HCA & AGA/NAJA Cut class

[dave79]

i just found out some of diamond list excellent cut, but get average result compare to some very good cut with excellent result when using this 2 method. By the way that stone with excellent cut it is excellent? Aren't some very good cut above the level of the excellent. Are this method accurate or the GIA listed wrong

 

[John P]

Different metrics, such as those of GIA and AGSL - as well as predictive systems like HCA and AGA - do share an area where the top grades overlap. But they don't all agree on the exact "bullseye" of best angular combinations.

Pavilion angle is what many consider the most critical element and is good for showing where the ‘centers’ of the different systems lie. For 53-58% tables, you'll find that pavilion angles 40.6-41.0 have the greatest approval cross-system. The AGS cut guidelines suggest most 0 candidates in that range. The HCA and AGA prefer the shallow side of that range and a bit lower; which is why some shallow GIA VG diamonds may get top marks in other systems. The GIA system prefers the steep side and higher; which is why quite a few GIA EX fall outside the criteria of all of those other systems.

 

[dave79]

got it ! but what you will be recommended if buying a diamond base on the GIA Certificate or the result of HCA & ACA ?

 

[John P]

The parameters I personally seek - when buying for myself or a loved one - are in a range that meets the top requirements of all of those categories.