Why does a round diamond have different length and width?

[helios_haze]

I may be weak at geometry but ...

How can a round have different length and width?

E.g. 7.97 - 7.93 - 4.85 mm (L - W - D)

Is this badly cut?

I tried searching for a diamond with the same length and width but came up with nothing

 

[honey22]

Not at all! The stone is fine and well within ''round''. We are talking less than 10ths of a mm here, there is nothing to be worried about at all.

Get a ruler and try to imagine what a 10th of a mm looks like and you will see that it''s not a problem

 

[helios_haze]

Point taken!

But, don't they use machines to cut these? Isn't 1/25 th of a mm sizeable in this day and age of microns and nanotubes??

 

[John P]

Date: 8/4/2008 11:57:36 PM
Author: helios_haze

Point taken!

But, don''t they use machines to cut these? Isn''t 1/25 th of a mm sizeable in this day and age of microns and nanotubes??

When you''re working with many substances, sure. But diamond is unlike any other substance, which is why it is so highly valued. As you might already know, diamond is not actually "cut" by anything other than another diamond: Rotary saws and wheels are coated with diamond dust to accomplish this...lasers can vaporize...but nothing but diamond can cut/polish another diamond.

On the Moh''s hardness scale iron is 4 to 5. Quartz is 7 and even hardened steel is only 7 to 8. Diamond is the hardest substance in the known universe. at 10 on the Moh''s hardness scale it''s actually many times harder than corundum, which comes in at 9.

Click here for a visual representation: http://www.allaboutgemstones.com/images/mohs_hardness_scale.jpg

 

[helios_haze]

Thanks John ... great information!

But, I still do not have a clear answer to my question. Why is a RB not a geometric round/why is the cut radius uneven? I infer from John's post that the hardness of diamond makes it very difficult to cut. However once the diamond-dusted saw MACHINES are rolling and cutting, why can't they hold steady.

Don't mean to be difficult - just curious

 

[John P]

Date: 8/5/2008 2:06:10 AM
Author: helios_haze
Thanks John ... great information!

But, I still do not have a clear answer to my question. Why is a RB not a geometric round/why is the cut radius uneven? I infer from John''s post that the hardness of diamond makes it very difficult to cut. However once the diamond-dusted saw MACHINES are rolling and cutting, why can''t they hold steady.

Don''t mean to be difficult - just curious

It''s not as simple as kicking a machine into action helios. I''ll try to explain before I mosey off to bed.

Like wood, diamonds have grain. You must work with the grain in mind and this starts far before any action is taken, back when the designer, sawyer and polisher all examine and plan the rough crystal. Once the designer/planner understands the shapes he wants to yield it must be decided (for sawables) where to saw. After the rough is sawn (which can take a long time) the process of bruting/girdling the sawed octahedron into a roughly round shape takes place (for rounds). Once the shape is made round the long process of blocking/cross-working and brillianteering begins.

Some simplified diagrams follow (acknowledgment to the PS H&A tutorial).

An octahedron, which in the case below will yield two halves of equal size, is sawed along the sawing grain - often it is not sawed directly in the center, in order to yield two different sized polished diamonds, or to plan wisely around inclusions.

Below are some photos of natural rough pieces:

 

[John P]

Here the designer plans the yield (see the computer screen), and considers the lie of inclusions, coloration, etc.

 

[John P]

Here a piece of rough octahedron is being sawed. Diamond dust will constantly be applied to these saws, which must be monitored through the process.

 

[John P]

A row of saws.

 

[John P]

Once sawn, a piece that will become a round must be girdled. This is done by turning the diamond at high speed against a wheel impregnated with diamond dust.

Less than 200 years ago “bruting” (girdling) was a long, agonizing process. It involved attaching two diamonds to sticks and the bruter (called a diamond cutter in those days) would wear leather gloves and strike or rub them against each other to eventually shape the diamond’s outline. It could take days or weeks and “round” was never a guarantee. Most cutters’ hands gave out eventually.

Here is a modern girdling machine running.

 

[John P]

You can see the sawn rough slowly being made circular.

 

[John P]

Once roughly round, with the table in place (the sawn flat area becomes the table) the process of blocking begins.

Here are diagrams of this - again, courtesy of PS H&A tutorial. You can see top and side illustrations of the crown as it is blocked in four around the table facet.

The crown finished in eight cut.

Bottom and side views of the pavilion as it is blocked in four.

And in eight cut.

Illustrations of the whole blocking/cross-working and brillianteering process.

 

[John P]

You asked about machine-cutting.

Some diamonds are able to be blocked by machine, depending on their grain, and if you don’t mind inconsistent results diamonds in common sizes can be finished by machine, but machines still do not have the human craftsman’s ability to feel the crystal and negotiate graining and inclusions in real time with intuition. Machines are able to cut melee to great accuracy, but human polishers at the top of their game still “feel” the crystal better and more accurately in common sizes than machines.

Here is a blocking machine at work.

 

[John P]

A diamond’s crown shown in eight cut.

 

[John P]

The finest precision-cutting is still done by hand. Every time that crystal touches the wheel some of it is forever polished-away. Every facet’s placement must be planned precisely, working around and across the diamond, “feeling” the grain, understanding and coping with inclusions, correcting as necessary and adjusting the entire map of the faceting when corrections occur, in real time.

 

[John P]

After every kiss of the wheel the diamond is checked, adjusted, reapplied, checked, adjusted, repeated... For great polishers it’s flow, pacing and concentration not unlike like a long distance runner; moving, breathing, feeling the slope, checking pulse and making no missteps.

 

[arjunajane]

Awesome pics and info as always John, thanks for sharing!

 

[Lorelei]

Date: 8/5/2008 3:29:31 AM
Author: arjunajane
Awesome pics and info as always John, thanks for sharing!

Indeed, absolutely fascinating, many thanks Sir John for sharing that with us!!

 

[John P]

And finally… This isn't a usual specimen, but I thought it would be a nice finish to these pictures with a modest little 15-carat treat.

You can be sure a lot of planning and devotion went into this pretty little firecracker, but at the end of the day it isn't perfectly round. However I'm betting the lady wearing it isn't losing sleep over that fraction of a millimeter.

 

[John P]

Date: 8/5/2008 3:31:46 AM
Author: Lorelei

Date: 8/5/2008 3:29:31 AM
Author: arjunajane
Awesome pics and info as always John, thanks for sharing!

Indeed, absolutely fascinating, many thanks Sir John for sharing that with us!!

My pleasure, m''ladies. I am in awe of the masters of these crafts; sorting, grading, planning, polishing...all of it.

And I appreciate you saying something.

 

[Lorelei]

Date: 8/5/2008 3:39:56 AM
Author: John Pollard

Date: 8/5/2008 3:31:46 AM
Author: Lorelei

Date: 8/5/2008 3:29:31 AM
Author: arjunajane
Awesome pics and info as always John, thanks for sharing!

Indeed, absolutely fascinating, many thanks Sir John for sharing that with us!!

My pleasure, m'ladies. I am in awe of the masters of these crafts; sorting, grading, planning, polishing...all of it.

And I appreciate you saying something.

Most welcome Sir, it is wonderful for us to be able to see these pics and get a peek into the world where the magic happens!!

15 CARATS???? MARA!!!!!

 

[Paul-Antwerp]

It may not have been clear in John''s posts, but the main reason for the stones not being perfectly round is that the growth of the diamond crystal (the grain) created four areas on the girdle with strong directional strength and four areas with weak directional strength.

Live long,

 

[Lorelei]

Date: 8/5/2008 4:41:54 AM
Author: Paul-Antwerp
It may not have been clear in John''s posts, but the main reason for the stones not being perfectly round is that the growth of the diamond crystal (the grain) created four areas on the girdle with strong directional strength and four areas with weak directional strength.

Live long,

Thanks Paul, this is all great info!

 

[Deelight]

Date: 8/5/2008 3:31:51 AM
Author: John Pollard
And finally… This isn''t a usual specimen, but I thought it would be a nice finish to these pictures with a modest little 15-carat treat.


You can be sure a lot of planning and devotion went into this pretty little firecracker, but at the end of the day it isn''t perfectly round. However I''m betting the lady wearing it isn''t losing sleep over that fraction of a millimeter.

OMG that is beautiful

, thanks for the piccies John very informative.

 

[Garry H (Cut Nut)]

Great demo John!!!!!


Each crystal face has a different hardness towards a point than it does toward an edge. There are octaedral triangular faces with 3 hard and 3 softer, cube faces with 4 hard and 4 softer and dodecahedral faces with the 2 softest and 2 hard.

If the rough has a table on the cube you get slightly squarish diamonds from bruting
if it is a doddeca then there is a little bit of ovalness
if it is an octahedra then it tends to measure perfectly round but the radius varies in 3 directions

wanna guess why?

 

[ksinger]

I just love PS!

Thanks John!

 

[helios_haze]

WOW!!! One for the ages!!!

Thanks John, Paul, and Garry. You guys rock (And I mean 15ct style)

 

[Lorelei]

Date: 8/5/2008 10:03:41 AM
Author: helios_haze
WOW!!! One for the ages!!!

Thanks John, Paul, and Gary. You guys rock (And I mean 15ct style)

Definitely, FABULOUS thread!!!!

 

[Ellen]

Date: 8/5/2008 10:05:29 AM
Author: Lorelei

Date: 8/5/2008 10:03:41 AM
Author: helios_haze
WOW!!! One for the ages!!!

Thanks John, Paul, and Gary. You guys rock (And I mean 15ct style)

Definitely, FABULOUS thread!!!!

Ditto. Great work John.

 

[HariSeldon]

Date: 8/5/2008 1:49:20 AM
Author: John Pollard

Date: 8/4/2008 11:57:36 PM
Author: helios_haze

Point taken!

But, don''t they use machines to cut these? Isn''t 1/25 th of a mm sizeable in this day and age of microns and nanotubes??

When you''re working with many substances, sure. But diamond is unlike any other substance, which is why it is so highly valued. As you might already know, diamond is not actually ''cut'' by anything other than another diamond: Rotary saws and wheels are coated with diamond dust to accomplish this...lasers can vaporize...but nothing but diamond can cut/polish another diamond.

On the Moh''s hardness scale iron is 4 to 5. Quartz is 7 and even hardened steel is only 7 to 8. Diamond is the hardest substance in the known universe. at 10 on the Moh''s hardness scale it''s actually many times harder than corundum, which comes in at 9.

Click here for a visual representation: http://www.allaboutgemstones.com/images/mohs_hardness_scale.jpg

Just FYI , a diamond isn''t the hardest substance in the universe anymore. Aggregated carbon nanorods have been synthesized that are harder and more dense than diamonds.