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%''s vs. angles in the HCA

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Googleman

Rough_Rock
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Nov 16, 2002
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I found a stone that I really like. However, when I plug it into the HCA the cut is not what I hoped it would be. I currently only have the %'s for the crown and pavilion instead of the angles.

I do understand that inputting angles gives you a more accurate rating than inputting %'s. Should I request the angles and input those and see what happens, or will any difference only be slight and therefore I should move on with my search?

Also, is it possible for a stone to not score as well on the HCA and still look spectacular????
 

NYSP

Rough_Rock
Joined
Sep 19, 2002
Messages
6
WHY NOT? If you like the stone than buy it. Just because the HCA does not give it the best number does not indicate a poor choice.
I'm far from an expert in this field, but you cannot use the HCA as the only factor in determining your choice.
 

Rhino

Ideal_Rock
Trade
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Mar 28, 2001
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6,275
----------------
On 12/2/2002 8:05:56 PM

WHY NOT? If you like the stone than buy it. Just because the HCA does not give it the best number does not indicate a poor choice.
I'm far from an expert in this field, but you cannot use the HCA as the only factor in determining your choice.
----------------


There is truth to what you are saying and the HCA should not be the only factor but if all the information you can gather about the cut is limited to the HCA then if I were you I'd see to it that it was a nice score under 2.0 and as close to 1.0 as possible. While I have in past posts pointed out some of the weaknesses of the HCA, I would at this time emphasize the strengths of it to seperate the highly reflective, overall excellent brilliant stones from the duds.

When I am calling in stones from a supplier and I don't have all the data I look for in front of me (I actually look at star facet length, lower girdles, etc.) I can weed out right from the start what the cutter should and shouldn't send based on HCA scores. That is not the end all of my buying decision and I have turned away stones before that had scores of .5 as I use other means as well to measure and analyse light return in diamonds but if I were a consumer and wasn't employing the services of a jeweler like myself, I'd at the very least use the HCA as a help. That took Gary years of study to develope and it's advice (while I believe it should be tempered with other input) should not be discounted.

And yes ... GET THE ANGLES.

Peace,
Rhino
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
Googleman, are you talking about these proportions?

9.60 x 9.75 x 6.13mm
Table width 57%
Crown Height 15%
Pav. Depth 44.5%
 

Googleman

Rough_Rock
Joined
Nov 16, 2002
Messages
53
Yes. Those are the ones. It is actually an attractive stone in person, but not a good HCA performer. I am going to ask the broker to try and get the angles for me but I think we will end up bagging this one!
 

pricescope

Ideal_Rock
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Dec 31, 1999
Messages
8,266
Googleman, please don't get me wrong, I don't want to criticize this diamond.

All diamonds are more or less shiny. HCA penalizes diamonds that have light leakage or small spread (look smaller for its carat weight). This diamond has both.

However, it might still look very nice and you might like it more than a spready diamond with no leakage.

Can you also post the carat weight, girdle and culet please?

It should be about 3.5 carat :lickout:
 

Googleman

Rough_Rock
Joined
Nov 16, 2002
Messages
53
Leonid:

3.52 carats

E
SI1
9.60x9.75x6.13
Girdle Medium
Culet Pointed
Table Width 57%
Crown Height 15%
Pav. Depth 44.5%
(I calculated the total depth to be 63.3%--with some help! :)) )

When you plug these in it doesn't come out too good. It is a rather substanial amount of money we are considering spending, so should we ask for Sarin tests, b-scope, etc. or will this just confirm what HCA is telling us? I don't want to go through all that if we can already tell this diamond is a dud!
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
Here is DiamCalc simulation using your numbers (keep in mind crown and pavilion % are rounded so it can be slightly different).

Note: I selected HRD grading and it shows Medium girdle.

GooglemanHRD.gif
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
If we switch to AGS grading, it shows Extremely Thick girdle and AGS grade 7.

Assuming the numbers are accurate, light leakage should result in darker/duller areas underneath the table.

As you can see the spread is 6% less than for Tolkowsky cut stone.

GooglemanAGS.gif
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
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8,266
Also note that Tolkowsky cut stone of the same diameter will weight only 3.18 carat. I.e. you are getting (paying for) 0.34 crt of extra weight.[/u][/u]
 

Attachments

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
Now, interestingly enough, the diamond has not bad overall light return (except table area) and very decent contrast despite strong light leakage.

This explains why it looked nice.

I guess there is nothing wrong with buying the diamond if the price is right. After all, you can recut it later.

Hope this helps :)

GooglemanQ.gif
 

DJayNYC

Rough_Rock
Joined
Dec 2, 2002
Messages
4
Leonid,

I was wondering if there was anyway that us common, one time (hopefully) diamond buyers could run our stones through a program like those you have shown. I see that the programs are very expensive to purchase outright and would like to just run the numbers of the stone I have purchased through for curiosity's sake.

Just wondering if you knew of any way to test them online at all.

Thanks
Jay
 

pricescope

Ideal_Rock
Joined
Dec 31, 1999
Messages
8,266
Jay, you can download GemAdviser for free and play with examples included in the package. There is a good variety of crown/pavilion combinations to get an idea how you particular diamond could score.

I'm just trying to discuss and illustrate some interesting cases like this one.
 

RockDoc

Ideal_Rock
Joined
Aug 15, 2000
Messages
2,509
RE: Recutting....

Some diamonds are problematic when put back on the cutting wheel. The internal characteristics of the diamond have serious affect.

Inclusions can open, gletzes form from out of no where.

Plus - consumers need to realize that if the stone would shatter in the recutting process ( unlikely - but it happens ) the cutter ISN'T responsible and there is no insurance you can buy to insulate the consumer possibly having to sustain a hefty loss.

While recutting can be successfully accomplished there is risk with it that consumers need to be made aware of.

In addition, what about the affect of the value of the stone, if it goes below 3.00 carats?

It makes more sense to either purchase a well cut smaller stone, or a possibly well cut stone of the same weight even though it will cost more.

This consumer is considering spending a lot of money, and as such providing advice may not be the most prudent action, since you're helping the consumer make a financial decision.

Diamonds, especially ones of this size and cost need to be seen to be accurately analyzed.


It is interesting to note that the HCA reports this stone is an AGS 7?

I haven't seen many AGS 7's to tell you how different they are from the 0 grades, but it sure would be interesting to check this puppy out.

Rockdoc
 

Mara

Super_Ideal_Rock
Joined
Oct 30, 2002
Messages
31,003
Our 62% table/ 56.9% depth/ 29.9 crown angle diamond is rated an AGS 7 both on Leonid's DiamCalc findings, and on the sarin report we got with the diamond. However, it's brilliant and definitely gorgeous..and it got AGS 0's on the depth % and pavilion angle, and an AGS 3 on the table. The AGS 7 was for the shallow crown angle. Kind of interesting to read this thread and see the AGS 7 number popup--hey I recognize that! :)

So when a diamond such as mine gets 0's, a 3, and a 7, how does it end up with the total rating of AGS 7? Is it just that AGS takes the worst score and slaps that rating on the diamond? A little misleading if that's the case? I've been wondering this..now seems like a good time to ask!:bigsmile:
 

Serg

Ideal_Rock
Trade
Joined
Mar 21, 2002
Messages
2,535
----------------
On 12/3/2002 10:22:50 PM

RE: Recutting....



In addition, what about the affect of the value of the stone, if it goes below 3.00 carats?


Rockdoc


----------------


Reduction of a angle of pavilion by 1 degree will give reduction of weight of this stone of 0.06 carats only!!
It will 3.40-3.47 ct after good recutting
 

Serg

Ideal_Rock
Trade
Joined
Mar 21, 2002
Messages
2,535
----------------
On 12/3/2002 10:22:50 PM

RE: Recutting....



Plus - consumers need to realize that if the stone would shatter in the recutting process ( unlikely - but it happens ) the cutter ISN'T responsible and there is no insurance you can buy to insulate the consumer possibly having to sustain a hefty loss.

While recutting can be successfully accomplished there is risk with it that consumers need to be made aware of.


Rockdoc


----------------


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Post 15 - #220204 12-03-02 10:45 AM
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Don't be too afraid of your diamond shattering...
Given that your existing diamond has already survived the cutting process once and has survived the intense pressure when it was formed deep within the earth millions of years ago and the trauma of making it to the surface, it is not very common for recuts to break on the wheel.

Yes it does happen sometimes, but in all the diamonds I've ever had recut, it's only happened to me once.

Sometimes there are certain features, such as internal graining, that might make you choose not to attempt a recut, and those are things that the diamond cutter can advise you on.

You might check with your insurance agent to see if something like this might be covered, and then you'd have all the bases covered.

Jay
 
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