The Graduate Gemologist

I often like to window shop at jewelry stores, just because I like the bling.  I don’t actually like going into jewelry stores, I feel very out of place and hate how they hover over you.  Or maybe I just look like trouble, so they stick close 😉

Anyway, today I was walking in Central (Hong Kong) and spotted this little guy.  A 12.01ct D Internally Flawless diamond, darn no price listed.   I snapped this photo with my phone and sent it to gemologist friend and went on with my day.

Then I thought I am going to go back there and ask how much it is.  When I was leaving Central I stopped into the shop, they were very friendly and answered all my questions about the diamond.  I got the full specs, including the GIA report details (report #15782646).

Here are the specs:

Carat: 12.01ct
Measurements: 14.67 – 14.71 x 9.15
Color: D
Clarity: Internally Flawless (there is one grade higher than this, which is flawless)
Cut: Excellent
Symmetry: Excellent
Polish: Excellent

Their asking price is 30,208,700 Hong Kong Dollars, which is about 3.8 million USD.  If you are interested the shop is Chow Sang Sang @ 37 Queen’s Road, Central, Hong Kong.

Obviously an incredible stone, but I was surprised the GIA report is from 2008.  If I was dropping 3.8 million on a diamond I would want a current report.  Odds are very good this diamond has been ‘previously enjoyed’ and if it has suffered any damage at all since it was graded in 2008 then it would no longer hold the IF grade.

So if you stop in to buy it, make sure the purchase is contingent on the report being updated by the GIA and that it still holds the IF grade.

Diamcor Mining is a small publicly traded company (DMI.V) that is based out of Canada and is actively mining in South Africa.  I had the pleasure of taking taking my GIA G.G. program with one of their high level staff.

I follow the companies press releases just to see what they are doing.  For years they were processing diamond tailings from and old mine and seemed to ‘get by’ but not much else.   They started working a new diamond mine earlier this year and it looks to be paying off!  They recently sold this 91.72ct rough diamond that they pulled up for $817,920.00 (US).

I don’t think they released any color/clarity information on the stone, guess that is up to the buyer to estimate but it certainly is an excellent octahedron example.  91ct… oh to dream.  Nice job guys!  If their mine can pull a few of these guys out a year they will find their stock pricing heading up for sure.

Some time ago a diamond dealer was cleaning out his desk (it must have been VERY dirty).  He found an old wholesale price list for diamond.  He sent it over to me via fax, so I’m posting it here for those who might find it interesting. This price list is from before the current GIA diamond grading scale was used.

Looks like you could buy a 1.5ct diamond, D color, Flawless clarity for $730 per carat…  you will not get deals like that these days!

A quick post about calculating diamond depth in a round diamond.

If you have a diamonds measurements, you can calculate the total depth of the diamond.  The total depth is a quick guide to ensure the diamond is ‘OK’.

To calculate the depth you divide the depth by the average of the  the minimum & maximum diameter.  The weight of the diamond does not have any impact.  The formula is the same for a 0.25ct diamond or a 50.00ct diamond.  Lets do a couple:

Measurements: 6.20 – 6.30 x 4.10

Depth / Average Diamater * 100

4.10 / 6.25 * 100 = 65.6% total depth   <- This diamond is quite deep and will not score a very high cut grade.

 

Measurements: 6.72 x 6.75 x 4.07

4.07 / 6.735 * 100 = 60.4% total depth <- This diamond has the potential to be very attractive.

 

That’s it!  This is for round diamonds, other shapes use different formulas.

Way back in February we sent a 2.13ct diamond to the cutters.  The diamond did not perform as well as it could (it was ugly) so it needed an overhaul.

Our little experiment was to be cut by numbers, based on the AGS cut grade scale.  The AGS uses a number scale with the highest grade being 0.  The worse a diamond performs in any area, the higher numeric value it gets.  Lets look at the numbers now that we got the diamond back:

AGS Light Performance

	Brightness	Leakage	Contrast	Light Performance	Proportion
Before	2.19	0.46	1.50	4.0	3
After	0	0	0	0	0

The diamond now scores a 0 in all of the above categories.  The diamond is now considered to have the best possible light return and sparkle it can.  The result is a diamond with excellent symmetry.  Here are some photos of the diamond as simulated in the computer.

The green areas in the left photo show where light is leaking out of the diamond. The more light that leaks out, the less that is returned to the viewer of the diamond. A diamond that leaks light does not have much sparkle.

Actual photos of the before and after as viewed in the AGS viewing tool.

On the left is the before view, you can see lots of green areas where light is leaking out. There is no symmetry in the diamond and the large black culet in the middle.  The right we have no culet and excellent symmetry. The diamond now scores and excellent cut grade (AGS 0) and is a real show stopper in real life.

Of course the downside of all this ‘improvement’ is we no longer have a 2ct+ diamond.  The final diamond weight is 1.87ct.   Some people would rather have a large diamond that does not perform as well as a smaller diamond.  That trend is changing though, most consumers now want diamonds that are excellent or ideal cut so this diamond should find a new home much easier now that is rates AGS 000 vs. being larger but a bit out of shape.

Would you prefer a larger 2ct+ diamond that is a bit out of shape, or a 1.87ct diamond that is a fireball of light?

I came across this 1.01ct diamond, bought it with plans to recut… but sold it for education purposes.

Most round diamonds cut these days fall within a certain range.  For example a total depth would normally be in the 58% – 64%.  These I would consider ‘normal’.  Sometimes the way a rough diamond is found a cutter may get creative and do something with a deeper cut to retain weight.

If a diamond is too far outside of this normal range it is going to need a recut, that is when I use the diamond recut chart to estimate what it will take to bring the diamond into acceptable portions and make it salable.

I could not believe my eyes when this one came in:

Wegiht: 1.01ct
Measurements: 5.8 – 5.9 x 4.44
Table: 56%
Total Depth: 75.2%

Right away I can see something is off with this diamond.  A 1ct diamond should have a width of about 6.5mm, this one is only 5.8mm so I know the depth is going to be very wacky.  It might have a very thick girdle, steep crown angle or steep pavilion angle (or maybe all three!).

If you calculate the diamond depth, you get 75.2%.  This is mind blowing to a diamond guy like me.  A true first!  No problem, just use the diamond recut chart to get an estimate of the weight after recutting to find out what you will end up with when the problems are fixed.

Wait just a minute…  this diamond is so far off the norms the recut chart does not even go that high.  The recut chart maxes out at a depth of 70% in which case you will loose about 20% of the diamond.

So what happened, did this little guy get recut?  Nope, the proportions were so wacky a diamond educator actually bought the diamond as it is – as an example of how bad a diamond can be cut!  It’s life was saved and will be used as a demonstration tool for years.

Way back in 1996 The American Gem Society Laboratories released their cut grade system.  The scale runs 0 to 10, with 0 being the best.  It was not until 2006 that the GIA released their cut grade scale, no surprise they are different.  The GIA uses words to describe their cut grades from Excellent to Poor.

To support their cut grade the AGS released the ASET which is a tool used to assess a diamond’s interaction with light.  The more light a diamond can return to the viewer’s eyes, the more impressive the diamond appears.

The tool is fairly easy to use and the results easy to understand, even to the untrained diamond shopper.

Essentially you want a diamond to have as much red as possible.  Light pink, green and black areas all represent light leaking out of the diamond.  When the light leaks out the viewer of the diamond does not see the sparkle or fire that would be shown if the diamond were well cut.

The diamond on the right does not look very healthy.  The symmetry is just not happening and it shows a lot of light leaking out all over the place.

While the diamonds visual appeal was not that bad (OK it was bad), it would not rank as an AGS 0.

Lets cut by numbers, we have sent this diamond out for recutting and it should be back in a few weeks.  I’ll do another posting when it comes back with the ASET photo and we can see the difference which will be amazing.

For those curious about the black stuff in the image, the dot in the very middle is a culet.  It is slightly large and most modern well cut diamonds do not have them or if they do they are very small.  The other black stuff down at the 6’oclock to 8’oclock area are inclusions.

* UPDATE * This diamond is back from the cutter, you can view the new diamond online and see how it turned out.