GCAL analysis and their photomicrographs?

[Mikesgirl]

I''ve been considering a round brilliant diamond with Blue Nile that is in their signature collection. It is HCA .7, AGA 1A, AGS graded Ideal for Cut, G, VS2, .701 cts. It measures table 57%, depth 60.6, 14.6% crown (34.2 degrees) and 42.7%pavilion (40.6 degrees). Two things: The AGS report states the girdle as .9 to 1.4%, whereas the GCAL reports it at 3% (quite a difference) - which should I trust more, or is it a matter of equipment? Second, what is the photomicrograph supposed to tell me? It reminds me of the H&A analyses I''ve seen, but Blue Nile makes no H&A claims. It shows very definite balance, but the arrows appear dark and the hearts light. I can find nothing on the internet about photomicrographs as they apply to diamonds. Info, anyone?

 

[Richard Sherwood]

Hi Martha. The AGS girdle measurement you mention is taken from the "valleys" of the girdle, while the GCAL measurement is probably taken from the "peaks" of the girdle.

I'm not sure about the photomicrograph. Do you have the URL address for it?

 

[Mikesgirl]

Thanks for the feedback. I noticed the Sarin reports at GOG also show a single higher percentage, so I guess it's not unusual. I'm a lefty and want to be sure I'm not getting a stone with too thin a girdle to wear it safely.

The URL is

http://www.bluenile.com/diamonds_details.asp?pid=LD00681105&item=60_86&filter_id=0&sec=&query=20&page=4&sortby=size-d

This will take you to a page that you can click on the "see GCAL report" button and zoom in to see the photomicrograph of the stone at the bottom. This is not the stone I am considering, as I requested it to ship for exam so it can no longer be viewed on line. The photomicrograph for the stone I've requested is very symmetrical and balanced.

Thanks again -

 

[Richard Sherwood]

I took a look on the URL you gave me. The GCAL lab is Donald Palmieri's New York lab. Donald Palmieri is a well known and respected appraiser.

The photomicrograph appears to be a "dead on" photo, magnified. It doesn't appear to be a proportional image like an Idealscope or Hearts & Arrow image, but the optical symmetry of a stone will definitely be observable in such a photo.

The stone you are looking at has a great set of proportions. I ran it through the DiamCalc software and came up with the following POSSIBLE Light Return Analysis, along with the following POSSIBLE simulated IdealScope image. The numbers are top drawer, along with an excellent image.

Light Return Mono…….....Very Good 0.98
Light Return Stereo……….Very Good 0.96
(Non) Leakage Mono……...Very Good 0.96
(Non) Leakage Stereo…….Very Good 1.00
Contrast………….......…....Very Good 0.95
(Non) Fisheye Effect……..Very Good 1.00

-----------
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.
-----------

 

[Mikesgirl]

Wow - above and beyond the call. Thanks for the feedback. I am replacing my 11 year old engagement ring recently lost, and it was a beauty. I am worried that I won't be happy with the "sparkle" of a replacement but don't know if the premium I would pay for hearts and arrows, etc, would be justified. The only remaining concern is its only flaw - a star shaped "cloud" (according to the GSA report) that occupies a space below the table about 1/6th of it's area. But being that it's VS2, I think it's worth the risk of having to return it to find out how it looks. They're asking $3255 for the stone. I guess I'll spring the $25 for the ideal-scope so I can look at it more clearly when it arrives.

Thanks again, so very much, for the help. If only you were in the Washington Metropolitan area so I could bring it to you for appraisal. Isn't the net wonderful!

 

[Richard Sherwood]

In the Washington Metropolitan area you've got Martin Fuller and Pennye Jones-Napier who both have good reputations as appraisers.

I wouldn't worry too much about the cloud. If it got a VS2 from the AGS it must be highly diffuse and transparent, unable to be seen with the eye.

The price sounds very fair.

Congratulations!

 

[Rhino]

What probably concerns me most is the deviations between the crown and pavilion angles regarding the AGS Report and and GCAL report. AGS report says 34.9 with 41.1 pavilion angles. That will perform quite differently than a diamond with 34.7/40.8 angles. HCA scores are quite different too. My Sarin and OGI's are usually dead on or +/_ .2 within the AGS #'s so it may be worth it to have it checked with an appraiser. Rich... show her the graphic using the AGS #'s.

Peace,
Rhino

 

[Richard Sherwood]

Those two sets of proportions are not for the stone she's considering Rhino (AGS-34.2/40.6), but the difference between the two profiles you mention is interesting. I didn't catch that. It makes for a big difference in predicted light return.

34.9 / 41.1 angles (AGS)
vs
34.7 / 40.8 angles (GCAL)

Simulated images for these two profiles follow (again this is not the stone you're considering Marty).

I wonder whose machine is off?

 

[Richard Sherwood]

34.9 / 41.1 angles (AGS)

 

[Richard Sherwood]

34.7 / 40.8 angles (GCAL)

 

[Richard Sherwood]

Which proves Rhino's point about having it checked out by an appraiser.

When viewed firsthand under an IdealScope for example, an appraiser could confirm if the stone had light leakage such as that portrayed by the AGS configured image above, or a superior light performance such as that portrayed by the GCAL configured image.

Nothing beats firsthand observation. You might want to check out (and let us know) the variance between the two sets of reported angles on the stone you're looking at, Marty, and go ahead and purchase an IdealScope so you can verify things with your own eyes.

 

[Mikesgirl]

I printed all of the info out before ordering the stone. The GCAL measurements are: Table, 57.6; Depth 60.3; Crown 14.3% (34.0 degrees); Pavilion 42.4% (40.4%); 3% girdle; 1% culet. It came up .7 on both sets of stats for the HCA, 1A with GCAL on AGA and 1B with AGS on AGA. I can't thank you enough for running these numbers for me. And I'll check with those appraisers - I guess they are equally qualified, just a matter of convenience/distance for me?

 

[Richard Sherwood]

Okay, so those two sets of numbers are much closer in variance than the previous two sets (AGS-34.2/40.6 vs GCAL 34.0/40.4). Both of those angle combinations predict a well performing stone, so you should be in good shape.

I don't know which of the two appraisers is more competent in the area of ideal make stones, so you might ask a few questions to determine if they feel comfortable in that area. A lot of appraisers are not specialists regarding the ideal and super-ideal makes.

You always have the option of having the stone mailed to a non-local appraiser by the vendor for a professional analysis before having it forwarded on to you for a visual inspection.

 

[Mikesgirl]

I'll let you know how it turns out. Again, much gratitude.

 

[Mikesgirl]

Here's the stone I was inquiring about, from Blue Nile. I'm very pleased with it - it has beautiful color and sparkle in all kinds of light. I want to thank you for your feedback, Richard and Rhino. It helped to reinforce all I'd learned in this purchasing process. This stone is certainly as beautiful as my original, if not more so. I'll post more pictures on the "Show me" board. Thanks again!

 

[Richard Sherwood]

Very nice, very nice.

Congratulations!