Spread Question?

[lmurden]

Can someone explain to me what spread means; what it means when someone says their 3/4 carat diamond has a spread closer to a 1 carat diamond; and how you can figure what the a diamond spread is? Thanks

 

[MelanieC]

Hi there,

The spread of a well cut 1ct diamond is around 6.5mm. If you visit a mall, you will see that the average mall 1ct is approximately 6.2mm with some even as low as 6.00 or more!!

A well cut .85 - .95 can be as large in spread (how much of the diamond you see when viewing from the top (table) as some of the badly cut mall ones.

A well cut .80 should be approx. 6.00mm and a .95 should be approx. 6.4mm.

Does this make sense? Hopefully I explained it good enough!

 

[cflutist]

As MelanieC said, the diameter of a well cut 1.0 ct diamond is 6.5mm.
The diameter of a well cut .75 ct diamond is 5.8mm. If it has a 1.0 ct spread, that means it faces up as if it were a well cut 1.0 ct stone even though it weighs only .75 ct. This means that the diameter of the spread .75 ct stone is 6.5mm when it should be 5.8mm if it were cut well.

Since diamonds are sold by weight, that means something's gotta give ... which means it probably has a shallow pavillion. When the pavillion is shallower than 38 or 39 percent, the girdle reflection becomes an unattractive ring lying right under the table (aka "fisheye") and the stone will be dull and flat looking.

 

[websailor]

Enough of the techie talk! Both the above posts are correct.

In layman's terms, both the 1.0ct and the .75ct stones have the same size face, but the .75ct stone does not have the "depth" it should have....it's been flattened out.

Sort of like taking a penny, putting it on the railroad tracks, and letting the locomotive make it the size of a quarter.

It just won't look right, even though it is still a penny, and looks kinda like a quarter, but not even that looks right....

 

[noobie]

If you take the cube root of the carat weight and multiply it by 6.5 it will give you in mm what a well cut diamond will approximately spread, give or take.

 

[lmurden]

Thanks for the all the informative answers, but how do you figure out the what the spread is? Do you just measure the diamond face up with a ruler? Thanks again.

 

[MelanieC]

The easiest way if your buying a certed diamond is to look on the cert for the measurements.

Example of my 1.085 6.55-6.59 x4.08mm

If it's not certified, I guess measuring with a mm ruler is the only way. Any experts know how you would tell at a jeweler where they are not selling a certified diamond?

 

[chialea]

That would be reaaaally hard to measure with a ruler. I think you're going to want a pair of precision calipers, which I would assume the dealer would have if they're selling uncerted stones. (Or at least I would they would!)

 

[lmurden]

I will be getting GIA or AGS stone and they will have the measurements on the certificate but once you see the measurements then what does it mean?

For example, MelanieC measurements are 6.55-6.59 x4.08mm that equals to 0.1632 what does that mean? How do you translate that to 5.8mm or 6.2mm? I hope this isn't a ridiculous question?

 

[Shay37]

Imurden, that 6.55-6.59 is the diameter measured across the top of the stone. One direction it measures 6.55, the other direction it measures 6.59. That equates to the 5.8 and 6.2 you just asked about. The 4.08mm measurement is the depth of the stone. You don't actually multiply the first two numbers by that even though there is an "x" there. It's like saying two by four and writing it 2 x 4. Hope this helps.

Shay

 

[glitterata]

The spread is the diameter. When you look down at a diamond from the top, you see a circle. The spread is how wide that circle is.

When you're measuring a diamond, "6.55-6.59 x4.08mm" doesn't mean "subtract 6.59 from 6.55 and multiply the result by 4.08." It means, "The diamond is 6.59 mm wide at its widest point and 6.55 mm at its narrowest. The measurement from top to bottom is 4.08 mm." So the "spread" of that diamond would be the average of 6.55 and 6.59, or about 6.57 mm.

 

[lmurden]

I get it now! Thanks

 

[researcher]

I know you all are round experts, but I just wanted to add that the average diameter of a 1 ct princess is closer to 5.6mm

 

[glitterata]

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On 7/29/2004 7:42:14 PM researcher wrote:

I know you all are round experts, but I just wanted to add that the average diameter of a 1 ct princess is closer to 5.6mm

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Except that a square doesn't have a diameter. If the average length of the side of a 1 ct square princess is 5.6 mm, the average diagonal is 7.9 mm and the average area is 31.4 square mm. The average area of a well cut 1 ct round is 33.2 sq mm. So a round might look a bit bigger than a princess of the same weight, but not as much bigger as the difference between 5.6 mm and 6.5 mm would suggest.

(With fond memories of my high school geometry teacher, and great relief at having been allowed to use a calculator to figure all that out, not a slide rule...)

 

[researcher]

Excuse me for not using the proper verbage. What I meant by "average diameter" is the average of the length and the width. I've done more math in my life than most people (currently finishing up my Ph.D. in structural equation modeling) so I do know the proper language, but was trying to not confuse people--guess it backfired!

 

[glitterata]

I apologize, researcher--I didn't mean to be snippy. I was just trying to add more info. It's so hard to get the tone across online!