Oct 252013
91ct rough diamond

91ct rough diamond

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.


Sep 282013

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!

Antique Diamonds Prices

Antique wholesale diamond prices, click to enlarge.

Aug 252013

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.

Jul 272013

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.

Simulated Diamond View

Computer image of the diamond symmetry, before and after.

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.

Here is the side by side photo view of the actual diamond before & after.

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?

May 162013

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%


1.01ct diamond with 75.2% depth

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.

Feb 282013

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.

2.13ct Diamond

Our 2.13ct diamond before cutting

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.

Jul 292012

I posted a comment a few months back about diamond prices dropping, based on the official RAP price list.  We are seeing that prices are continuing to drop, which is bad news for diamond sellers.  The amounts of the drop that we are seeing is not massive like you might see on the stock market but a few % drop here and there do add up in the diamond trade.

A diamond that a few weeks ago may have traded for $5,000 might now be $4,700 today.  In times like this a lot of dealers just keep their inventory close to them, refusing to sell due to the loss they will incur if they do sell.  You see this type of thing int he stock market also, where sellers who own a stock fall in love with it and never sell – as they ride the price drops all the way to the bottom.

May 252012

Synthetic (man made/fake) diamonds produced by CVD (Chemical Vapor Deposition) have been around for a while.  There are companies making them and selling the finished diamonds on the market but the demand for them is quite small.

When our diamond buyers are making a purchase there are a number of diamond type(s) that we do not purchase.  Among the items we do not purchase are treated diamonds.  Synthetic diamonds are also something we would have no interest in purchasing.

All synthetic diamonds must legally be sold with full disclosure, stating that they are not natural.  However, when there is money to be made the crooks come out of the woodwork.

A batch of hundreds of CVD diamonds recently showed up at the IGI (International Gemological Institute) in both Antwerp and Mumbai for certification as natural diamond.  The IGI caught that the diamonds were not natural, however it is raising concern that a larger volume of these fake diamonds may have already entered the market.

A polished diamond dealer who sent the diamonds for certification claimed he bought the diamonds as natural from another dealer.

The IGI issued an alert which has been sent to dealers and diamond labs worldwide in attempt to keep the industry informed.

Debeers has also alerted their customers (sightholders) that it is aware of three recent instances of undisclosed CVD diamonds being sent to grading labs as well.  Debeers (Diamond Trading Company) has also issued a statement.

Synthetic diamonds entering the market without disclosure is certainly bad for the industry as a whole.

May 062012

If you deal with old jewelry, you know all too well about prying small stones from jewelry.  When getting a batch of old gold or platinum ready for refining it is best to remove the old stones.

Often the result is broken or damaged stones.  Not only does the process take a LONG time to sit there and file out old stones any damage damage hurts the recovered stone value.

We recently sent a batch of old rings to a refiner who does a chemical melt, the metal is put into a beaker and is broken down.  The stones fall to the bottom of the beaker, without damage.

We tried it with a service located outside the USA, but we have found one such company located in St. Paul, MN.

No actual experience with this company, but certainly take a look at Stebgo Metals if the idea of no longer doing removal of stones by hand is appealing to you.

Apr 152012

Back in February I did a posting on a diamond that had a fair cut grade, it was not a very attractive diamond.  Of course we sent it off to the diamond cutter to bring it to life.  Our estimate was the diamond would need to come down to 1.17ct in order to greatly improve its looks, at least that was our estimate based on our diamond recut chart.

The diamond cutter did what he needed to do and once done it was back to the GIA to see what they thought of it.  Great news for us the stone’s finished weight only dropped down to 1.34ct.  The good news continues as cut grade jumped up three cut grades to excellent.  As a bonus some inclusions were removed from the diamond during the recutting and the GIA increased the clarity grade from VS2 to VS1.

The diamond now is very brilliant and a great piece of art, certainly this stone will grace the finger of a truly beautiful girl at some point.

We will do another recutting ride along shortly.  We had in our inventory a very ugly 3.13ct cushion cut diamond, we did a posting about clarity enhancing using the stone.  After enhancement it was still ugly, so we sent it off to the cutter as well and are expecting it back shortly.   I suspect the transformation of that stone will be even more dramatic than this one.