Crown question

[chad_c_u]

To get the crown height % for an emerald cut diamond. Do you divide by the overall width or depth of the diamond?


Chad

 

[belle]

to get the crown height, you measure with a sarin machine or similar or you have a professional examine it and give an estimate.

 

[chad_c_u]

Do you divide that height by the width or depth

 

[belle]

neither. there is more information needed if you want to ''figure'' it by numbers alone and the same machine that you would need to take those measurements, would also give you the measured crown height. at that point, there is no need for guessing. you cannot figure by depth and table alone.

 

[Paul-Antwerp]

All percentages in a fancy shape are in relation to the smallest diameter. Thus, in the case of an emerald to the width of the stone.

In rounds, the percentages are in relation to the average diameter.

Sorry Belle, but you were completely off-track here.

Live long,

 

[belle]

Date: 7/28/2006 10:51:06 AM
Author: Paul-Antwerp
All percentages in a fancy shape are in relation to the smallest diameter. Thus, in the case of an emerald to the width of the stone.

In rounds, the percentages are in relation to the average diameter.

Sorry Belle, but you were completely off-track here.

Live long,

compeletely off track? been there before!

please answer the posters question for me then.... "To get the crown height % for an emerald cut diamond. Do you divide by the overall width or depth of the diamond?"

 

[JohnQuixote]

I believe there were 2 interpretations of this question.

Belle is saying that if you don't already have the crown height you can't simply figure it using mm, depth or table%. The diamond must be physically measured to get this number.

Paul is saying that when you know the crown height the diameter is the ‘100%’ that all measurements are in relation to. With rounds that '100%' is average diameter. With emerald cuts it’s smallest diameter or width.

They are both giving correct information.

The simplest way to get the crown height % and other pertinent measurements is to have a Sarin report run as Belle suggested. 'Back in the day' Bob Hoskins, our senior gemologist, had an engineer design a crown height adaptor he could put on a leverage gauge. He could use it with the diamond and a microscope to determine height % but angles were still guesswork back then.

The great advances in non-contact measuring devices like Sarin, Helium, Ogi and Imagem have made our lives much easier.

 

[belle]

thanks for your interpretation sir john.

in regard to the original question and paul's subsequent response, i feel like i am either missing something (which is entirely possible!) or i wasn't 'compeletely' off track. i'm still hoping paul will clarify.

 

[chad_c_u]

I called some internet vendors and I have got two different answers. Blue Nile measures there diamonds according to crown height/total width. I looked at their GCAL report which determined the measurements as given. This makes since as Blue Nile''s signature collection shows 9% or above as ideal crown height. I called Good Old Gold, Ice store, and Modera and they told me the percentage was based on crown height/total depth. This would give a diamond a higher height percentage on an average basis as most stones are wider than they are deep.

My guess is the AGA charts are based on crown/depth. This would leave the Blue Nile signature collection in the AGA 1 class for crown height since a 9% height based on width would be around 14% based on depth.

I have an emerald diamond coming tomorrow with the following stats:

$6371
Weight: 1.16 ct
Measurements: 7.39x5.24x3.30
Color: G
Clarity: IF
Depth % 63.0% AGA 1A
Table % 65% AGA 1A
Crown Height% ?
Symmetry: VG AGA 1A
Polish VG AGA 1A
Girdle: Thin to Medium
Culet: None
Fluorescence: None
L/W ratio: 1.41

My hope is the crown height will fall into the 1A or 1 B category as well