Calculating the Crown Angle

[chonc76]

Hi All,

I wanted to ask a very technical question that only the most qualified can answer definitively. I deciding whether or not to buy a round brilliant stone that was GIA certified in 2000 and unfortunately they didn't measure the Pavilion Angle only the Crown Angle; nor did they assign a cut grade during that time. The specs of the stone are below:

Round Brilliant
Measurements: 6.27 - 6.32 x 3.79 mm
Carat Weight: 0.91 carat
Color Grade: F
Clarity Grade: VS2

Proportions:
Depth: 60.2%
Table: 60%
Crown Angle: 33.0
Pavilion Angle: ??
Girdle: Thin to Medium, Faceted
Culet: None

Finish:
Polish: Good
Symmetry: Good
Fluorescence: None

Can the other missing dimensions/angles be calculated based on the above information? I'm trying to determine the cut grade based on the dimensions of the stone. I saw an article here about the myth of 60/60 which this diamond falls into so I wanted it to ask some experts if this could be a very good to excellent cut stone.

Second question, given all the information what is a fair price for the stone?

I hope I didn’t overstep the boundaries of this forum and I appreciate any advice technical experts can give.

 

[Deia]

Posted this here for you as maybe you'll get more answers there! I messed up on the e though lol, sry!

[URL='https://www.pricescope.com/community/threads/calculating-the-pavilion-angle.165453/']https://www.pricescope.com/community/threads/calculating-the-pavilion-angle.165453/[/URL]

 

[prettyshrewdsellers]

Posted this here for you as maybe you'll get more answers there! I messed up on the e though lol, sry!

[URL='https://www.pricescope.com/forum']https://www.pricescope.com/forum[/URL]

Hi All,

I wanted to ask a very technical question that only the most qualified can answer definitively. I deciding whether or not to buy a round brilliant stone that was GIA certified in 2000 and unfortunately they didn't measure the Pavilion Angle only the Crown Angle; nor did they assign a cut grade during that time. The specs of the stone are below:

Round Brilliant
Measurements: 6.27 - 6.32 x 3.79 mm
Carat Weight: 0.91 carat
Color Grade: F
Clarity Grade: VS2

Proportions:
Depth: 60.2%
Table: 60%
Crown Angle: 33.0
Pavilion Angle: ??
Girdle: Thin to Medium, Faceted
Culet: None

Finish:
Polish: Good
Symmetry: Good
Fluorescence: None

Can the other missing dimensions/angles be calculated based on the above information? I'm trying to determine the cut grade based on the dimensions of the stone. I saw an article here about the myth of 60/60 which this diamond falls into so I wanted it to ask some experts if this could be a very good to excellent cut stone.

Second question, given all the information what is a fair price for the stone?

I hope I didn’t overstep the boundaries of this forum and I appreciate any advice technical experts can give.

rockytalky/calculating-the-pavilion-angle-t165453.html

Not enough info to calculate PA as we would need actual max and min girdle thickness in %.
Good Polish and Symmetry unless the criteria for those was different is not a good sign either.

 

[denverappraiser]

GIA didn't calculate a cut grade before 2006.

You may be able to get more information, including the pavilion angle, over the phone if you call them up with the report number. That's recent enought that they probably have a little bit more information file from the inspection. They WON"T have enough to apply the current cut grading system but that tidbit is entirely possible.

There's a list of appraisers under 'resources' at the top of the page who should be able to help assign a value as it relates to a particular marketplace (insurance replacement, resale, estimated retail, etc.)

 

[beryl]

With a 3% girdle thickness (at scallops) and no culet, the pavilion slope of this stone would be 41.5 degrees.
Formula is: P = arctan[2(D-G)-(1-T)tanC] where ...
: P = pavilion slope (main facets),
: C = crown slope (main facets) = 33 degrees ,
: T = table size = .60 ,
: D = total depth = .602 ,
: G = girdle thickness (at scallops) = .03

I realize that my response, one year later, is probably academic. But the formula can be useful in future.

 

[beryl]

Error in previous reply: G = girdle thickness at POINTS (3% typical).