Question about diamond diameter

[bling]

hello,
i have a question about diamond diameter. on my cert, the mm is 6.86x6.89. Today, when i took it to the jeweler, they whipped out their calipers and measured the stone..it read like 6.57 to 6.67 to 6.71..but nothing close to what it says on my cert or my appraisal? How can this be? they weight was exactly the same however? can instruments be off? and please dont tell me this is method of scamming because they have my stone as we speak! thanks

 

[oldminer]

Assuming everyone is being honest, there are many different degrees of accuracy in measuring tools that jewelers and appraisers use. Even Sarin and Ogi devices need periodic calibration. Most of the time a difference in measurments is the result of less than perfectly calibrated tools and very little standardization.

It is sufficient to question what is going on, but I suggest closwer questioning of the tools the jeweler used. If it is a dial Leveridge gauge, it is not accurate to 2 decimal places. It would need to be a digital caliper or dial gauge to be more accurate. Even then, it may not measure perfectly.

So, don't be overly upset, but do check out the equipment. Sometimes we find major lab equipment is not perfectly calibrated, too.

 

[valeria101]

well.. the dianond stays the same, I would guess. And the variation of numbers is well within measurement error, sure so.

This thread would make great reading for whoever still wants to hunt down the that tenth of a milimeter and claim it shows

 

[bling]

not to beat a dead horse..but it was off by like 0.3 ish mm. my stone is 1.2 and measured on the cert 6.86 and nothing they measured in the store even came close? the calipers they were using had a digital read out, but thats all i could tell.
please tell me i have nothing to worry about..

- the overly paranoid! thanks

 

[WinkHPD]

Were they measuring the stone while mounted? If so it is very possible that they were not getting the calipers exactly oposite one another at the greatest diameter. It does not take much of an error looking by the eye to miss measure by .3mm.

Normally we would lay the stone table down and close the wide part of the calipers on the stone while parallel to the stone so that getting the correect placement is automatic. Often when measuring a mounted stone the mounting interfers with that so we try to measure while holding the calipers perpendicular to the stone, thus introducing much greater probability of errors.

Wink

 

[Superidealist]

What is the carat weight of your diamond? Assuming it is well cut, it is possible to very accurately estimate the diameter from the carat weight and vice-versa. The diameters you mention correspond to significantly different carat weights (assuming a well cut stone). These values are shown below.

6.57mm : 1.03ct
6.67mm : 1.08ct
6.71mm : 1.10ct
6.875mm : 1.18ct (6.875mm is the average of the two numbers listed on your cert)

This may help you judge which reading is most accurate.

 

[Garry H (Cut Nut)]

It is really easy to measure a stone in a circular guage style leveridge and read it upside down and write the wrong # down.


Either the lab or the jeweler could have done this inadvertently.


As SI says - give us all the dimensions and wt and we will tell you which is accurate

 

[bling]

thank everyone for the help. its an ideal cut stone and its 1.20ct. the measurements from the cert and appraisal are 6.86x6.89x4.21mm. so it seems to be on according to SI's posting. i think they were just quickly doing the measurement..just to add it to the description before they did the work on my ring. id like to think...all is well.
however, when i received my ring back..about 2 hours later..i looked for the lazer inscription and the black had been "cleaned" off. I had asked them to be sure to remove any black dust fromt he girdle, since its not faceted..and in doing so, they cleaned the black from the inscription as well. i had a hard time seeing it, but they took me to the back and let me look at it through their microscope..so its there, i just cant see it like i used to. any thoughts on this? thanks again all!