The minor facets make a minor difference

[Garry H (Cut Nut)]

Some organizations and individuals claim that the minor facets are more important to the appearance and desirability of round brilliant cut diamonds than I believe to be the case.

GIA for instance says that because “up to 50% or more” of the diamonds surface is made up of the minor facets. In their last ‘ fire’ article they produced many charts showing the importance of the minor facets. Careful examination of the scales used on those charts however might indicate more about the politics of the competition between GIA vs. AGS labs.
http://www.gia.org/research/1383/2281/article_detail.cfm
http://www.gia.org/research/1383/1505/article_detail.cfm this last link shows one of those charts. The range of minor facets charted are outside those normally encountered.
The GOG website features a lot very useful information, but Jonathon too has helped spread the story that the minor facets count, as has RockDoc.

I want to make it clear that I too believe the minor facets have an important role. E.g. combinations like large table with shorter lower girdle facets make for an improvement and help compensate for otherwise perhaps less attractive stone. However I believe their role is sometimes overplayed for politics or commercial gain. I do not say that to protect the HCA system, which I have no plans to develop to account for their effects. Symmetry has a much larger role to play than minor facets in terms of HCA, but I still have an intuitive feeling that perfect symmetry may not be the only and most important way to achieve a nice diamond. The Ideal-Scope remains the quickest and simplest way to account for both variations.

These DiamCalc2 generated images of virtual diamonds and their cut quality calculations make my point about the crown facets.

 

[Garry H (Cut Nut)]

There is more difference here in the case of the 75% example, 75% lower girdles are quite rare though - most stones on the market are between 80 and 85%.

The 75% LG stone will show more fire, which is not yet given as a DC result.

(BTW these are measured as length not height which would be slightly shorter numbers).

 

[Garry H (Cut Nut)]

Here is the Ideal-scope images along side.
Sorry I forgot them.

 

[Stephan]

Yes, the most beautiful H&A I saw have short lower girdles...
Better life and better fire...

 

[Rhino]

Greetings,

You knew I'd respond to this one.

You see ... I think they are all beautiful my friend. I base my conclusions on the minor facets much becuase of the same reasons GIA has. GIA conducted their study with the HUMAN EYES of many participants (I too was invited to the study to be a participator but time would not allow the Rhino). So while I find there is a certain appeal to diamonds with shorter stars/lower girdle combos I personally have a preference towards the longer star/lower girdle combo. I too have conducted the identical study that GIA has except not with people in the industry but with common lay people. People who wanted to purchase a super ideal cut diamond and wanted to make the comparison for themselves.

Perhaps to you and I Gary, who see many beautiful stones (realizing how much garbage there is out there) appreciate both flavors of super ideals (and the many inbetween) but in this case I have to point to John Q. Public, who in over 95% of those who have made the comparisons have picked the longer star/lg combo in a blind Pepsi challenge. Those who come to our store get to do this if they so desire. I love doing it with our clients. I will also say there are some who don't see much of a difference too.

I agree with your statement as well that the lower girdles have the greatest impact on the appearance of all the minor facets. Moreso than the stars.

Peace,
Rhino

 

[Rhino]

----------------
On 7/13/2003 5:33:30 AM Stephan wrote:
Yes, the most beautiful H&A I saw have short lower girdles...
Better life and better fire...----------------

Stephan,

Have you ever personally compared 2 H&A diamonds ... one with 80-82% lower girdle height (76-78% length) and 58-63% stars next to another H&A with 77-78% lower girdle height (74-75% length) with 45-50% stars?

Peace,
Rhino

 

[Garry H (Cut Nut)]

I made a mistake and put in an 85% lower girdle stone with the default 46.1% DiamCalc star crown ratio. Sorry.
Note the 85% has .03 less contrast and .01 less stereo light return now.

For the record the star ratios were set at 50:50 and the first post – the crown ratios - were done with 82% lower girdles. Octonus may have picked a winner there?

Thanks for responding Jonathon / Rhino. I agree it is very much a personal thing.

Except that GIA did their virtual research first and then set about proving it with observation studies.
And I am with you re lay people - who cares what the trade prefer? They bring so much historical baggae with them. They can not for instance help but reject diamonds with feature flaws they can identify - eg large tables, shallow crowns etc.

 

[Stephan]

Jonathan,
The only H&A I could see here had all longer star facets.
Some had shorter, some had longer lower girdles.
But your website is the best documentation, and I like the pictures and Bscope of diamonds with shorter lower girdles (I will not say a brand).
Have a nice day!