Extinguishing the Fire......

[FB.]

Excuse the play on words.

Today I saw a couple of diamonds that lack fire.
I took down their GIA-cert measurements and ran them through the HCA, which agreed that their fire would be poor.

Both diamonds are very similar:

Table: 59%
Total depth: 63.2%
Crown angle: 35.5'
Pavilion angle: 41.8'

Would I be correct in making the assumption that the fire-extinguisher for these stones is mostly the (steep) pavilion angle - causing the light to strike the inside of the crown facets at a not-shallow-enough angle?

 

[strmrdr]

The crown and pavilion angle combine to send a lot of the light return and fire away from the eye.
You will see the 17% return and the 7% but the rest is not directed to your eye.

 

[strmrdr]

That crown/table doesn''t match up well with any pavilion because if you get a shallow enough pavilion to match the crown angle you get a fisheye from the larger table.
So in this case you could call it a bad crown.

 

[marcy]

Too funny on the title. Yep, you loose light and fire on too deep or too shallow of a stone.

 

[FB.]

Thanks.

Funnily enough, the diamonds seemed to have more fire with light directly pointed at the table, but viewed from an angle greater than about 45'' (as a guess), but I thought that I must have just been lucky in catching the spotlights, so didn''t consider it any further.

So does that mean that the computer models with predictions for fire, refer to the stone when viewed from directly above and that the stone could perform well when viewed by people around the wearer?

May I set out a possible scenario........

Imagine a table of four people out for dinner.
The person at the North side of the table has a diamond pendant.
An ideal diamond will direct fire at the person on the South side of the table, but not much at the East-West sides of the table?
The diamond in my opening post would split it''s fire between the people at the East and West sides of the table (and the waiter, who is viewing from a high angle, relative to the seated diners)?

In other words.....is the fire simply directed in the wrong directions (so to speak)?

 

[strmrdr]

It would depend on the angle of the lighting and the diamond but yes it would tend to be the case.
Many people when viewing a diamond on their own hand will try and move the diamond so they get the strongest return.
That is why diamonds should be looked at criticaly when shopping.
A well cut diamond will look good without having to hold ones hand just in the right spot.

 

[FB.]

Thanks, Karl.

So that us PS-ers can see the difference, would you be able to put up a side-by-side comparison of the stone that you have already modelled, against a real-world AGS-0 cert that I happened to see at the same time?

The AGS-0 had the following stats:

Table: 56.0%
Total depth: 62.1%
Crown angle: 35.1''
Crown height: 15.6%
Pavilion angle: 40.9''
Pavilion depth: 43.3%
Girdle: 1.2-3.6%
Star: 49%
Lower half: 80%
Culet: pointed


Thanks,
FB

 

[strmrdr]

You telling us your impression would be better.
There isn't a great way to model fire in one image.
I moved the ray around and posted a representative shot of what it looked like on average for where the return was going.
Doing the same for another diamond is not a direct comparison without showing you the entire range.
The primary difference would be the white light ray would be headed towards the persons eye.