If I''m being specific about what I want in a diamond, is this enough?

[BigToque]

Round Brilliant
1.ct
F
VS2
Depth %: 59
Table %: 55
Crown Angle: 34.5
Pavilion Angle: 40.5
Culet: None
Flourescence: None
Girdle: 1.5% (medium), faceted
Polish: Ideal
Symmertry: Ideal
H&A

My next question is, would you think this was a good diamond? How could it be made better? HCA gives it a .2 within TIC.

 

[valeria101]

Is there such a thing ?

Any reason why the specs have to be this much and nothing else ? The usual H&A standard sound strict enough as is... this is allot more over the top !

... ohn the other hand, specifying an average for the angles does not pin down one usual requirement for those "superideals" - optical symmetry. And there's no way to describe it properly by the numbers. This is why H&A viewes and pictures are out there.

 

[hoorray]

I think a range of specs is a more reasonable thing to define, as there are many beautiful stones out there with variable specs, just within a tight range. When my DH was looking, NiceIce posted these specs as a "tight" range for a super ideal.

The Niceice "tight" specs were:
Depth between 59 - 61.8%
Table diameter between 55 - 56%
Crown angle between 34.3 - 34.8 degrees
Pavilion angle between 40.6 - 40.9 degrees
Girdle: thin to medium, faceted or medium, faceted
Culet: GIA None or AGS Pointed
Polish: GIA Excellent or AGS Ideal
Symmetry: GIA Excellent or AGS Ideal

The specs you posted are in the shallow end of this range, thus the very low HCA score. Many people try to optimize for around 1.0 on the HCA scale, but anything below 2.0 is considered a potential top performer. (The HCA is a tool to use to eliminate stones, not select them. It doesn't profess to be specific enough to differentiate significantly below 2.0. ) Those stones scoring in the .5 or less range can be shallow and subject to dark spots from head shadow. Do a search to read about this -- Garry has written about is several times.

 

[Regular Guy]

OK, Ana helped me get it. BT, I had to check the numbers, because I haven't seen a .2 show up here yet. But, I'm guessing you haven't either...you're trying to craft a diamond's ideal numbers, aren't you.

If that's you're agenda, you may do better by following the formula that's been explicated by the likes of NiceIce (while writing, Lop's posted them above) and others here, where their agenda is to identify defining angle ranges, and have their picks fall within them. You can probably use Dave Atlas' AGA 1A to accomplish a similar purpose. Despite my own dogmatic literalist approach to these things, you have to give the author his due. Garry's intent (he's probably around here now) is to open things up, rather than narrow them down. The big red area on the chart is designed to describe the wide range of optimum possibilities. Although you could give a jeweler you're working with the set of numbers you've crafted above, you'd probably be constraining yourself more than necessary in doing so. Frankly, if you'd like to craft an optimum set of numbers, you might try to figure out those datapoints that are specifically, today, not AGS0, but still get you 4 excellents...thereby getting you the goods, and saving you some money, both.

 

[BigToque]

Thanks for the replies...

I was basically trying to look for an ideal set of numbers. This range that was posted was what I have written down on a piece of paper and it''s probably what I''ll use when I''m looking around. What I posted was just the highest rated stone I could get on HCA.

 

[Dancing Fire]

Date: 4/27/2005 6:42:24 PM
Author: lop
I think a range of specs is a more reasonable thing to define, as there are many beautiful stones out there with variable specs, just within a tight range. When my DH was looking, NiceIce posted these specs as a ''tight'' range for a super ideal.

The Niceice ''tight'' specs were:
Depth between 59 - 61.8%
Table diameter between 55 - 56%
Crown angle between 34.3 - 34.8 degrees
Pavilion angle between 40.6 - 40.9 degrees
Girdle: thin to medium, faceted or medium, faceted
Culet: GIA None or AGS Pointed
Polish: GIA Excellent or AGS Ideal
Symmetry: GIA Excellent or AGS Ideal

The specs you posted are in the shallow end of this range, thus the very low HCA score. Many people try to optimize for around 1.0 on the HCA scale, but anything below 2.0 is considered a potential top performer. (The HCA is a tool to use to eliminate stones, not select them. It doesn''t profess to be specific enough to differentiate significantly below 2.0. ) Those stones scoring in the .5 or less range can be shallow and subject to dark spots from head shadow. Do a search to read about this -- Garry has written about is several times.

yeah.... i would prefer a stone more closer to 1.0 HCA.

 

[Lord Summerisle]

I would say on the question of are you being too specific.

Yes and No.

Tho I’ll vague that up a little for you.

If you are prepared to possibly wait for eternity for a diamond that meets every exact criterion on that list then no. (And even then it wouldn’t be exact as the crown and pav angles would be averaged at 34.5/40.5 rather than dead on those numbers)

If you where to say… well this is what I would ideally like, but I will consider stones that come very near to it…

1ct. being such a magic figure in terms of pricing a lot of stones get cut slightly deeper to get them to click over into the 1ct range, where as if they where left at 59% would come in at the lower prices .9-.99ct range. And doesn’t make good business sense in that respect.

A quick look on PS showed up just over a dozen stones F VS2 in a search of .9-1.1ct of which none where below 1ct and of them only 2 stones came in with a depth of below 60.5% one at Good Old Gold (1.1ct/60.4%/57.5%/35/40.7/6.50-6.53/3.94/HCA 1.5) - http://www.goodoldgold.com/1_01ct_f_vs2_h&a5.htm and the other at Whiteflash (1.0ct/60%/55%/34.7/40.6/6.51-6.53/3.91/HCA 0.6) - http://www.whiteflash.com/diamonds/diamond_Details.aspx?itemcode=AGS-5916205# Both are H&As.

As for clarity... the GoG has an inclusion under the table, WF an inclusion under one of the upper girdle facets. Tho I doubt if you’ll spot either of them anyway unless using magnification. Both are around $8k.

Personally i lean towards the WF stone in this instance, but the GoG is a hair split away - but only since it is that little tiny weeny bit cheaper - 7.7K with a bank wire compared to GoG's 8.1K full price.

 

[Paul-Antwerp]

Date: 4/27/2005 6:11

8 PM
Author:BigToque
Round Brilliant
1.ct
F
VS2
Depth %: 59
Table %: 55
Crown Angle: 34.5
Pavilion Angle: 40.5
Culet: None
Flourescence: None
Girdle: 1.5% (medium), faceted
Polish: Ideal
Symmertry: Ideal
H&A

My next question is, would you think this was a good diamond? How could it be made better? HCA gives it a .2 within TIC.

To start, I think that with these angles and table size, you can never arrive at a depth of 59%. It should be at least around 60% for a real stone.

Then, you make the mistake of only taking HCA as your tool of selection. The HCA is not designed for this purpose. It is a sorting tool, with which you can eliminate known bad performers. A good HCA-score means that this stone is ''potentially'' a stone with high light performance, but one needs other tools and finally visual verification to assess a stone further.

In this case, you managed to get the best possible HCA-score, but this brings about specific problems. To start, the HCA favours spready stones, and in this case, you managed to get the maximum score because it regarded the stone as having almost no girdle thickness.

More importantly, the best performing combinations of proportions in all gemstones (not only diamonds) are known to be very close to an area where the light performance drops dramatically. This was first shown in the studies of Bruce Harding, who occasionally posts here as ''beryl''. In this case, this combination is extremely close to where the light performance drops.

In the future AGS-system, this combination is AGS-0, but at the edge of an area where the grade becomes AGS-2 or AGS-3. The cutter will have to cut an extremely symmetrical stone with these parameters, in order to obtain that AGS-0-grade.

In the new GIA-system, there is a high probability of this stone not getting the best grade of Excellent, but that of Very Good instead, for the same reason. Since their new system is based upon observations of real diamonds, and since it is highly unlikely that they will have observed a stone with these exact average parameters, which also has this extreme optical symmetry, it is very likely that this stone automatically gets downgraded in their future system.

The major lesson is that you have to use the HCA for its purpose. If you use it like you do, you are likely to get a stone with lower light performance, than you want. The other posters are therefore absolutely right in advising you to broaden your criteria.

Live long,

 

[Regular Guy]

Date: 4/28/2005 6:51

6 AM
Author: Paul-Antwerp

Date: 4/27/2005 6:11

8 PM
Author:BigToque
Round Brilliant
1.ct
F
VS2
Depth %: 59
Table %: 55
Crown Angle: 34.5
Pavilion Angle: 40.5
Culet: None
Flourescence: None
Girdle: 1.5% (medium), faceted
Polish: Ideal
Symmertry: Ideal
H&A

My next question is, would you think this was a good diamond? How could it be made better? HCA gives it a .2 within TIC.

Then, you make the mistake of only taking HCA as your tool of selection. The HCA is not designed for this purpose. It is a sorting tool, with which you can eliminate known bad performers. A good HCA-score means that this stone is ''potentially'' a stone with high light performance, but one needs other tools and finally visual verification to assess a stone further.

I think the subtle language question here...whether the HCA is a sorting or selecting tool, should reasonably be associated with odds making. Presumably we are not talking about coin flipping here. Paul, or others experienced in these things...if there is simply a really very high probability that a diamond with a good HCA of 0 - 2 will be the one you want for optimal light performance...we need to call this a selection process, that further needs to be confirmed...alone. Alternately, if there is a good frequency (you name it?) of cases in which a diamond with a good HCA score will be one we''ll need to pass on for not after all performing the way we would like, it then becomes the sorting tool described here.

So, gentlemen, which is it? Why could be helpful, buy which is OK.

Many thanks.

 

[Garry H (Cut Nut)]

BT you have been told the truth from many good people.

Use HCA for rejection, not selection.

And Paul is correct - you can model a stone proportions with a negative girdle - but you cant find any - so it is not a problem of the software - but a missuse of it.

Those proportions can have 60.1% depth for a thin girdle.

 

[strmrdr]

Date: 4/28/2005 7:15:36 AM
Author: Regular Guy

Date: 4/28/2005 6:51

6 AM

Author: Paul-Antwerp

Date: 4/27/2005 6:11

8 PM

Author:BigToque

Round Brilliant

1.ct

F

VS2

Depth %: 59

Table %: 55

Crown Angle: 34.5

Pavilion Angle: 40.5

Culet: None

Flourescence: None

Girdle: 1.5% (medium), faceted

Polish: Ideal

Symmertry: Ideal

H&A


My next question is, would you think this was a good diamond? How could it be made better? HCA gives it a .2 within TIC.

Then, you make the mistake of only taking HCA as your tool of selection. The HCA is not designed for this purpose. It is a sorting tool, with which you can eliminate known bad performers. A good HCA-score means that this stone is ''potentially'' a stone with high light performance, but one needs other tools and finally visual verification to assess a stone further.

I think the subtle language question here...whether the HCA is a sorting or selecting tool, should reasonably be associated with odds making. Presumably we are not talking about coin flipping here. Paul, or others experienced in these things...if there is simply a really very high probability that a diamond with a good HCA of 0 - 2 will be the one you want for optimal light performance...we need to call this a selection process, that further needs to be confirmed...alone. Alternately, if there is a good frequency (you name it?) of cases in which a diamond with a good HCA score will be one we''ll need to pass on for not after all performing the way we would like, it then becomes the sorting tool described here.


So, gentlemen, which is it? Why could be helpful, buy which is OK.


Many thanks.

I look at it as a sorting tool to select the diamonds to take a closer look at.
The hca uses averages and makes some assumptions about the diamond that may or may not be true.
The average might be good but the range bad and the stone a dog.
This was talked about by niceice a while back in that they were seeing stones with one facet cut way out from the others to bring the average into the ags0 range.
The new ags0 by the sounds of it should be better at catching this and down grading them accordingly.
The same stones will fool the hca and until the hca considers all facets instead of the averages they will continue to do so.
The problem is that the hca will then lose its ease of use.

So like the rest of the tools available the hca will remain one piece of the puzzle but not the whole picture.

 

[Paul-Antwerp]

Date: 4/28/2005 7:15:36 AM
Author: Regular Guy

I think the subtle language question here...whether the HCA is a sorting or selecting tool, should reasonably be associated with odds making. Presumably we are not talking about coin flipping here. Paul, or others experienced in these things...if there is simply a really very high probability that a diamond with a good HCA of 0 - 2 will be the one you want for optimal light performance...we need to call this a selection process, that further needs to be confirmed...alone. Alternately, if there is a good frequency (you name it?) of cases in which a diamond with a good HCA score will be one we''ll need to pass on for not after all performing the way we would like, it then becomes the sorting tool described here.

So, gentlemen, which is it? Why could be helpful, buy which is OK.

Many thanks.

The HCA is a sorting tool, not a selection tool. Like storm said, because it uses averages of main facets only, the result is still rather rough, and not at all sufficient to base a selection on it.

The nice thing is that it clearly weeds out all the sure bad performers. It is impossible for a round stone to have bad averages of main facets, and still, because of the asymmetry and/or the minor facets, be a stone with high light performance. The main angles are comparable to the foundations of a house, and with bad foundations, it is impossible to build a solid house. However, good foundations do not guarantee that the rest of the house will be built according to standard.

Live long,

 

[aljdewey]

Date: 4/27/2005 9

7:47 PM
Author: BigToque
What I posted was just the highest rated stone I could get on HCA.

But that''s just the problem....it''s not the "highest rated" stone.....0.2 is not a "better" score than 1.7, for example.

As long as it''s under 2.0 - it''s fine.

 

[Regular Guy]

So...if trying to keep it simple...

Date: 4/28/2005 12:52:19 PM
Author: Paul-Antwerp

Date: 4/28/2005 7:15:36 AM
Author: Regular Guy

I think the subtle language question here...whether the HCA is a sorting or selecting tool, should reasonably be associated with odds making. Presumably we are not talking about coin flipping here. Paul, or others experienced in these things...if there is simply a really very high probability that a diamond with a good HCA of 0 - 2 will be the one you want for optimal light performance...we need to call this a selection process, that further needs to be confirmed...alone. Alternately, if there is a good frequency (you name it?) of cases in which a diamond with a good HCA score will be one we'll need to pass on for not after all performing the way we would like, it then becomes the sorting tool described here.

So, gentlemen, which is it? Why could be helpful, buy which is OK.

Many thanks.

The HCA is a sorting tool, not a selection tool. Like storm said, because it uses averages of main facets only, the result is still rather rough, and not at all sufficient to base a selection on it.

The nice thing is that it clearly weeds out all the sure bad performers. It is impossible for a round stone to have bad averages of main facets, and still, because of the asymmetry and/or the minor facets, be a stone with high light performance. The main angles are comparable to the foundations of a house, and with bad foundations, it is impossible to build a solid house. However, good foundations do not guarantee that the rest of the house will be built according to standard.

Live long,

I will confess having some of the same concerns Nerdbot recently confessed, at picking well...based on my eyes, anyway. So, if trying to keep it simple, to what extent is there agreement that, having sorted with the HCA, then using a tool such as the idealscope, perhaps coupled with an H&A viewer (used only if only the expectation of H&A is present?) would be sufficient to make what an expert could be expected to regard an an ideal pick?

 

[strmrdr]

Date: 4/28/2005 3:17:36 PM
Author: Regular Guy
So...if trying to keep it simple...


I will confess having some of the same concerns Nerdbot recently confessed, at picking well...based on my eyes, anyway. So, if trying to keep it simple, to what extent is there agreement that, having sorted with the HCA, then using a tool such as the idealscope, perhaps coupled with an H&A viewer (used only if only the expectation of H&A is present?) would be sufficient to make what an expert could be expected to regard an an ideal pick?

A loupe would be mandatory but beyond that.

If I could only have one tool to use with the hca it would be an ideal-scope.
The combo will further filter the poor performers out over just using the hca.
Then id add in the H&A viewer to sort by optical symmetry.
That leaves you with the best of the best.
Now to pick from them the sarin report, b-scope, isee2, photos, and very much most of all an experienced vendor that understands super-ideal diamonds backed up by a great appraiser come into play.

 

[aljdewey]

I''ve no idea why, but you guys really make this much harder than it has to be.

1. Use the HCA to reject stones that are unlikely to hold promise.
2. When you''re down to a few, use an Idealscope to make sure they don''t leak light.
3. Once you''ve done those, YOU CANNOT PICK INCORRECTLY. Choose whichever stone appeals to your eye the most.

 

[Dancing Fire]

i would like to see the sarin report first,if the stone has a "wide variance" i would pass because that tells me the stone is not very well crafted.of course i''m talking about a stone with a hca near 1.0 and a nice I-scope pic.

 

[Garry H (Cut Nut)]

Can i turn this around slightly?
If buying sight unseen:

If you have a nice ideal-scope image you have a nice stone.
If you have a nice HCA , then request an ideal-scope image, or ask for an honest opinion and let the appraiser be the judge.

A Sarin report is not of great value if you have the other info - but can help with girdle thickness - but the report info is better..

A Gem Adviser file wins (paper sizzors and rock).
A Sarin or Helium, 3D report can be translated by DiamCalc to a free downloadable software Gem Adviser

You can see ideal-scope, do light return and contrast - and soon a whole heap more with the next release - and check the girdle thicness all around, pick up under girdle naturals etc etc. Cant wait till it also shows the inclusions.

 

[Dancing Fire]

Garry
sight seen or sight unseen,i wouldn''t mind getting all the information that i can about the stone.