Acceptable crown / pavillion angle deviation?

[jenniann]

Hello!

I''ve a quick question that I''m struggling to find an answer to and hope I can pick the brains of you cut perfectionists out there - what is an acceptable level of deviation on the crown and pavillion angles in a H&A AGS000 (it is a WF ACA by the way)?

The diamond I''m looking at has a variation of 0.6 degrees in both the crown and the pavillion. the crown ranges from 34.7 - 35.3 (average 34.9 on the Sarin, 34.8 on the AGS cert) and the pavillion form 40.4 - 41(average 40.7 on the sarin, 40.6 AGS cert). Is this anything to be concerned about or is this quite acceptable?

The other stats for reference are:
0.80ct
Depth 61.2
Table 56.9
Crown% 15.1%
Pavillion 42.8%
HCA 0.8

Thought and opinions greatly appreciated!

Thanks in advance

 

[stone-cold11]

It is acceptable. If not, AGS will not give it an ideal symmetry grade and the cut grade will be dinged to maybe an AGS1.

 

[Lorelei]

AGS measurements are always considered the authority according to the experts here so those are the ones to go with, various things can affect the results of a Sarin, the skill of the operator, calibration etc and some variance is usual.

 

[Garry H (Cut Nut)]

Sounds like a diamond with a slightly tilted tabel (by 0.3 degrees) and this causes virtually no disturbance to the light rays entering and leaving the diamond.
http://www.gemology.ru/cut/english/symmetry/6.htm this is an article about tilted tables

 

[jenniann]

Thanks for those comments, looks like nothing to worry about then. I didn''t seriously think there would be, I know Brian has left WF now but judging by the date on the cert this one pre-dates his departure and I can''t imagine he would have let it through if there was an issue.

Garry, thank you that link, can I just ask on question off the back of that article? Does the AGS symmetry system take account of a tilted table or has the diamond recieved a 0 grade for symmetry even with the 0.6 deviation (assuming for a moment that that''s correct and not a reading error in the Sarin)?

Just for info here are the IS and hearts images:

 

[jenniann]

Hearts

 

[strmrdr]

I totally ignore anything the WF sarin says and just look at the reports numbers. (other than CH for step cuts)
They calibrated it and had it serviced but still didn't seem to get as good results with it as some do.
Others sarin machines get measurements much more inline with AGS report numbers.
With the numbers on the reports and the images available it isn't really needed anymore anyway.
It takes a helium scanner to really play the tightness game anyway.

 

[Lorelei]

the images looks great Jenn.

 

[jenniann]

Thanks strmrdr, that''s also good to know, I''ll focus on the AGS report and the pictures.

Lorelei -

I can''t wait!

 

[Lorelei]

Date: 2/16/2009 4:30:34 AM
Author: jenniann
Thanks strmrdr, that''s also good to know, I''ll focus on the AGS report and the pictures.

Lorelei -

I can''t wait!

I''ll bet!!!

 

[John P]

First of all nothing wrong with this diamond. The images tell the story - beautiful.

Date: 2/15/2009 2:24:51 PM
Author: Stone-cold11

It is acceptable. If not, AGS will not give it an ideal symmetry grade and the cut grade will be dinged to maybe an AGS1.

As a point of order this is not quite right SC. The lab symmetry grade evaluates only facet symmetry (shape, meet points) and proportion symmetry (table-culet off-center, wavy girdle etc). There are a number of elements it fails to consider - 3D optical symmetry and tilted table among them.

While PA and CA variance is perfunctorily addressesed in proportion symmetry downgrades occur only in extreme cases. There are situations where variance can create leakage zones that go unaccounted-for in the symmetry grade - and in GIA's case the cut grade. See this post for such an example (GIA EX EX EX).

I'll reiterate again that the diamond in question is perfectly wonderful.

 

[jenniann]

Thanks John, I can''t take any credit for the appearance of the diamond but I''m very glad you approve!

I ended up with one of the aforementioned GIA ex/ex/ex first time round so am determined to get it spot on this time (actually, My GIA isn''t as bad as the one cited and will be off for a new life with a partner as studs but I want something rather more spectacular for my finger).

Based on your comments John, am I correct in thinking that excessive variance in the angles would show up in the IS as leakage or mis-shapen hearts / arrows rather than affecting the visual performance of the diamond (in terms of brilliance, contrast etc)? For future purchases (

) can I basically ignore any variance reported in the Sarin if the IS looks good and the diamond is scoring 0''s?

Am also correct in thinking that a tilted table (if that is what it is) is perfectly fine so long as the factors above hold true?

Questions, questions.........how simple life was before PS (man I fell like a nerd!)

 

[John P]

Welcome to the insanity Jennian.

Date: 2/16/2009 2:35:27 PM
Author: jenniann

Based on your comments John, am I correct in thinking that excessive variance in the angles would show up in the IS as leakage or mis-shapen hearts / arrows rather than affecting the visual performance of the diamond (in terms of brilliance, contrast etc)? For future purchases (

) can I basically ignore any variance reported in the Sarin if the IS looks good and the diamond is scoring 0's?

My policy is not to ignore any data. Rather, I try to work from a preponderance of information. With that said, scans are improving but remain far distant to actual images with regard to the weight I place on them.

Just to "nerd out" a bit more, consider this: If the PA has a variance of 40.6-41.0 the net result optically may be precisely 40.8 if those two mains (the one that's 40.6 and the one that's 41.0) are opposite each other. Alternately it could indicate a potential leakage zone. And that is just the 8 pavilion mains; we haven't touched-on the fact that variance in the 16 lower halves is not represented. These facets account for even more bottom surface-area than the mains. This means it's possible to see PA 40.8 (40.8-40. but have poor cut precision 'round most of the bottom half. Nothing on a report will reveal that.

In the case of this diamond the Ideal-Scope and hearts views clearly show the opposites average for a proper net-result (this may have been strategic on the part of the cutter), or there is a slightly tilted table as Garry alluded to. Either way the variance is a non-factor in this case, as shown in the reflector images.

Hopefully the above helps to explain why many cut-focused experts will not comment decisively about a diamond when only the numbers are reported. Let's have proper images.

 

[Lorelei]

Great posts Sir and very informative!

 

[jenniann]

Thanks John! Sorry, I completely missed your last post.

Yes, I completely see why it isn''t possible to give a definative answer by the numbers alone, I''m slowly building up my understanding of these things - it wasn''t that long ago I thought all I needed was table and depth %

Thanks again to everyone for your input - see you on SMTR in a couple of weeks!