Heart and Arrow with high HCA score

[stitch]

I just went to two local stores and look at 3 H&A stones. They all look beautiful under H&A scope. However they all have HCA score above 3. How is it possible?

 

[John P]

The C/P combinations are steeper than the HCA will predict <2.0

More details?

 

[stitch]

I don''t remember the information. They are all GIA certified H&A. I look at each certificate and confirm the notion of H&A. However I got the "...only buy if the price is right" notion after I input all required information. Is this normal for H&A?

 

[John P]

Date: 10/24/2009 11:18:23 PM
Author: stitch
I don't remember the information. They are all GIA certified H&A. I look at each certificate and confirm the notion of H&A. However I got the '...only buy if the price is right' notion after I input all required information. Is this normal for H&A?

H&A is simply 3D alignment of facets and their opposites. It is possible for a diamond to have great 3D alignment, but with primary angles (crown and pavilion) outside the range that is optimum for light return. What you have then is a diamond which can look nice in the H&A viewer, but it will show light leakage if placed under ideal-scope or ASET.

One must separate the notion of H&A (cut precision) from angles necessary for great light return (cut performance).

It used to be that cutters who produced H&A were focused as much or more on those great angles - usually near-Tolkowsky's angles. As a result most H&A diamonds were synonymous with great performance. But cut precision and cut performance do not always occur together.

Over the years tools have improved and so the number of diamonds with close-to or pretty-good H&A patterns has increased... Unfortunately the most popular grading system for rounds (GIA's) includes some pavilion and crown combinations in the EX grade which are deeper than many experts like (reflected in the HCA and other metrics). As mass manufacturers learn to "game" the system we're seeing more diamonds with nice 3D cut precision, but an increase in the ones cut to angles which save more weight but reduce performance.

 

[stitch]

In situation like this, is the performance that includes "Light Return, Fire , Scintillation, Spread" more important than H&A? If we have to choose, what do you think we should go for?

 

[John P]

Date: 10/24/2009 11:43:05 PM
Author: stitch
In situation like this, is the performance that includes ''Light Return, Fire , Scintillation, Spread'' more important than H&A? If we have to choose, what do you think we should go for?

Yes: A diamond with angles that produce the best light return is most attractive to most people. The addition of H&A 3D precision in such diamonds can sharpen contrast and produce larger virtual facets, making sparkle more visible & intense in some lighting conditions.

But in diamonds that do not produce good light return to begin with the presence of H&A makes little visible difference.

 

[Lorelei]

John has you covered!

 

[stitch]

Thanks John and Lorelie. I acquire another important knowledge from experts like both of you