Why does this stone lack scintilation?

[MrsT]

I''m one of those people that''s just not going to get the scienctific explanations, so try to bear with me.I can imagine how dumb my questions sound. For me, a beautiful diamond should have excellent/very good light performance. Correct me if I''m wrong, but return of white light and colorlerd light is the movement - or scintilation/sparkle of a diamond.

So why did the following stone seem so dull in the store. Most of the measurements fall into the American Ideal range except the crown angel.

HCA score 1.3 TIC

7.67 x 7.70 x 4.76

GIA cert.
1.72 G SI1 (pin points under microscope)
Cut Grade: Excellent
Polish/Symmetry: Both Excellent
Table: 55% (Class 1A American Ideal)
Depth: 61.8% (Class 1A)
Pav.Depth: 42.5% (Class 1A)
Crown Height: 16.0% (class 1A)
Crown Angle: 35.5 (class 2A)
Pav.Angel: 40.6
Girdle:thin-med (Class 1A)

$15,000

Is there anything here that would explain the lack of scintilation?

Second question:
Is the HCA tool the only way to tell if tables/depths are in the proper proportions? If a table is 58% is there a way to know the most optimal depth for a stone cut with that table?
Or do you just have to run the numbers in HCA to tell you that? I''m going to see a stone today that the jeweler claims is unbelievable and scored 2.0 on HCA. The table is 58% and depth 62.5 , Crown A:34.4 and Pav.A 41. He has the Sarin report.


Thanks,
Mrs.T

 

[Cehrabehra]

Date: 7/19/2006 9:05:31 AM
Author:Mrs.T

Second question:
Is the HCA tool the only way to tell if tables/depths are in the proper proportions? If a table is 58% is there a way to know the most optimal depth for a stone cut with that table?

Thanks,
Mrs.T

Ooooh... I want to know the answer to that question myself! If not a tool - how about a table of corresponding ideal t/d proportions using a standard girdle size?

 

[JulieN]

return of light is scintillation.

to get scintillation, either you move, the diamond moves, or the light moves.

Go to HCA, 60 D, 58T, 34.5 C, 40.7 P. Wow, 1 TIC. Anyway, you can print out the chart...might need an image editor to get the numbers on the axis to come out nicely. If it falls inside the white, solid outline, or just a little to the left of the outline, that means that the angles work.

 

[JulieN]

Date: 7/19/2006 9:20:43 AM
Author: Cehrabehra

Ooooh... I want to know the answer to that question myself! If not a tool - how about a table of corresponding ideal t/d proportions using a standard girdle size?

Depth is a factor of HCA (which assumes medium girdle.) Only knowing depth and table is pretty useless.

 

[belle]

depth and table play a part in the whole picture but they are not as important (alone) as the crown and pavilion angle working together. you can have a 57% table and several combinations of c/p angles that work within that range. as you start to get out of a certain range with the c/p, the angles no longer work well (for good performance) in that combination. that is basically what the hca is telling you. with a given depth/table, there are a certain range of angles that work well. of course, hca cannot add in the (huge) factor of optical symmetry and minor facet configuration which plays a big part on the way you see ''sparkle'' (scintillation) coming off of these facets.

 

[Cehrabehra]

Date: 7/19/2006 9:30:00 AM
Author: JulieN

Date: 7/19/2006 9:20:43 AM
Author: Cehrabehra

Ooooh... I want to know the answer to that question myself! If not a tool - how about a table of corresponding ideal t/d proportions using a standard girdle size?

Depth is a factor of HCA (which assumes medium girdle.) Only knowing depth and table is pretty useless.

Agreed, but if there were a standard girdle thickness, you''d see an ideal corelation between the angles that I''m pretty sure would convert to a larger stone with the same girdle thickness. Change the girdle thickness, change the angles - yes... but understanding that correlation could be useful. I''m sure there is a basic principle that describes the angle that facets be from one another regardless of the girdle. Like for example a non-existent girdle.. there would be ideal angles for that in any sized stone. Shave off the edge and you have a girdle that is however wide depending on what is removed, and the angles within the stone are still performing at that same angle ideal, but the technical angle of the cut from the bottom and top of the girdle would be different. I hope that made sense LOL

 

[MrsT]

I just got back from viewing the diamond that scored 2.0 HCA that the jeweler said was amazing.

I wasn''t happy and I''m still not sure my judgement is to be depended on.

This was a wierd experience and I don''t think I''m going back to this jeweler in the future.

He showed me a "blurry" (fax) copy of the GIA and clear copies of the Sarin report he was nice enough to request for me.
The Sarin doesn''t agree with the GIA in it''s assessment of symmetry.

I only noticed this because there was a bright white pin point of light where the culet is. In addition to that, this pin point of white light looked off-center to my eye. That made me look at the Saring closer.

The Sarin gave Very Good scores under symmetry and I noticed the Culet was off but I can''t believe I would notice that! I think I''m imagining it. The GIA said the culet was off center by 0.3
Anyway, how can the GIA report claim this is an excellent cut, excellent polish,excellent symmetry when the Sarin doesn''t agree?

Mrs.T

 

[MrsT]

I''m bumping this post in the hopes that someone can comment on my last message about conflicting Sarin/GIA.

Hope that''s o.k.
Mrs.T

 

[Richard Sherwood]

Hi Mrs T. With the technology currently available, measuring devices are usually close but not identical in their measurements. You''ll almost never find two machines (or humans) coming up with the exact same measurements on everything. Close enough to be considered "precise", but not "exact".