Flanders Cut Certs & Dimensions

[foolintherain]

First, I would like to thank all who participate in this site, especially the folks at goodoldgold.com, dbof.com, and niceice.com.

This is mostly a question for Jonathan at goodoldgold, but I will open it up to the forum. (For those who haven''t seen his site, he has a wonderfully educational collection of pictures and diamond evaluations.)

I have been looking at Jonathan''s (goodoldgold.com) evaluations of Flanders cut diamonds. In every case where there is both a lab cert and his own evaluation, his eval shows the Length and Width at ~10% less than the lab cert. For instance, there is an educational 1.01 Ct Flanders with a GIA cert that says 6.36 x 6.34 mm. The Good Old Gold Analysis says the diamond is 5.78 x 5.79 mm. These dimensions are 9% smaller (0.57 & 0.56 mm).

Between the educational diamonds and the ones he has for sale, there are 5 PGS certs, 2 HRD certs, and 1 GIA cert.

I then looked at 2-3 dozen diamonds of different shapes (round, radiant, princess, emerald, regent) and never saw this--every one of his measurements matches up within a couple hundredths of a milimeter.

Can anyone explain what is going on here?

 

[foolintherain]

For those interested, I have been obsessing about this because I have already put down a $1000 deposit on a $6000 ring, and I am starting to be very concerned.

I doug up every cert I could find on Flanders diamonds. They were mostly PSG and HRD, but I found a couple GIA, too. I then compared these to certs on various rounds from bluenile.com and mondera.com. I looked at 33 0.91 ct rounds (because my diamond is a 0.91 ct.) I then looked at a less diligent sampling of each carat weight for which I have a flanders cert.

In every case, the Flanders cert has a length and width that approximates that of the average round brilliant of the same weight. The flanders' total depth tended to be slightly greater than that of rounds.

Now, Flanders cut diamonds also go by the name Elara. On the Elara website, they explain that each short side of this cut is 1/2 the length of the long side. Given some algebraic calculations, the area of the girdle of a flanders cut will be 24% greater than that of round with the same dimensions. I will attach a picture of this in the next post.

Based on the Certs that I have reviewed, here is the mathmatical annomoly...

1) Flanders have 24% greater area at their girdle than a comparably sized round.
2) Flanders tend to have slightly greater depths than rounds with same length,width and weight.

This really doesn't seem to add up.

 

[foolintherain]

File mentioned in the above posting

 

[foolintherain]

After looking at my last post, a possible solution is that the flanders length and width has been measured from short side to short side. I have not done the math the prove that this reconciles things, but it seems to make more since. Still if this is case, it doesn't really sit with me all that well.

 

[foolintherain]

So the math works out to be an 8.3% difference in length when measured from short side to short side in comparison to measuring from long side to long side (and there is some rounding error in there.) This seems to explain what I originally observed as a 10% difference.

Assuming that I did all of this right, I must say I still don't like it much.

In HRD's defense, their certs specifically call out "Flander's Brilliant" and show the diamond with the short edges on the top and sides. On the other hand, GIA calls the stone a "cut cornered square modified brilliant" and shows it with the long sides on the top and sides. It seems odd to me that a "square" diamond would have length and width measured across diagonals (princess diamonds are not measured this way.)

 

[diane5006]

HI Jonathan will be the best person to answer your question...I am sure he will as soon as he can (I think he is still on vacation)...or maybe one the the GG's who post here will have some information...

I believe that GIA refers to Flanders, Regent, etc as modified square brilliant...

Best of luck,

 

[Richard Sherwood]

Hi Foolin. Those labs are measuring from the short corners, while Jonathan is measuring from the long sides.

In my opinion, the long side measurement is more appropriate and more correct, but I believe the short corner measurement is the one used because of the founder's conception of the orientation of their cut, as shown below.

 

[foolintherain]

To sum up:

1) The flanders cut really is a beautiful cut (hence all the effort). If you want a square cut with the brilliance of a round, they are worth looking at.

2) To translate dimensions from certs into the opposite orientation, multiply them by 0.892.

3) At the girdle, a flanders has ~93% of the area of an equivalently sized round.

4) Some of the extra weight is carried in a slightly lower pavillion (they average about 2% lower--about 0.1 mm @ 1 ct)

5) They also have very steep crown angles at an average of 43% compared to rounds at 35%.

6) Their crown height is comparable to a round if you use the narrow Length/width (14.6%), but a bit lower at 13% if you use the longer length/width from the cert (I don't know which is preferable).

 

[overflowing]

Hi Foolin,

Thanks for the tips! I''m also looking for a Flanders cut. Do you know what the ideal Depth % and Table % is for a flanders?

Thanks.