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# Crown and Pavilion Angles

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#### abilu

##### Rough_Rock
GIA doesn''t give the crown and pavilion angles. Can I calculate these angles or percentages using the l x w x d and depth / table? I tried some trig. but it gave me funny results.

#### pqcollectibles

##### Ideal_Rock
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On 6/6/2003 12:42:16 AM abilu wrote:

GIA doesn't give the crown and pavilion angles. Can I calculate these angles or percentages using the l x w x d and depth / table? I tried some trig. but it gave me funny results.
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Hi Abilu!

Unfortunately, no, you cannot calculate the angles. Someone posted formulas to try that, but they didn't work. You get much the same result as if you just use Crown and Pavillion %'s. This may be a function of the girdle thickness???
I really dunno for sure.

My personal experience has been that using the %'s gives you a "ballpark" of half the actual score. If using %'s yields a score of .6, then the true score will be somewhere in the "neighborhood" of 1.2, with key being in the "neighborhood".

You could try contacting the vendor for Sarin info on the diamond. Maybe they will supply you with the numbers you need to use the HCA.

#### phantom

##### Rough_Rock
Well if GIA doesnt' give Crown and Pavillion than what is the best way to find out if it is good cut? Get the sarin report?

#### jlim

##### Shiny_Rock
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On 6/6/2003 1:27:57 PM pqcollectibles wrote:

Unfortunately, no, you cannot calculate the angles. Someone posted formulas to try that, but they didn't work. You get much the same result as if you just use Crown and Pavillion %'s. This may be a function of the girdle thickness???
I really dunno for sure.
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PQ, if someone can calculate the angles simply based on the table and depth percentage together with the "length" and "width" of the diamond as well as the depth of the diamond, this person would re-write the history of mathematics.

In a triangle, if you only know 1 dimension and no knowledge of an angle, it is impossible.

#### pqcollectibles

##### Ideal_Rock
Yeah, Phantom, you have to ask for Sarin info in GIA Certed diamonds. One of the experts here posted that GIA runs Sarin on every diamond they Cert. Only the "owner" of the diamond that submitted it for grading can get the Sarin report from GIA. That could be a broker or 2 removed from a "Drop-Ship" or B&M vendor and hard to get.

Jlim~
Someone posted some formulas to calculate angles. I posted them in several threads without trying them out first. Then one of the experts pointed out that they didn't really work. So, I tried them using the info from my AGS diamond Cert, and they didn't work. The results were very similar to what you get using %'s. My diamond rates a 1.4, if I remember correctly. I got .6 using %'s and .7 using the formulas.

Would be wonderful if someone could come up with formulas! I feel confident that the girdle thickness must be a part of the error. One of the vendor's websites shows a method to approximate the angles, but you have to physically have the diamond in hand to do it.

#### Mara

##### Super_Ideal_Rock
I think in the past Leonid has posted calcs that will help you somewhat accurately convert %'s from something like an EGL cert to angles for the HCA. But to have nothing and find out the angles? Not gonna happen!

#### jlim

##### Shiny_Rock
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On 6/6/2003 4:29:30 PM pqcollectibles wrote:
Would be wonderful if someone could come up with formulas! I feel confident that the girdle thickness must be a part of the error. One of the vendor's websites shows a method to approximate the angles, but you have to physically have the diamond in hand to do it.

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pq - I haven't really thought about finding the % instead. Maybe that's doable. I just know you cannot get the angles. Actually, you cannot get the % either from the info you get from a GIA cert. But if you have the %, you could theoretically get the angles. But like the old sayind, "garbage in, garbage out". So, if the % aren't accurate, the angles will be way off.

I would hate to have to pull out my old protractor to measure angles on a 3D object with a .5 graduation.

But you could theoretically take a photo of the diamond using a high MP camera and dump it into any engineering software. Then it is easy to measure the angles. That should work better.

#### pqcollectibles

##### Ideal_Rock
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On 6/7/2003 2:12:38 AM Mara wrote:

I think in the past Leonid has posted calcs that will help you somewhat accurately convert %'s from something like an EGL cert to angles for the HCA. But to have nothing and find out the angles? Not gonna happen!

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Those were the formulas I was talking about, Mara. They don't work. I plugged the %'s from diamond in the HCA and got nearly the same result as I got figuring angles from %'s with Leonid's formulas. That HCA score using %'s or calculated angles was about half the true score obtained using the real angles from the Cert.

Jlim~ That was exactly the example shown in the pic. Lay something flat across the table of the diamond and approximate the angle. LOLOL Your idea sounds much easier, using a computer model. You should work up a program and patent it. I'd bet you'd make a fortune!

I just checked out Gary's link. It has the Tolkowsky Ideal cut. Table is 53% and all the angles are set numbers. But then again, Tolkowsky's model had a knife edged girdle too. So I guess what we've been seeing graded as Ideal cuts aren't, for the most part, "True Tolkowsky Ideal" cuts. But they come very close and are some of the most beautiful diamonds available.

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