Question for Richard Sherwood - DiamCalc Light Return Analysis

[pr0crast1nat0r]

Hi Richard,




I saw you were able to provide another newbie some simulation info on a diamond. Would you be so kind as to look at the following stone and provide me with some feedback. Thank you in advance from someone afraid to get buyer''s remorse!




Diameter = 6.46-6.49 x 4.03mm
Depth = 62.3%
Table = 55.0%
Pavillion Depth = 43.3%
Pavillion Angel = 41.4
Crown Height = 15.0%
Crown Angle = 34.7
Girdle = 1.2-1.7%
Culet = 0.5%

 

[pr0crast1nat0r]

One additional Sarin run on the same stone, by the store gemologist provided the following differences:




Pavillion Depth = 43.0%
Pavillion Angle = 40.9
Crown Height = 15.5%
Crown Angle = 34.6
Girdle = 1.0-1.7%
Culet = 1.2%




What would cause such a difference?

 

[Richard Sherwood]

Pro, those two sets of crown/pavilion angle profiles produce a big difference in the simulated light return images.

However, I don't think the 34.7/41.4 combination is correct, as it would not produce the hearts and arrows pattern which you show on the other thread. The 34.6/40.9 combination produces a H&A pattern much more similar to the image you posted, so the numbers below are for that particular profile. Nice set of numbers, Pro, especially considering that the DiamCalc program is a harsh critic.

Light Return Mono…….....Very Good 0.99
Light Return Stereo……….Very Good 0.98
(Non) Leakage Mono……...Very Good 0.95
(Non) Leakage Stereo…….Very Good to Good 0.92
Contrast………….......…....Very Good 0.95
(Non) Fisheye Effect……..Very Good 1.00

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IdealScope- In general, the darker pink areas indicate areas of greater light return, with the lighter pink areas indicating areas of lesser light return. The black areas indicate areas of greater contrast, with the gray areas indicating areas of lesser contrast. The white areas indicate areas of light leakage. A good explanation of the IdealScope image along with examples can be found at https://www.pricescope.com/idealscope_indx.asp

Disclaimer- The facet arrangement and symmetry of the image will probably vary from your actual diamond, which may affect the light performance indicated, sometimes dramatically. The image shown has perfect symmetry, which is rare, and the star facet/lower girdle facet lengths may vary from your diamond. The computer simulation is reproduced best when the actual diamond is being viewed and the image "tweaked" to the appearance of the diamond, or when the Sarin data is downloaded directly into the program. However, this "blind" reproduction should be helpful in indicating the major light performance aspects.
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[Richard Sherwood]

Just for fun I'll post the simulated image for the 34.7/41.4 angle profile. Notice the light leakage showing up inside the table as a white area, along with the much more poor contrasting effect. That is likely not the case with the stone you're looking at, judging from the H&A image you posted.

Did you buy an IdealScope so you could check it out, or does the vendor have an IdealScope image he can post for you?

 

[Garry H (Cut Nut)]

there caould be very nice hearts - but some of the arrows in the center front are missing

 

[pr0crast1nat0r]

Thank you very much for your professional replies! It is priced at the lower end of those H&A's that are on the pricescope search engine, so it looks like a decently valued stone.

 

[Garry H (Cut Nut)]

I disagree.
It is a .90-.99ct diamond that has been cut to >1.00ct.
It leaks like a seive.
It will look smaller than a well cut .90ct.

It would be a good buy at 40% cheaper.

 

[Richard Sherwood]

Garry, are we talking about the same diamond?

The first IdealScope image shown is of a 6.46-6.49 mm stone with 34.6/40.9 angle combination and mostly very good DiamCalc results.

The second IdealScope image is from a different profile of numbers which probably doesn't apply to the stone (34.7/41.4 angle combination).

The H&A image of the stone is on another thread, entitled something along the lines of H&A & Light Leakage Question. I'll bump it up so you can take another look at the image. It looks fine to me. Am I missing something?

 

[Garry H (Cut Nut)]

sorry Rich - I am stoopid

It was the 1st stone - i got confused at 6am Aussie time and answering 4 posts at the same time!!!

 

[pr0crast1nat0r]

Hi,

Cut Rock:

So would you consider the stone pictured first by Richard (40.9 / 34.6) as a worthwhile engagement stone? How about with the info shown below in the third Sarin run? It is the same stone that you replied to in the H&A Light Leakage post, that included the pictures of the H&A pattern, and which you suspected of having a cheated girdle. Do you still do?

Richard:

Amazing what a difference a few points does to the outcome. The store mentioned that lint would throw off the Sarin machine, so they steam-cleaned the stone and did another run.

Diameter = 6.46-6.49 x 4.03mm
Depth = 62.3%
Table = 54.7%
Pavillion Depth = 43.0%
Pavillion Angle = 40.9
Crown Height = 15.5%
Crown Angle = 34.7
Girdle = 1.2-1.7%
Culet = 0.4%

Again some differences. What is the maximum score on the various diam-calc categories? Is the rating between 0 and 1? Would you think that this stone could possibly have a cheated girdle? Would you consider purchasing this one knowing these figures and having seen the pictures on the other thread?

Thanks again!

 

[Garry H (Cut Nut)]

go for it

 

[Richard Sherwood]

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Again some differences.
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Yes, but a close match with the 34.6/40.9 figures, which I feel are the more correct figures. The 34.7/40.9 combo is a good looking one as well, so you should be okay in that respect.

This is an example of how photographic evidence of light return (IdealScope image) would be extremely helpful in judging the performance of the diamond. Too bad not all vendors provide that. Maybe your appraiser will have an IdealScope that he could shoot a photo from.

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What is the maximum score on the various diam-calc
categories? Is the rating between 0 and 1?
-----------

Sometimes you will see scores exceed 1.00, but usually at the expense of another parameter dropping lower. The best balancing act is scores 0.95 to 1.00 in each category, which DiamCalc calls "very good".

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Would you think that this stone could possibly have
a cheated girdle?
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Although the girdle has slightly more distance between the "peaks & valleys" (shown in your photo of the girdle) than a "super ideal", the variation is slight and just a consequence of the cutter trying to make everything work on a diamond which is on the deep side of the ideal total depth range (58.7 to 62.3% on the AGA scale). He did a masterful job of it, and I wouldn't consider the girdle as cheated.

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Would you consider purchasing this one knowing these
figures and having seen the pictures on the other
thread?
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Yes, providing the grading, pricing and optical symmetry checked out to the good.

 

[pr0crast1nat0r]

Thanks again for all the responses, you have helped tremendously in my decision. I will be whipping out that credit card soon.