Hello..

I have a question about the height, angle, and depth variances (out of round) for a round cut stone. Is there any rule of thumb for how off they can be? The stone that I purchased is a 1A cut, but the pavillion depth varies by 1.5, and the girdle by 1.8. Just curious...For example,

Round 1.04 VS1 G
6.51 x 6.58 x 3.98 Diameter varies by .7
Total Depth 60.9%
Crown Angle 34.4 (34.1-34.9) Angle varies by .8
Crown Height 14.3% (13.7-14.9) Height varies by 1.2
Pavil Angle 40.7 (40.2-41.0) Angle varies by .8
Pavil Depth 42.9% (42.1-43.6) Depth varies by 1.5
Culet .6% Very Small
Table Size 56.6% (55.9-57.0) Table varies by 1.1
Girdle 1.4% (0.4-2.2) Medium Girdle varies by 1.8
Very Good Polish/Symmetry
No Fluorescence
 

oldminer

Ideal_Rock
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Sep 3, 2000
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You may have a diamond that has a slightly tilted table. This will make the Sarin or Megascope read as if the pavilion, and crown are both assymetric when they are not necessarily that way at all.

This is a fact known to the makers of these measuring devices, but because only a very small number of diamonds have tilted tables, tables that are not perpendicular to the plane of the girdle, nothing has been done to correct this that I am aware of.
Since the GIA does not report those details on their reports anyway, there has been little pressure on Sarin to do a more complete revision of their software.... When this issue becomes more impoortant, we may see a different software version brought to the market.
 

Garry H (Cut Nut)

Super_Ideal_Rock
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I agree with Dave.
If you can look at this diamond with an ideal-scope you can easily confirm if this is the case.
The problem is that an axis that bisects the average pavilion angle may actually have very tight proportions.
If you can post a more detailed Sarin report we can help solve the case of this particular stone.
 

Brilliant Cut

Rough_Rock
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Jun 5, 2003
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Sorry for the length of this post...

For some reason I cannot attach the report. The only other info on the Sarin provided to me is an "average graph" and a "topdown graph". The average graph has a generic picture of a round stone with the same info as I posted above. The topdown graph has no angles and only says "table 0.4% and culet 0.4%. I have seen the other sarin reports that give angles for both of these but I am assumng that that information is provided from a different model of machine. This report is from "Megascope-OGI Systems Ltd".

According to the Accredited Gem Appraisers Roung Brilliant Cut Grading Chart, the stone is a 1A for every category. Since this chart and most I have seen are based on average angles and percentages, I am assuming it would be possible to have a poorly cut stone and still have it fall into a 1A category. For instance (theoritically), a crown angle that was 31.1-37.9 on a Sarin would average out to 34.5, which is in the 1A category even though the variance is 6.8 degrees. I looked at many Sarin reports before choosing this stone and they all had average variances ranging from .3 - 2.5 and many of these fell into the 1A category and got excellent results on HCA as well as other calculators and charts I have found. This stone has been labeled a "very good" cut and not an "ideal" cut by the vendor. I am assuming the "very good" category has stones with the before mentioned variances. I have also looked at sarins from other vendors and the only stones with minimal variance are labeled H&A. So I am assuming that variance is common, but how much is acceptable?
 

Rhino

Ideal_Rock
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6,272
Actually what you are reporting is not uncommon. Quite frankly there are a lot of diamonds with "ideal" averages (as in this case an AGA1a) yet has less than ideal variances. These variances can directly affect both optical symmetry and also it's 2 dimensional symmetry. So while this diamond may have "ideal" proportions, this begs the question .. does it have "ideal" symmetry? My guess would be that it does not. And if it doesn't this is an aspect of that particular stone that would affect it's "contrast brilliance" or how brilliant the stone would appear in softer or diffuse light conditions. This is not to mention how wild the variances may be on the minor facets (as we only know the info on your majors).

Am I correct in assuming this Gary (concerning the contrast brilliance aspect)?

Peace,
Rhino
 

Brilliant Cut

Rough_Rock
Joined
Jun 5, 2003
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22
Alright, got the Sarin to attach. I went through the other sarin reports that the internet vendor sent to me prior to choosing this particular stone. Here is a summary of the individual variances of crown angle, height, pavillion angle, depth, and table for 7 different stones.

Stone(all appr. 1 ct) 1 2 3 4 5 6 7
AGS 0 AGS 0 AGS 0
Cr. ang. (degrees) 1.5 1.7 .5 1.5 .4 1.1 .7
Cr. height (%) 1.2 .7 .3 1.1 .8 .9 1.3
Pav. ang. (degrees) 1.2 .9 .7 1.3 .4 1.2 .3
Pav. depth (%) 1.0 1.2 .6 1.7 1.1 1.6 .6
Table size (%) 1.3 .7 1.3 1.6 .8 .7 .9


Stones 4, 5, and 7 are listed AGS 0 for every category. The internet vendor I dealt with did not claim any of these stones (or the one that I mentioned in the first post that I purchased) to be ideal cuts even though the numbers on 4, 5, and 7 fell as AGS 0. Would you consider these variances to be unacceptable??

I have the stone I purchased in my poessession and I think I am going to take it to a gem lab for my own piece of mind. I still can send send it back, however..........

Thanks to all...

sarin1.jpg
 

Brilliant Cut

Rough_Rock
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Jun 5, 2003
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Yeah, I figured. I ordered an ideal-scope yesterday...just to check. Any opinion on the 7 variances listed? Also, where did the "tilted table" theory come from?? What number indicated that?
 

Brilliant Cut

Rough_Rock
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Jun 5, 2003
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So the vendor who provided me with the Sarin that I posted should also have the other part of the report hat contains all of the facet angles...assuming that they saved the info?
If they have it, I wonder why they wouldn't have provided it to me for my stone?? Or the other 7 Sarins I requested???
 

Garry H (Cut Nut)

Super_Ideal_Rock
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Because BC they do not know about it, neither do 9or did GIA when they gave this near H&A's stone a 'Good' for symmetry.
Sarin know now, but seem not to care all that much.
We will publish an article about this.
It will be part of the basis for a mergered symmetry and proportion based cut grade system
 

Brilliant Cut

Rough_Rock
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Jun 5, 2003
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I see what you mean...I will try to get the info from the vendor. Ideal scope should be here next week...I think I am being too picky!
 

Garry H (Cut Nut)

Super_Ideal_Rock
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If the diamond was say P 40 with C 34.1 to P 40.8 to C 34.9 then I would not be concerned, but if 34.9 sits on top of 41, then the stone might not be as good.
As I have said before - symmetry is not a straight forward and simple thing.
This is why I have not attempted to add symmetry to HCA.
 

Brilliant Cut

Rough_Rock
Joined
Jun 5, 2003
Messages
22
I understand now....

I will first look at it under the ideal-scope, then perhaps take it to the gem lab. I think they said $125.00 for the full mapping and grading..I misplaced my notes.
 

Rhino

Ideal_Rock
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When the variances jump over 1%/' I suggest an optical analysis. But then it depends on how particular you want to get. Gary is right though ... if certain crown angles are combined with certain pavilion angles this will impact the stone negatively. It'll be interesting to hear what you observe when you look at it through an IS and compare that to their test stone which they send along with it. My educated guess is that you are going to view a very chaotic optical symmetry pattern based on those variances. And the variances you've given us do not inlude minor facet variances which will equally affect (and distort) the symmetry.

Regards & good luck,
Rhino
 

Garry H (Cut Nut)

Super_Ideal_Rock
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Yes it is a gridle cheated stone – note the main facet girdle measurements are all higher than the minor facet junction girdle measurements. So Give it a miss.
Actually the problem I originally referred too is not bad – only .6 degrees variance between Crown and also pavilion facets due to a slightly misaligned table.
Overall the girdle cheating would keep me away from it.

BTW the dealers and vendors will not have a clue what you are talking about because we have not yet had the GC article published.
 

Brilliant Cut

Rough_Rock
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Jun 5, 2003
Messages
22
I will wait for the ideal scope...........................................................................
 

Brilliant Cut

Rough_Rock
Joined
Jun 5, 2003
Messages
22
Ideal scope came.....

Internal symmetry actually looked decent, but there was a lot of white leakage on the stone. For what I paid I am sure that I can get a better cut stone. I am sending it back to the vendor shortly. Thank you to everyone for your input...

Still searching.....
 
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