Have you ever seen a diamond with good HCA and bad idealscope?

[vtx531]

I ask this because the few ones I have been thinking about buying that score well on the HCA have had good idealscope images as well. This leads me to believe that if it is GIA excellent cut, scores well, ex sym then its going to not have a problem with leakage.

So I''ve been looking at Blue Nile now cause they are cheaper than other places for what I''m looking for. Worst comes to worse, I can always send it back.

So my question: how likely is a diamond to be excellent cut, excellent symmetry, good HCA score... and then for some reason have a leakage problem?

-Chris

 

[stone-cold11]

Yes, I have.

 

[Lorelei]

Date: 10/15/2009 11:51:17 AM
Author:vtx531
I ask this because the few ones I have been thinking about buying that score well on the HCA have had good idealscope images as well. This leads me to believe that if it is GIA excellent cut, scores well, ex sym then its going to not have a problem with leakage.

So I've been looking at Blue Nile now cause they are cheaper than other places for what I'm looking for. Worst comes to worse, I can always send it back.

So my question: how likely is a diamond to be excellent cut, excellent symmetry, good HCA score... and then for some reason have a leakage problem?

-Chris

Absolutely I have Chris. It is not that common admittedly, but the ones I have seen have normally scored below 1 and been shallow proportioned stones or ones which are borderline steep deep and or aren't cut tightly especially with the crown and pavilion angle averages being loose and hitting ' leakage zones' in some cases.

 

[Todd Gray]

Of course because the HCA takes the overall proportions into account and is not based upon the facet-by-facet structure of the diamond... The ''average'' measurements which are stated on the lab reports for Crown & Pavilion angle are based on the average of the high and low measurements for each section... The HCA has no way of knowing what those measurements might be and thus the output is based on the average measurements which are entered.

Here''s a real world example from a discussion I was having with a member of PS the other day, we were discussing an ideal scope image for a diamond which according to the GIA lab report has a crown angle of 34.4 degrees and a pavilion angle of 41.0 degrees with a total depth of 61.6% and a table diameter of 56%. Enter these numbers into the HCA and you get a score of 1.7 EX VG VG VG

I asked the person to obtain a Sarin | OGI | Helium report showing the facet-by-facet structure of the diamond and then we were able to determine that the crown angle had a low of 33.7 degrees and a high of 35.1 degrees which is a swing of 1.4 degrees. The pavilion angle had a low of 40.4 degrees and a high of 41.6 degrees which is a swing of 1.2 degrees.

Needless to say that a significant spread between the high and low measurements per section resulted in an ideal scope image which was a bit "Wonky"

Now if the Crown angle was 34.4 degrees with a low of 34.1 and a high of 34.7 and the Pavilion angle was 41.0 degrees with a low of 40.8 and a high of 41.3 degrees AND there was reasonable consistency in the facet-by-facet structure of the diamond in terms of facet shape per section, then the diamond would likely have exhibited a considerably better ideal scope image.