GIA Cert - Crown & Pavillion

[diane1]

Hi,
Can anyone tell me if there's a formula to figure out the crown and pavillion percentages with the measurements and info on the GIA cert? Thanks

 

[pricescope]

unfortunately no

sometimes if diamond is not deep it is possible to tell whether it has good proportions only based on table and total depth though

 

[scotch]

Leonid,
if there is no such formula, how come the DiamCalc program is able to calculate (or rather, approximate) the angles from the GIA dimensions? ..just asking.

Scotch

 

[pricescope]

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On 11/15/2002 4:32:34 PM

Leonid,
if there is no such formula, how come the DiamCalc program is able to calculate (or rather, approximate) the angles from the GIA dimensions? ..just asking.

Scotch
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One can play with crown and pavilion angles knowing carat weight, depth, table, measurements, girdle, and culet using DiamCalc. However, there might be more than one solution.

For instance, a report says 'thin to sl.thick' girdle. But this is just min and max. You don't know what the average thickness is.

Or measurements 6.50-6.56 mm. Again it is just min and max diameters. We don't know the average diameter or whether it is slightly oval or square.

Hope this make sense.

 

[diane1]

If that's true re DiamCalc, does anyone out there have the software and could plug in dimensions for me (the free version does not allow for round brilliants). The measurements are 6.33 - 6.39 x 4.02. Table is 57 and depth is 63.2. P/S VG,VG Color G, SI1. Girdle Thin to Thick, F (the worst inclusion is a natural one on the girdle/crown - could that be why it got the thick, cuz it doesn't appear thick anywhere else?)
Thanks

 

[diane1]

It may not be a perfect method, but please give it a shot. FYI the culet is none.

 

[pricescope]

without DiamCalc I can tell the diamond is not ideal cut - a bit deep for the table size.

 

[diane1]

But couldn't it still rank high on HCA? It is much more beautiful in the qualities HCA judges than another one I looked up that got a 1.3 on HCA.

 

[pricescope]

sorry but HCA for this stone > 2 for any reasonable combinations of crown and pavilion angles.

If you want HCA < 2, keep looking. What is the carat size of this stone by the way?

 

[diane1]

1.01. I will call the jeweler and see if he has -- I'm very curious now.

 

[pricescope]

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But couldn't it still rank high on HCA? It is much more beautiful in the qualities HCA judges than another one I looked up that got a 1.3 on HCA.
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Could you tell how and where did you look at the diamond?

Deep cut stone can look nice unset because they allow the light to go through pavilion. Once set they die.

 

[pricescope]

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1.01. I will call the jeweler and see if he has -- I'm very curious now.
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Here is a food for your thoughts. Well cut 1.01 carat diamond should have 6.52 mm in diameter. This stone is deep and has smaller diameter.

6.36 mm is a diameter of well cut 0.93 carat diamond. It will be cheaper and look better.

Diane1, please don't get me wrong, I'm not talking against this diamond. If you like it you should go for it. You might want to check it with independent appraiser to be certain.

 

[diane1]

Thanks. I noticed the table was deep and the spread smaller than the other 1.01's with good dimensions, but it had more fire and brilliance and the inclusions weren't visible to my naked eye. Is it possible that it could have more fire and brilliance than others that make the grade? I really do have a good eye.

 

[diane1]

I saw it both set and unset cuz we bought the damn thing. It's more beautiful in the setting, which is simple 6 prong with platinum band. Am I nuts -- maybe I'm tilted perpendicular to the universe. What detracing factors should I notice w/ too much depth, not enough diameter?

 

[diane1]

Ok -- I got the crown & pavillion angles: 34.9 and 40.9, respectively. I ran the HCA and got a 1.7, Ex, Ex, VG and spread an obvious G. Is this impossible? I can always upgrade with full credit, but this one showed better than others that are more ideally cut. I promise after you respond to this I won't monopolize your time!

 

[pricescope]

Diane1, very intriguing!

Diamond with 34.9 deg and 40.9 deg crown and pavilion angles should be pretty nice. However, it cannot have 63.2% total depth and if it is 1.01 carat it should be 6.50 mm in diameter.

I attached a snapshot from DiamCalc for 1.01 carat with 57% table, 34.9 deg and 40.9 deg crown and pavilion angles.

As you can see its total depth = 3.97 mm, i.e. 61.1%.

How crown and pavilion angles have been measured?

 

[diane1]

So, is it mathematically impossible?? The jeweler has a Sarin machine that he said he used. He is totally willing and eager to upgrade, so it is utterly implausible?? Like I said, it has much fire and brilliance versus more traditionally ideal cuts. Thanks much.

 

[pricescope]

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So, is it mathematically impossible??
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Yes. It is impossible to have 34.9 and 40.9 crown and pavilion and 57% table and 63.2% total depth.