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Conflicting Angle Reports

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nethead

Rough_Rock
Joined
Sep 11, 2002
Messages
9
I recently received a diamond from an internet vendor. It is a GIA certed .9, F, SI-1, 60.8% depth, 57% table. Price: $4K.

Before I took delivery I asked for a Sarin report and was advised that the crown angle was 34.7 and the pavilion angle was 40.9. This came out on the HCA at a 1.3. I was told the printer wasn't working but the numbers were put in writing on the seller's letterhead.

I took it into a lab and they ran another scan (they advised on an OGI Megascope). The readings came out with a 34.8 Crown and a 41.2 pavilion. HCA rates at 2.7.

I understand that there can be some variability in readings between machines and I have read the OGI is maybe not as reliable as Sarin. But, is this .03 degree difference something to be concerned about? Does it sound fishy?

In any event, I am happy with how the diamond looks and it is definitely an eye clean SI-1. For the money, I think I probably scored a pretty good deal even if the pavilion is actually a 41.2, so I am leaning towards keeping it.

However, I would be grateful for any opinions as to whether the seller may have "stretched" the Sarin reading to boost the HCA and if I should consider returning the stone or trying to negotiate a better price.

By the way, thanks to you experts for the great info and timely assistance. You helped steer me away from a poorly proportioned stone in an earlier post.
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
Nethead, Best Sarin and Ogi have +/- 0.1 degree accuracy when measuring pavilion angle. Some models are not as accurate and the error can be higher.

34.8 or 34.7 degrees crown angle is not a problem but light leakage increases noticeable when pavilion angle is changes from 40.9 to 41.2 degrees.

That is why you have such an increase in HCA score.
 

nethead

Rough_Rock
Joined
Sep 11, 2002
Messages
9
Thanks, Leonid. So based on a range of 0.1+- could it actually be somewhere around 40.5 and maybe within the range for the best machines? Or is a more likely explanation that one of the scans was done on lesser equipment?

I went to Gemscan in Toronto for the OGI scan. I know you are in Canada, have you heard anything about the accuracy of their machines?
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
----------------
The best way to resolve this problem is get yourself an ideal-scope.
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I'm afraid it won't be that easy, Garry. Ideal-Scope will reveal some light leakage in this stone anyway.

Without experience, Nethead will have to compare at least two stones with different pavilion angles in the same illumination conditions to find out whether this particular stone is leaking too much.
 
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