Jan 292012
 

Next up the diamond cutter is getting ready to polish the first facet on the diamond… the table facet.  Polishing is done on a charged diamond wheel, the diamond is held in a dop, placed in a tang and carefully polished.

With the diamond secured polishing on the wheel can begin.

Finally, after weeks of analyzing the diamond, polishing windows and laser cutting… the cutter can finally get the start the first facet.  The table facet starts to come to life, still tough to tell what the final shape will be though isn’t it???   😉

A diamond is made out of pure carbon (the same material as in your pencil – the only difference is the bonding).  Unlike a led pencil which is very soft, only a diamond can cut a diamond.  The cutting/polishing wheel is charged with diamond dust, after polishing you can see a lot of black ‘stuff’ next to the polished section.  That ‘stuff’ is the carbon that was removed during the polishing process.

Jan 262012
 

The next step in the process for this diamond is to have it laser cut.  The shape of the rough and any inclusions determine where the diamond will be cut.

In preparation for the laser cut a few things needed to be done.  The rough diamond had an inclusion right below the surface, so it was fairly easy to remove.  The diamond was polished down to get rid of the inclusion, reduce some stress on the stone and provide a better view into the heart of the diamond.

Looking through the frosted rough diamond can only tell you so much about any inclusions inside.  Imagine looking in your bathroom mirror after you get out of the shower, it is all steamed up and you can’t see.  With a facet on the diamond the cutter will have a clear window that lets him see deep inside.

A black line is drawn on the diamond with a very fine maker to indicate where it should be cut.  You can see the black line on the diamond in the photo below.  With the cutting line marked the diamond was cut in half with a laser saw.

The small piece on the left side is 4.26ct and larger piece comes in at 18.17ct (some weight was lost when polishing the window).

With the work performed so far we are down to 18.17ct so we have lost 5.69ct from the large piece of rough.  A lot more of the precious diamond will be lost at it is transformed into a blazing ball of light…  more photos to come…

Jan 192012
 

I recently did a couple of postings about diamond cut and posted a diamond recut chart that can be used to give an estimate of how much weight would be lost to improve diamond cut.

Lets take a look at a real example on a stone.  When purchased the stone was nice, but a little deep.

Prior to being recut it was 1.15ct so there was room to improve it without going below 1.00ct, which wold be a bad financial move.

Specs Before Recut

Carat: 1.15ct
Measurements: 6.59 – 6.65 x 4.26
Pavilon Depth: 64.4%
Table: 57%
Girdle: Medium – Slightly Thick, polished
Culet: None
Polish: Very Good
Symmetry: Very Good
Cut Grade: Very Good

The cut grade on the above stone would have very good, excellent would not be possible because of the depth being 64.4%.

Off to the cutter it went for a little tune-up.

Specs After Recut

Carat: 1.10ct
Measurements: 6.59 – 6.64 x 4.12
Pavilion Depth: 62.2%
Table: 55%
Girdle: Thin to Medium, Faceted
Culet: Very Small
Polish: Excellent
Symmetry: Very Good
Cut Grade: Excellent

The angle of the pavilion would need to be increased in order to give the stone less depth, resulting in a more impressive stone.  When reducing depth you do not change the diameter of the diamond much.  On this diamond there was no change in the face up size.

The final weight loss was about 4.34%, according to the diamond recut chart we should have lost about 4% going from a depth of 64.4% down to 62.2% so the chart was right on.

Jan 152012
 

Since the GIA released their cut grade system in 2006 people have become obsessed with diamond cut.  Of course there are still plenty of diamonds that were cut before grades were established.

There can be some very interesting cut diamonds out there.  People can sell their diamonds @ http://www.diamonds2cash.com, when we buy diamonds that are badly cut by today’s standards we have to recut them to make them salable.

The following chart can be used to provide a rough estimate of the weight loss required to ‘fix’ a diamond’s cut.   Recutting the diamond is not always so simple, such as if there are large naturals or inclusions but for a quick calculation on the fly, the following data can be used to estimate the final weight of a modern round brilliant diamond.

Diamond Recut Chart

Depth Percentage Deduction Table Percentage Deduction
50.0 – 51.9 22%  43.0 – 45.9  8%
52.0 – 53.9 20%  46.0 – 48.9  6%
54.0 – 54.9  16%  49.0 – 52.9  4%
55.0 – 56.9 12%  53.0 – 53.9  3%
 57.0 – 57.9  8% 54.0 – 54.9 2%
 58.0 – 58.9  6%  55.0 – 56.0 0%
 59.0 – 59.9  4%  56.1 – 58.0  2%
60.0 – 60.9  2%  58.1 – 60.0  3%
 61.0 – 62.0  0%  60.1 – 63.0  4%
 62.1 – 63.0  2%  63.1 – 65.0 6%
 63.1 – 64.0 4%  65.1 – 67.0 8%
64.1 – 65.0 6%  67.1 – 69.0  10%
65.1 – 66.0  8%  69.1 – 73.0  12%
66.1 – 67.0 12%
 67.1 – 68.0 16%
 68.1 – 69.0 18%
69.1 – 70.0  20%

 

Diamonds with a table between 52% – 62% have the potential to fall within GIA’s top cut grade (excellent) but it depends on a number of factors.  Diamonds with a table size outside that range would need to be recut for sure in order to obtain an excellent cut grade.

 

Jan 112012
 

How about a 23.86ct diamond?

Most people consider a 1ct diamond to be big, a target size for millions of diamond lovers around the world.  A 2ct diamond, getting bigger… a 3ct diamond or larger and eyes start popping.



Not what you are used to seeing?  That is a rough diamond, it is currently being cut (January 2012) and we are going to be following this diamond as it is worked on the diamond wheel and brought to life.  Will it end up being round, princess cut, oval???  Currently only the cutter knows how this one is going to end up.

23.86ct Diamond In The Rough

Stay tuned for more posts on this little guy and hopefully we can learn a thing or two from the diamond cutter about diamond cutting along the way.

Jan 112012
 
GIA Master Stones

Master Stone Set

I am one of the diamond buyers over at diamonds2cash.com, a customer who is considering selling a diamond has an appraisal that states:

Cut: Round Brilliant
Estimated weight by formula: 1.10 carats
Clarity: VS-2
Color: “L” as set
Symmetry: Good
Polish: Good

The seller was curious about what “L” as set means.

Color Grading

When grading the color of a diamond, ideally they are placed table down next to a master stone and the color is compared to the diamond of known color.  A grader will have a set of master stones in a number of colors and  check the stone being graded to the masters until they find the closest match.

That is the ideal situation…  often appraisals must be done when the diamond is set in a ring or another piece of jewelry.  The color and setting style can have a major impact on the appearance of color.

When set in jewelry the diamond may appear to have less color than it actually does, placing a yellow “M” color diamond into a platinum setting may give it the appearance of it being K or L in color (or even higher!).

Only if the diamond was removed from the setting could the actual color be determined.  It is a bit of guess work when grading color of a set diamond so an appraisal will indicate that the diamond was graded set as a warning that the information may not be 100% accurate.

Major diamond grading labs such as the GIA will not grade diamonds unless they are loose, simply because they can not be 100% certain about the diamonds 4C’s when mounted.

Jan 012012
 

I personally know a few other G.G.’s which I have met while working in the industry, as well as a few I know from attending the GIA.  Some of them hold very interesting positions and I hope to entice them to do some guest posts for the site.

So far I’ve got a few G.G.’s that will be submitting guest articles, but if you are a gemologist and would like to write a guest article please get in touch with me.