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What''s wrong here??

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djgaloot

Rough_Rock
Joined
Apr 16, 2003
Messages
56
I am "practice shopping" and getting used to specs and terminology in preparation for my real purchases. Please help me out with understanding the following:

.33ct
diam 4.44
total depth 62.4%
crown angle 35
crown height 15.4%
Pavil angle 41.5
pavil depth 43.5%
culet .5% v small
table size 55.9%
girdle 1.7%

All seems within ideal specs or very close

GIA
depth 62.8%
table 56%
symmetry very good

HCA 5.4
light return Good
Fire Fair
Scintillation Fair
spread very Good

Why such a low rating on HCA? without the HCA I may have considered this diamond.
 

Rank Amateur

Brilliant_Rock
Joined
Feb 26, 2003
Messages
1,553
I'll bump this up so that one of the pros can answer, but I'm guessing that this is the classic "steep-deep" combo that the HCA tries to weed out.

The net effect is still a good diamond - just not a great one (according to the HCA). Your eyes may tell you differently.
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
Djgaloot,

As RA wrote, 35° and 41.5° crown and pavilion angles is deep/steep combination causing light leakage

My only concern is how accurate your Sarin (or Megascope?) data are because 41.5° pavilion angle along with 0.5% culet gives 44% pavilion depth, not 43.5%.

43.5% pavilion depth and 0.5% culet correspond to 41.2° pavilion angle. Still deep but not as much as 41.5°.

Plugging 43.5% pavilion depth will give you 3.4 (Very Good) HCA.
 

Rank Amateur

Brilliant_Rock
Joined
Feb 26, 2003
Messages
1,553
Hey leonid!

If this one is steep-deep why is the spread still "very good"? Maybe I need to do some trig, but I thought that steep and deep yields a small diameter for a given weight thereby reducing the apparent "spread".

Of course I could have this totally wrong.
 

djgaloot

Rough_Rock
Joined
Apr 16, 2003
Messages
56
RA, Thanks for the bump up.

Lenoid,
I don't know the accuracy of the data. It was off a sarin report with the diamond. Here is a bit more specific data relating to symmetry:
crown angle 34.4-35.8
crown height 15.2-15.5
P angle 41.1-41.9
P Depth 43.2-43.8
table size 55.7-56.2
girdle 1.3-2.1
 

djgaloot

Rough_Rock
Joined
Apr 16, 2003
Messages
56
Lenoid,
I plugged in all the data as %'s into the HCA and it gave a result as 3.0
VG
VG
G
VG

In a case such as this, if I was interested in the stone, would I ask to have it re-analyzed?

dave
 

Richard Sherwood

Ideal_Rock
Joined
Sep 25, 2002
Messages
4,924
-----------
I'm guessing that this is the classic "steep-deep" combo that the HCA
tries to weed out.
-----------

Ah yes Rank, the mother and father of the dreaded "ring of death". A crown angle just a little bit too steep, combined with a pavilion angle just a little too deep, creates an area of light leakage just inside the table that Rhino dubbed the "ring of death".

That's what's dragging those performance figures down Dave. I've attached a DiamCalc computer simulated IdealScope image showing the light leakage as a white "ring" just inside the table. I'll follow that with a photoreal image showing how the light leakage translates to a dark area when viewed naturally.

In my opinion, the effect is more dramatic in the images than it is in real life. If you really know what you're looking for you'll spot it. Otherwise you'll gaze at it and say, "Wow, what a pretty diamond". It's only when you start heading down cut geek road that it starts to bother you.
 

Richard Sherwood

Ideal_Rock
Joined
Sep 25, 2002
Messages
4,924
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IdealScope- In general, the darker pink areas indicate areas of greater light return, with the lighter pink areas indicating areas of lesser light return. The black areas indicate areas of greater contrast, with the gray areas indicating areas of lesser contrast. The white areas indicate areas of light leakage. A good explanation of the IdealScope image along with examples can be found at https://www.pricescope.com/idealscope_indx.asp

Disclaimer- The facet arrangement and symmetry of the image will probably vary from your actual diamond, which may affect the light performance indicated. The computer generates an image with “perfect” symmetry, which is rare. Also, the star/lower girdle facet lengths may be different from your diamond. The computer simulation is reproduced best when the actual diamond is being viewed and the image "tweaked" to the appearance of the diamond, or Sarin info is downloaded directly into the program. However, this "blind" reproduction should be helpful in considering the major light performance aspects.
-----------
 

djgaloot

Rough_Rock
Joined
Apr 16, 2003
Messages
56
Richard,
Thanks for the images and explaination. I'm slowly learning more than I thought I'd ever need to know! See my new post on HCA credence. Perhaps you could give insight there also?
thanks so much,
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
RA, I played with the diameter and spread - I don't know. I have a feeling that the Sarin data are not very accurate. The reason could be that this is a small stone one should use special set of lenses to get maximum accuracy. I also wonder whether it was Diamention or BrilliantEye.
 
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