how high a crown is too high? round vs EC

[windowshopper]

I love a high crown on a stone provided it doesnt take too much of the spread away................so is the effect on spread the main concern with a high crown?

 

[valeria101]

It is not unthinkable to find crown heights over 20% on some Asschers and definitely on the older stones. Lucida and the Royal Asscher have very high crowns ( = more than the 15%-ish of the rounds) too. I guess spread is the main concern. Not sure if there is a definite "too much" from the optics point of view - this one is a Q for Garry

Below is the profile of an old asscher case in point, I think.

 

[windowshopper]

thanks for the gorgeous photo! what a knockout stone. yes i was curious if the main issue was spread or something affecting optics etc

 

[strmrdr]

Too high a crown and it mirrors badly from off angle.
Durability becomes an issue also.

 

[windowshopper]

i can see that...especially durability...........more sticking out to bang

 

[strmrdr]

Date: 1/15/2005 3

7:22 PM
Author: windowshopper
i can see that...especially durability...........more sticking out to bang

yep.
Also cleavage planes come into play.
More chances for a hard knock to hit on one and shear a section off.

 

[Garry H (Cut Nut)]

Too high a crown like that asscher and as much light goes in and out the pavilion as the crown because the stone is nearly the same from both sides - make sense?

But when you have that much stone sticking out the top - it has less width but more length (oops I meant height

.

So what sort of "size" do you perefer?

This stone has a small spread but very good light return and amazing fire:-

 

[windowshopper]

well i have antique cushion earrings with depths of 78/79 with astounding fire? (not sure of the word) and I like the high crown but I am thinking of more in the 16/17/18 range not 20 +

does a higher crown cause a more prismatic (sp?) effect since your have the pyramid coming out both sides of the girdle as opposed to mainly the bottom?

make sense??????????????? didnt think so,................

 

[valeria101]

Garry, quite often is said that "high crown = more fire" - what''s the proper explanation from that ?

Higher crown angles bend light away from the front viewer... but why does this make dispersion more visible ?

 

[Michael_E]

Optically, high crown angles show more fire because the majority of the light is hitting the entry and exit facets at a lower angle which causes the "spread" of colors derived from white light to be greater.
I don''t mean to butt in here, so I''ll let Gary go further into this. I do have one question for you Gary. Where did you get that rendering of the diamond ? It''s just beautiful ! I am putting together some images to import to my CAD program and I would dearly love to be able to model stones of different shapes from different angles, (the CAD program, Rhino 3D has produces slow and very poor images on stones, but I can import them). Do you have a particular program that is used for that and is it generally available ?

 

[valeria101]

Date: 1/15/2005 4

5:30 PM
Author: Michael_E

Rhino 3D has produces slow and very poor images on stones, but I can import them). Do you have a particular program that is used for that and is it generally available ?

This comes form the Gem Adviser reder on Good Old Gold... looks pretty close to me

although the professional software can produce somewhat better resolution.

 

[windowshopper]

soooooo--would a higher crown producing more fire have more color play and be a less "white light" diamond?

 

[windowshopper]

is the pavillion the measurement of the stone from the girdle to the culet?

 

[kevinraja]

Yep