Garry, why can''t HCA be used as a rejection tool for Solasfera or modified round brilliant

[stone-cold11]

By modified round brilliant, I am considering only stones with un-modified main pavilion and main crown facets, such as solasfera. If they are measuring the same numbers, so why can''t the HCA be used as a rejection tool in this case? Other than when you are designing the HCA using modern round brilliant and do not to generalize, the physic involves should be the same except for the greater number of facets involve, probably a lower cut off score might be required.

https://www.pricescope.com/community/threads/hca-vs-solasfera-vs-ags0.77185/

Thanks.

 

[strmrdr]

The relationships between the mains and lowers vs crown and each other is changed which changes how the pavilion works.
When you change the pavilion structure the angles change also.
For example a single cut with a pavilion angle of an ideal cut RB is a dud.
This single cut aset is a 34.5 crown and a 40.8 pavilion which would be top angles in a RB.

 

[stone-cold11]

But that would mainly mean the shifting of the score threshold right? For you example, single cuts would shift higher in the crown to pav relationship (HCA = 2.5-3) and solasfera a lower crown pav relationship (HCA ard 1). Just not documented?

I know it is not hard and fast rule, just trying to understand.

 

[strmrdr]

Date: 9/4/2009 5:30:12 PM
Author: Stone-cold11
But that would mainly mean the shifting of the score threshold right? For you example, single cuts would shift higher in the crown to pav relationship (HCA = 2.5-3) and solasfera a lower crown pav relationship (HCA ard 1). Just not documented?


I know it is not hard and fast rule, just trying to understand.

depends on the structure
There is no rule
I have seen extra facet rounds go both ways.
The ones that get produced are more likely the ones that stay around RB territory or deeper.
If I remember right most of the solasfera are on the steep pavilion side with shallower crowns.

 

[strmrdr]

This has a lot to do with why they can have steeper pavilions:
http://journal.pricescope.com/Articles/68/1/Do-the-pavilion-mains-drive-light-return-in-the-modern-round-brilliant.aspx

The halves are at a shallower angle in relation to the mains compared to a RB so they can use deeper mains without leakage.
Then you break up the directional nature of such a pavilion with more crown and pavilion facets and smaller virtual facets.
It is an interesting case study
It does explain however why it dazzles the b-scope into uselessness lol

 

[Garry H (Cut Nut)]

i believe you could always get an ideal-scope image or an opinion from someone trustworthy looking thru a scope on these stones - so why bother with hCA?

 

[Rhino]

Good points. I would argue the same would hold true however for other certain 57 faceted diamonds, particularly those with short lower halves like OEC's. The HCA I know is not reliable for those as well.

 

[strmrdr]

Date: 9/5/2009 12:43:28 AM
Author: Rhino
Good points. I would argue the same would hold true however for other certain 57 faceted diamonds, particularly those with short lower halves like OEC''s. The HCA I know is not reliable for those as well.

true