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Angles determined from percentages

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ian74

Rough_Rock
Joined
Jan 28, 2003
Messages
1
Hi, I''ve been lurking here for a few weeks now and decided to register to ask for help regarding a certain stone

I have been shopping around for a diamond for the most wonderful girl in the whole world. I went to a small independent jeweler, and was offered a really beautiful stone at what seems to me to be a reasonable price. I''ve been shopping for a small .5ct stone, because my girl has tiny fingers, and I''m also quite poor.

EGL cert. (NY)

.61 ct. round brilliant
color: E
clarity: VVS2
table: 63%
depth: 59.1 %
crown: 12%
Pavillion: 43%
Girdle, thin to medium faceted


Price was 2000. I ran the numbers through the HCA and it was initially a 1.5. However, within the last couple of days it seems to have downgraded into a 2 (i guess it was finetuned, or I consistantly entered the wrong numbers).

Anyway, I read that the percentages were useless for the most part. So I wondered if I can use the percentages, to determine the height of the crown/pavillion in millimeters, knowing the stone dimensions, and then use some trigonometry to determine the angles. Now I did it, and I determined the angles to be:

Crown: 33.1 degrees
pavillion: 40.6 degrees.

It seems like a logical approach, but is this reasonable? HCA still gives me a 2 with these angles. If I change the function I use to determine the angles such as inverse tan. vs. inverse sin, I get slight variation in the angles that can drop it to a 3.6 on the HCA with a potential fish eye. So I don''t know if I''m off or not. My girl loved it when we were shopping, it was really the brightest stone we had seen yet. Certainly in the price range of a starving grad student as well.

Could someone plug it into that diamcalc program for me? As a favor for a newbie?

What is everybodys thought on this stone? Any opinions will be much appreciated.
 

Giangi

Ideal_Rock
Joined
Jan 23, 2003
Messages
2,530
Usually a good way to find out crown height is:
Crown height percentage : (100 - Table size)
Or in your case:
12 : 37 = 32.4'

This is the formula I use.
Hope it helps.
BTW the cut isn't so great and most important be VERY careful of EGLs grades and get the stone checked by an appraiser.

Giangi
 

ccuheartnurse

Brilliant_Rock
Premium
Joined
May 22, 2002
Messages
1,734
Ian, I know someone will say this sooner or later, but why go for a VVS1 if cost is a consideration? For a .5 stone or even larger, an ideal SI-1 will be a great stone & you may in fact get something bigger for your money. Not only about size, but even going to an F colour stone (if you notice colour) might also be a reasonable trade-off. You might want to check out Jonathan at Good old Gold or Jan & Diamond Brokers of Florida (this is where I went) for your purchase. They both have a 100% trade-up policy as that might be an option for you in the future.

Judy
:)
 

ccuheartnurse

Brilliant_Rock
Premium
Joined
May 22, 2002
Messages
1,734
Ian,
Go to diamondbrokersofflorida.com. I just plugged in what you're looking for & Jan has quite a few ex/ex, vg/vg or ideals in the .5 range for the same money you're spending on that stone with a large table & shallow depth. Why not get an ideal stone for that money? Makes sense.

Judy
:)
 

Giangi

Ideal_Rock
Joined
Jan 23, 2003
Messages
2,530
Judy, I thought the same exact thing... Great minds think alike
!!!

I just checked whiteflash.com and I found quite a few nice diamonds:
a) 0.63 G SI 1 AGS 0 H&A $1918
b) 0.60 G SI 1 AGS 0 H&A $1827
c) 0.67 I VS 2 AGS 0 H&A $1690
d) 0.49 E VS 1 AGS 0 H&A $1955
e) 0.50 E SI 1 AGS 0 H&A $1890
f) 0.60 F SI 1 AGS 0 H&A $2079 (there are two stones, one is 0.600, while the other is 0.604)

On superbcert.com there is a ton of diamonds within your price range...
All of these stones have a much better make and are GIA/AGS graded, which are far stricter than EGL NY.

Giangi
 

Mara

Super_Ideal_Rock
Joined
Oct 30, 2002
Messages
31,003
I think there were modifications made to the HCA recently as my stone as well has different return #'s. Would be nice if Garry can confirm and in the future also post something to let people know when the last update was so that people in the midst of considering stones do not get confused when their #'s change, etc.
 

Richard Sherwood

Ideal_Rock
Joined
Sep 25, 2002
Messages
4,924
Ian, when I ran it thru the DiamondCalc I came up with 33.04 crown angle and 40.7 pavilion angle. Your estimations were pretty good.

My computer's running slow, so I didn't get the light return analysis, but I'll post an IdealScope computer simulated image for you.

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 simulation is reproduced best when the actual diamond is being viewed and the image "tweaked" to the appearance of the diamond. However, this "blind" reproduction should be fairly close on the major points.

0.61.jpg
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
14,926
Yes Mara there have beeen some mod's, and no this stone would not be affected


The other prob with the %'s is they are rounded to whole #'s so what if it was really 12.6% or 13.4% crown height.
The %'s can help you get an idea if the stone is worth asking for a Sarin report on


Definetly avid VVS if you want to buy on a budget, unless you are buying for religious purity reasons.
 
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