Diameter Deviation - How Important?

[SeekingNiceIce]

Hi Everyone,
I''ve only been reading this forum for a short time, but it seems exceptionally useful and educational! I''m in the market for a very nice round brilliant stone for an engagement ring. I''m looking at E color, VVS2 clarity, 1ct+ (~1.00 to 1.20 range), looking for a very high quality stone. I found one (GIA certified) described as follows:

ROUND BRILLIANT
6.49 - 6.56 x 4.02 mm
1.05 carat
Depth: 61.6%
Table: 57%
Girdle: MEDIUM, FACETED
Culet: NONE
Polish: EXCELLENT
Symmetry: EXCELLENT
Clarity: VVS2 (2 small pinpoints in table...I couldn''t see them with a loupe)
Color: E
Fluorescence: NONE

I''m thinking this is a great stone, but, I don''t know the details like crown angle (or depth) or pavillion angle (or depth). It sure sparkled though!

Most stones I see certs on seem to have less of a diameter deviation than this stone though. Should I be concerned? I can get this stone for $8200...is it a good price due to some defect I''m not picking up on?

Thanks in advance for the advice!

 

[pricescope]

1% variation in diameter is rather average for round stones.

 

[niceice]

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On 5/27/2004 3:22:14 AM SeekingNiceIce wrote:

]*** SeekingNiceIce ***
----------------

We're right here

Couldn't resist

 

[SeekingNiceIce]

Oh, there you two are!

Nice to meet you.

I guess the name I chose was not so unique after all (and I thought I was being clever!).

 

[niceice]

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On 5/27/2004 2:48:30 PM SeekingNiceIce wrote:

Oh, there you two are!

Nice to meet you.

I guess the name I chose was not so unique after all (and I thought I was being clever!).----------------

We think it's clever

Can you get the dealer who showed you the diamond to obtain the crown angle and pavilion angle measurements for you?

 

[SeekingNiceIce]

Hi NiceIce,

Well, I went back and asked him for the crown and pavilion angles, but he didn't have them. He said he'd have to send it to AGS and that it's expensive to do that. Or I could take it to a local gemologist, but I'd have to buy it to do that. He also said it's not really necessary to have that information because the GIA wouldn't have rated it with Excellent Symmetry if the angles were far off. I'd feel better knowing...and I'm not so sure what I think of his answer. I guess since it's not on the GIA certificate, it's not that easy to come by...or is that wrong?

 

[Magnum]

"He also said it's not really necessary to have that information because the GIA wouldn't have rated it with Excellent Symmetry if the angles were far off."

Absolutely false!

GIA graded symmetry does not tell you any thing about the angles. GIA will tell you in the comments section if the crown angle is greater than 35.5 degrees or less than 30 degrees (I think those are the right cut offs, please correct me if I'm wrong), but that doesn't tell you very much, anyway, and has nothing to do with their symmetry grade. The reason NiceIce asked for the crown and pavilion angles is because the relationship between those two angles has a very large effect on the light performance of the diamond, and plays a big part in determining the quality of the cut. You can have an E VVS2 diamond that looks dull and dark, and an I SI1 that sparkles like crazy, and the reason is the cut, not the color/clarity/GIA symmetry. You definitely sound like your willing to pay for top color/clarity, so i don't see why you shouldn't demand to know that you're getting a top of the line cut stone as well. Saying all that, you've seen the stone, and you said it sparkles, so it could be a great cut. You just don't have enough info to confirm that. Personally I'd want more info on the cut to be sure that it is a great cut diamond, and didn't jsut look good because of all the bright lights in the jewelery store. Just my 2 cents.

If you want to learn more about what GIA symmetry really is, try these links:

Goodolggold symmetry

NiceIce symmetry

And here is a driect quote from the NiceIce link:

"Symmetry refers to the precision with which the facets of a diamond are aligned with each other and the consistency of facet shape and size per given section. The symmetry rating reflected on a diamond grading report is not an indication of the proportions of a diamond."

 

[zeytoun]

Here's a rather odd suggestion:

you could find a friend with a crown angle viewer (which only take about 5 minutes to figure out how to use), take it with you to the jeweler, and calculate the angles yourself. I know that's probably not very helpful, but I'm the guy who gives "out there" suggestions which every now and then work.

 

[SeekingNiceIce]

Magnum - thanks for the clarification on symmetry. What the jeweler told me didn't really jive with what I've been learning, but he was insistent. I guess not every truly knows what they're talking about...or they're trying to fool you so you'll buy. He should join Pricescope and learn more

Those links you provided were a great source of information, too! I personally want more info on the cut of this stone too, but am struggling on HOW to get it.

Zeytoun - thanks for that suggestion. I only wish I did have a friend with a crown angle viewer. I tried to look up information on one and couldn't even find anything on it on the web. Great idea though - I'm the kind of guy who would like to measure that myself, too. If they were inexpensive enough (which I doubt) and I could find one, I might even do that. It's strange that with such an important thing about a diamond as cut, they don't provide all the critical information so you can determine how good the cut it.

GIA should certainly add crown and pavilion angles to their certificates...

 

[Magnum]

"I personally want more info on the cut of this stone too, but am struggling on HOW to get it."

That's the $64k question. Since this vendor apparently is unable to provide you with adequate cut information (not all jewelers have sarin machines, and other state-of-the-art equipment), you can either find a vendor (either B&M or internet) that can provide the cut information that you want or if you really like the stone, you can ask the vendor to send it to an indepndent appraiser that has the experience to evaluate the stone, and the technology to give you the cut information you're looking for. I'd ask him to do that before you buy the stone, or get a detailed explanation of his return policy, so you can take the stone for appraisal after you buy it, and return it if it doesn't meet your expectations.

 

[Garry H (Cut Nut)]

Quiz question:

Why can a brilliant cut diamond, that measures exactly the same diameter in all directions, be actually badly out of round?

In this example it is possible for a diamond to have worse symmetry than a diamond with diameter deviation of more than 5% (e.g. 6.30mm x 6.60mm)

 

[Magnum]

A: If it bulged out on one side, and bulged in on the exact opposite side.

 

[Garry H (Cut Nut)]

Warm, very warm!

 

[zeytoun]

offcenter culet and/or table?

 

[Garry H (Cut Nut)]

Cold

 

[jadeleaves]

Erm.. there is a large crown angle variance??

don't shoot me, I am still learning!

 

[Magnum]

To expand on my first answer, if it did what I described numerous times, but to a lesser degree than one big bulge and recess. Basically you could have a wavy girdle in the horizontal and not in the vertical (thickness) that is usually talked about. As long as the crest of one wave of the girdle lined up with the trough of another wave on the opposite side of the diamond, the diameter would be the same all the way around, but the diamond wouldn't be a perfect circle. So, my revised answer is a wavy girdle in the horizontal plane.

 

[Garry H (Cut Nut)]

Hmmmm
I think you are getting cooler.
Want to try to draw it, just a rough sketch in paint or adobe etc will do Magnum

Sorry Jade leaves, your cold

The variation must be in the diameter, not in the verticle direction.

Actually we beleive this occurs in around 10-20% of all diamonds but because neither a Sarin scan nor a measuring device can detect it, it has gone unnoticed for more than a century!!!

My favorite saying "Common sense is not common"

Those who know about diamond rough - what are the common crystal habits? The one we want would be 2nd or third most common variant.

 

[valeria101]

Diameter variation

... well, you could have alternating concave and convex segments around the girdle ( basically a sinusoid, like drillend holes have, or whatever object with round section that was formed through a rotating mechanical motion, continuous or not). To know precisely what type of deviation is likely, I'd need to know what the stages of cutting that determine the girdle outline look like.

 

[valeria101]

SeekingNiceIce,

why not seek the diamonds of NiceIce? These guys have pretty high standards when it comes to cut quality (and everything else, I suspsect)

 

[Garry H (Cut Nut)]

http://www.antwerpdiamonds.be/diamonds-diamond4.htm
Here is a link with inmages

It is not such a hard shape to explain

(I practice linking but fail

)

 

[valeria101]

Thanks !

From what I remember, the fastest the rotation and the more "rounds" done, the worst such uneven carving can get (meaning the tollerance for axial movement gets down exponentially). The kind of device in the pic, doesn't seem to make thousands of rpm ! At least as far as a little model can tell, faceting the girdle first is the most precise method, bt also the most wasteful (probably nothing new, but interesting for someone new to the game

)

making links... Here's how the following one got made Diamond Carving

 

[Magnum]

"The variation must be in the diameter, not in the verticle direction."

Cut Nut,
That's what I was trying to say. If you reread my previous post, you'll see I was trying to specify a wave in the horizontal/diameter direction (NOT the vertical), basically a sine wave as valeria said. i'm still not sure if that's what you were exactly looking for, but that's what my aswer was.

"To expand on my first answer, if it did what I described numerous times, but to a lesser degree than one big bulge and recess. Basically you could have a wavy girdle in the horizontal and not in the vertical (thickness) that is usually talked about. As long as the crest of one wave of the girdle lined up with the trough of another wave on the opposite side of the diamond, the diameter would be the same all the way around, but the diamond wouldn't be a perfect circle. So, my revised answer is a wavy girdle in the horizontal plane.

 

[Garry H (Cut Nut)]

OK Mag, but there is a very simple shap that your complex description could be describing.
To win the fish what is it?
What shaped rough produces it?

It is as a direct result of the bruting process and the shape of a particular type of rough diamond that is fairly common.

And thanks AnA for the lesson - I see what i was doing wrong now

 

[fire&ice]

People buy diamonds all day long with no crown & pavillion angle. I doubt whether all these stones are dogs. Your eyes have seen the stone. Have you compared it with other stones of it's size. One's within "idealish" range of table, etc? If the stone speaks to you & you like the person you are dealing with, then it could be the one.

If you still have doubts, buy the stone & have it independently appraised w/ the caveat that you can return the stone for full refund within x amount of days. Your cake & you can eat it to.

From just the numbers you provided, the stone sounds nice. It happens; but, stones with this sort of care taken in cutting are usually not dogs. And, your eyes are the only # that matters in the end.

 

[Garry H (Cut Nut)]

I give up - here is the answer

Maccle or triangular shaped twinned rough will result in slight triangular deviations after bruting.

Octahedral rough typically has a squarish outline.

 

[Magnum]

Ineteresting. I was trying to do some research to figure it out

, but it's tough to find info on the net about diamond cutting in detail. I found out that the two most common types of rough were tetrahedron and dodecahedron shaped, but I didn't realize triangular shaped was the third most common. I looked at those too as options, but they were even sided polygons (when you look down on the girdle they are four side and ten sided, respectively), and it would have to be an odd sided polygon (like a triangle) in order for the diameter to be the same all the way around. I don't know if rough comes in any other shapes that have an odd number of sides, but if it does, that might also result in some out of round cuts with a diameter that appears to be round. Of course, the deviations probably wouldn't be as bad as triangular shaped rough, since there are only three sides, and the more sides you get, the closer it is to a circle, anyway. Thanks for the challenge. I was getting close, but i just couldn't find out enough info on diamond rough and bruting, in particular.

 

[valeria101]

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On 5/30/2004 10:33:06 PM Garry H (Cut Nut) wrote:

I give up - here is the answer

Maccle or triangular shaped twinned rough will result in slight triangular deviations after bruting.

Octahedral rough typically has a squarish outline.----------------

This is something else! Didn't get it previously...

However, regardless of what the shape the rough is, the way it is rounded by a rotating tool can also produce "off round" shapes with the same "diameter" all over. This probably sounds too bad to be true in practice

What was I thinking?

 

[Garry H (Cut Nut)]

This idea came from Sergey and his partner in scanners. It is amazing that you can scan a diamond on any device (other than helium) and it can not detect such a simple and nasty deviation.

 

[SeekingNiceIce]

Thanks Fire&Ice for your advice. You're probably right that this stone IS a nice one based on everything I know. I'm just the sort that does sweat the small stuff sometimes...especially when there is a lot of $ involved. I may just look into the details of the return policy, buy it and have it analyzed, then return it if it falls short.

Thanks Gary and the rest for the education on the potential for out-of-round stones, too! I had no idea these existed out there...

Best regards to all!