GIA vs Sarin

[maximus1]

I wondered if anyone here has experienced sarin reports coming back a lot different from GIA reports.

I just bought an EC diamond where GIA says table is 66%, but then the sarin report came back with 69.6%. All the other measurements were pretty much the same on both reports.. so of course I freaked since the cut quality is a lot lower almost pushing 70 rather than just above 65. They assured me that GIA numbers are the ones to go off of, and that their machine probably needs a little recalibrating.

GIA has a good reputation, but what are the chances that GIA was off, and the seller''s report was correct? What would it cost to check again once I get it (roughly speaking)?

 

[JulieN]

GIA

you might try to measure it yourself. you probably won't end up with 66 or 70, but it should look closer to one than the other. maybe.

 

[maximus1]

forgot to mention - the seller has a great reputation, which is why I questioned whether GIA could actually be the one a little off

 

[JulieN]

James Allen?

 

[denverappraiser]

I’ll bet it’s a calibration issue, and I’ll bet that GIA is more diligent about calibrating their tools than the jeweler.

Last I checked, GIA lab uses Sarin equipment although they may have changed in the last few years. Sarin claims an accuracy of plus or minus 0.02mm on properly calibrated equipment. This leads to regular discrepancies in that 3rd decimal place with the measurements and occasionally in the second, even when the equipment is well adjusted and even when you rerun the same stone on the same machine. If there are two different machines involved this can get a little higher. If one (or both) are out of calibration it’s higher still.

Assuming that there’s no dispute over whether you have the correct stone, use the GIA numbers.

Neil Beaty
GG(GIA) ICGA(AGS) NAJA
Professional Appraisals in Denver

 

[neatfreak]

Not calibrating your machines can really really make a difference in accuracy.

This isn't a great example, but it works, so here goes: Cops are required to calibrate their radar guns everyday. If by chance you should get pulled over and cited for speeding, when you go to court you should ALWAYS ask if the cop calibrated the radar gun that day. If the answer is no (which it often is despite the rules) then you will almost always get off because the judge then can't actually determine whether the gun was accurate or not and thus whether you were really speeding or not.

So bad example aside, the point is that if your appraiser by chance didn't calibrate their instruments (which is more likely than GIA not calibrating) they could be off a bit. So I also would trust GIA more.

 

[RockDoc]

Some of the variance might be related to the size of the stone.

A 3% variance on a stone measuring 4 mm in width is a pretty small measurement in actual size difference. A 3% table size difference on a large stone, is more of an issue than a 3% difference in a smaller stone. In that the 3% is a calculated result, compare the width measurement from the two reports too.

Additionally, a tiny piece of dust, could skew the table measurement as well.

In some Sarin models, there are changeable lenses which are for varying size limits of the diamond measured. The ones at GIA probably have changeable lenses. Appraisers, usually have the fixed lens model as it is about half the price of the changeable lens model.

Many retails jeweler have an older model called the Brilliant Eye, which is not as accurate as the "larger" models. This one was a lot less expensive than the Diascan model or the Diamension models, and less accurate.

In that the table appears to be the only measurement that varies from GIA to your appraiser''s machine, it is difficult to know which machine was/ is more accurate.

Hope this helps

Rockdoc