HRD vs GIA&HCA

[Anthonyd]

Okay, I have been harping on this topic on another forum, mainly because there seems to be a great deal of different opinions. I was dumbfounded when I was informed (on this board) that a diamond that I was considering may not be as great as I thought. It was certified by HRD as being cut "very good" (their highest score)

I posted all the information and numerous people told me that it in fact was a very poorly cut stone. It was no where in the Towolsky range, was not "AGS IDEAL" and recommended I don''t buy it. I was shocked, how can HRD grade it in the highest regard, and every other method gave it a poor score?

So I researched and posted and have not come to a straight answer yet. I looked up the HRD website and did some reading there. The website has their specs on cut listed but it is difficult to read, but another site I found had it listed more concisely. Please read and let me get your input:

http://www.diamonds.icestore.com.au/diamonds-diamond_information.htm

http://www.diamonds.icestore.com.au/diamonds%20-%20Ideal%20Cut.htm

On the first link please see the chart at the bottom. Are there any experts that can make sense of that?

 

[Anthonyd]

Some interetsing reads, I hope an expert comes across this thread to comment on these links:

http://www.diamondsandopals.com/diamonded/diacert.php?r=other

http://www.nationwidejewellers.com.au/diamondgrading.htm

http://www.antwerpdiamonds.be/diamonds-faq.htm

*For the last link read the "some misunderstandings" part*

 

[denverappraiser]

HRD Very Good Cut means the following:

Crown angle 30.7-37.7
Pavillion angle 39.6-42.2
Table 53 – 66
Crown % 11-16
Pavillion depth 41.5 - 45
Girdle Thin to slightly thick
Culet: None to small
Total Depth; 55.5 – 63.9

Most of the people here use the term ‘Ideal’ to describe stones with AGS0 proportions. The standards for AGS0 are:

Crown Angle: 33.7 – 35.8
Pavillion angle: 40.2 – 41.2
Table: 52.4 – 57.5
Crown % 14.6-15.7
Pavillion depth % 42.2 – 43.8
Girdle: Thin – Medium
Culet: None to small
Total Depth: Not discussed

Both labs also have standards for polish and symmetry in order for a stone to be awarded the described grade.

These definitions are substantially different. The AGS rules are quite a bit narrower and with the exception of table size, are entirely a subset of the HRD rules. The HRD system uses slightly different language to describe girdle and culet and I’ve converted them to make comparison easier.

GIA doesn't offer a cut grade at all although they do supply some of the required information.

The rules of the HCA are fairly complicated but you can get an HCA grade by using the above dat and the 'cut adviser' under Tools at the top of the page. If you want to learn the rules for the grading, they are explained at the HCA Site

Neil Beaty, GG ISA
Independent Appraisals in Denver

 

[Garry H (Cut Nut)]

IGI more or less use the same scale.

On demand they will use Ideal and Excellent, these grades fit inside the Very Good.

It has taken some time to bring about changes to these simplistic number based approaches.
Final AGS have seen the light and all their Ideal-Cuts will get great HCA scores.
You can read about it in other active threads.