Crown and pavilion angles

[tgetz]

Hello all!

I'm new to this forum. Thanks in advance for any help, this site has already proven to be very educational.

Quick question...

Is it possible to derive crown and pavilion angles from table and depth percentages?

I'm looking at a diamond with a 54% table and 62% depth.

update- the size is 7.65 x 7.73 x 4.60




Best,


Troy

 

[Dancing Fire]

Date: 5/12/2005 6:04:16 PM
Author:tgetz

Hello all!

I''m new to this forum. Thanks in advance for any help, this site has already proven to be very educational.

Quick question...

Is it possible to derive crown and pavilion angles from table and depth percentages?

I''m looking at a diamond with a 54% table and 62% depth.

update- the size is 7.65 x 7.73 x 4.60





Best,



Troy

just ask the vendor for a sarin report.

 

[Regular Guy]

Unfortunately, agreed.

 

[tgetz]

Hi. Thanks for the replies.

I don''t believe he has this as I asked him for the angles. He only has the GIA.

 

[Spear]

I did not pay attension when they taught trigonometry in school, but I am sure this could be done using a mathematical formula.

 

[Spear]

I think that the pavilion angle can be derived using basic high school trigonometry, but only if the stone has a pointed culet.

If you had a mathematical formula that took culet size into consideration, then deriving the pavilion angle would be no problem.
But the culet size would have to be stated as a percentage of the diameter and not as terms like: thick, medium, slightly thick exc.

With all this said, I am assuming that the diamond in question is a round brilliant.

I am definitely not an expert on this subject(maths) so please don't quote me!

 

[tgetz]

Hi.

It''s pointed.

Would DiamCalc do it? I downloaded it, but it won''t allow you to do round cuts without paying $280

.

Thanks,

Troy

 

[DiamondExpert]

U can calc. the pav. angle from the pav. depth and culet % (in this case 0).

U can calc. the crown angle from the table and crown height %''s, OR from the table % and bezel facet length %.

Sorry, I know that doesn''t help much.

 

[icemyster]

What Gary said is absolutely right.....I used a basic formula incorporating the Pythagorean theorem from geometry...however...ask the cutter for a sarin because it was a totally pain in the neck to do it.

 

[Nicrez]

You will need a Sarin report to get an accurate measurement of the angles. Is it that necessary to your decision? How does the stone look? How does it fair in the other categories?

FYI: For an estimation of both angles, a trained eye could make the estimation to within a degree or two.

 

[Spear]

Date: 5/12/2005 8:47:20 PM
Author: icemyster
What Gary said is absolutely right.....I used a basic formula incorporating the Pythagorean theorem from geometry...however...ask the cutter for a sarin because it was a totally pain in the neck to do it.

tgetz,
Icemeyster is right, getting the sarin report will save you heaps trouble.


This is really an interesting topic to me!

I am busy looking at charts on the cut grades of GIA, HRD, EGL and AGS.
The problem that I have is that in the cut grade charts that I have, AGS display''s crown angle and HRD displays crown height
So how do you compare the two without converting the crown height to crown angle.
If anyone could post the mathematical formula it would be much appreciated

 

[Spear]

I think that the formula for the pavilion angle would be:

tan x = pavilion depth divided by Radius


x being the crown angle
and radius being the average diameter divided by 2

All this assuming the culet was pointed

"I literally have my old maths textbook open in front of me-lol"

 

[Garry H (Cut Nut)]

Give up.

If you have crown height etc then it came from a Sarin scan and the same report gives you crown and pav angles.

 

[DiamondExpert]

For a stone without a culet, here''s how to calc. pav. angle = Tan-1 [inverse Tan](2xpav. depth %/100).

To calc. crown angle from crown height: 100-table %, divide result by 2 and use as divisor into crown height % - take Tan-1 of result.

[These mathematical relationships are brought to you/me by Michael Cowing, p. 104 JCK June, 2004.]

 

[niceice]

Date: 5/12/2005 11:30:46 PM
Author: DiamondExpert
For a stone without a culet, here''s how to calc. pav. angle = Tan-1 [inverse Tan](2xpav. depth %/100).

To calc. crown angle from crown height: 100-table %, divide result by 2 and use as divisor into crown height % - take Tan-1 of result.

[These mathematical relationships are brought to you/me by Michael Cowing, p. 104 JCK June, 2004.]

Thanks for providing the formula Diamond Expert, it is certainly fun to play with! However for practical purposes and efficiency when sifting through parcels of diamonds, it is so much easier to just set the diamond in a Sarin or it''s equivelent and push the button... 30 seconds later, there are the results with a nifty little diagram and three dimensional model that provides the facet by facet measurements that make up the average measurements for the crown and pavilion angle measurements... A far more in-depth view of the diamond than can be obtained by traditional mathematical means of determining the measurements, especially these days when the cutters are pushing the facet structure of the diamond by stair stepping the bezel facets (kite shaped facets on the top side of the diamond) in an effort to yield more weight during the cutting process at the expense of visual performance (results in shadowed upper girdle facets)... So "Yes" as indicated you can estimate the crown and pavilion angle measurements without a Sarin by mathematical formula, but it leaves a lot of questions unanswered... Why not ask the seller to obtain a Sarin on the stone? There are an abundance of Sarin machines in the market in every major diamond market in the world, it seems impractical to us that a professional in the diamond industry in this modern age would not have access to what many of us consider to be a basic staple in our business... They start at like $5K for a basic model, for a person who is engaged in a business where the product frequently sells in excess of that amount many times over, it seems that not having such a machine in your business would be like being a carpenter without a tape measure... Sure, a lot of carpenters can eyeball the measurements when building something, but is that really the person that you would hire to build your house?

 

[Lord Summerisle]

Oh I can only wish for such a thing to become common place in GB. As it is... seems the country is still in the dark ages in terms of presenting diamond info.

The sad thing is Caroline has been looking thru some wedding mags... and even in there.. the ads for jewellers the diamonds in the pictures are so poorly cut... One was a 1/2ct ring - and the table was black!

 

[Spear]

Date: 5/12/2005 11:30:46 PM
Author: DiamondExpert
For a stone without a culet, here''s how to calc. pav. angle = Tan-1 [inverse Tan](2xpav. depth %/100).

To calc. crown angle from crown height: 100-table %, divide result by 2 and use as divisor into crown height % - take Tan-1 of result.

[These mathematical relationships are brought to you/me by Michael Cowing, p. 104 JCK June, 2004.]

Thank you for posting these two formulas!