GIA & Sarin...who''s more accurate?

[biscuit]

Hello All!

I had some specs sent to me by an online vendor, and included with the email was a scan of the GIA dossier and a printout from a local sarin of sorts. They differ in two places from what I can tell...

The GIA report states that the table % is 57%.
The Sarin states that it is 55.3%.

The GIA report states that there is no culet.
The sarin states that the culet is 1.3%.

This info comes from a vendor that is given very high ratings on pricescope, so I'm trying to figure out if my understanding of these reports is wrong or if the vendor made an error.

Of these two reports, which is the most accurate? Could both of these reports be accurately representing the same diamond (through some sort of averaging...granted, pretty funky averaging)? I'm guessing that the most accurate would be the GIA, and BTW it is laser inscribed with the GIA # so I could, at the very least, match the rock with the GIA cert...

Any help would be appreciated!

Thanks a ton, all!

 

[biscuit]

Sorry!

I posted this question without searching the forum...after doing that I found that this question's been addressed a few times over the last year.

I wasn't able to find any difinitive answer on which report is more accurate...GIA or an individual gemmologist's sarin machine? Also, given that there is some acceptable variation in AGS/GIA/Sarin reports, are the numbers I mentioned above acceptable variations?

Thanks a ton!

 

[oldminer]

No variation is truly acceptable. All the major labs use Sarin machines. We use Sarin and Ogi machines. None of them give totally identical results except by accident. We hand measure, with electronic tools, to verify the results as credible on most lab reports when we are verifying if a stone matches a given report from another lab.

Expect differing results. Thankfully, this is not rocket science or we would miss landing on the moon.

 

[mdx]

Hi Biscuit
We have found that manual measurement is certainly more accurate that Sarin but too time consuming. If you have large volume to Asses then Sarin is the practical way. As Dave says its no rocket science

 

[Garry H (Cut Nut)]

I suspect there is a mix up of stones with as much as 1.7% error.

 

[biscuit]

Hi All!

Garry - to be honest, if you're right, that's a little disturbing. I'm not sure whether to think this was an honest mistake or whether the cutter/wholesaler "produced" a fake sarin to make this rock look good (all of the conditions/angles are almost Tolkowski ideal dead on). I hate being a genXer...too darn skeptical!

One would think that an error of this nature would have been caught passing through so many hands before getting to the consumer (the rock's currently at a third party's lab)...and if caught, then explained with the certificate's delivery...one would think that most consumers that actually know enough to ask for crown/pav angles would notice, right?

When I brought it to the vendor's attention, they explained it as being due to variance in machines, and that ultimately the GIA cert was the accurate one. Funny, the rock is represented on their website and in emails as a 55% table. But after the conversation, they started calling it the rock with the 57% table.*

*note to vendors: this doesn't actually help to establish trust.

Thanks for your thoughts, all!

 

[Garry H (Cut Nut)]

Does the 3rd party appraiser have a proportion analyser?? - it will be interesting to follow this up Biscuit.

But honest mistakes can and do happen. And 55% or 57% is hardly a difference in quality.

 

[oldminer]

The jewelry trade follows the GIA-GTL results as if it was free of all errors. Even the GIA-GTL has a certain degree of latitude in what passes as "accurate enough". The faith the trade and the public put in GIA is most commendable, but no lab gives perfect results every time. Human error and machine error exist, and for the time being, live with it and hope for ever increasing accuracy. Because of continuing research in many places there will be better and more consistent grading, higher accuracy and improved re-identification procedures in coming years.

Since a machine can't talk back or join in an argument, we are forced to accept machine derived results. While Sarin and Ogi results are very good, they can vary from machine to machine. "Close enough" is generally accepted as "accurate" and in mass grading the labs just don't re-check every last measurement. A percent here and there, a degree here and there, a tenth of a mm, all get by from time to time. Don't worry about it. Just do what you can to be sure the stone is the one that was graded for the report it is accompanied by.

 

[fubini]

Sorry to butt in, but I have a similar question that doesn't seem to have come up before--what if you get an OGI report whose percentages on the average graph match exactly the GIA report, EXCEPT that the actual measurements for a couple of the characteristics (in mm) are way off?

The errors occurred on the same characteristics (table and girdle) on reports for two different stones from the same vendor, so I'm inclined to believe that maybe their machine is really malfunctioning. But, I still find it weird that the measurements didn't match the percentage (of diameter) numbers.

If the machine were malfunctioning, wouldn't both the measurements AND corresponding percentage numbers be miscalculated?

Thanks.

 

[Garry H (Cut Nut)]

Not neccisarily.
i do not know about Ogi, but Sarin measures angles and a 'construction' of join the dots is used to 'measure' the stone and calculate the %'s.
That is the minor one of the reasons why we insist you use angles not %'s in HCA