HCA - need more data?

[Manks]

Hi All

I used the search facility on the site to find stones of a given quality. However, I cannot input the results to the HCA because the data provided by the dealers does not include crown or pavilion angles. Is this deliberate or just "protocol"?

Manks

 

[diamondsman]

G.i.a doesnot provide those #'s ,Only under their comments where they specify if the stone has cr.angles Greater than 35% or less than 30%,in most cases that with the information on depth ,table,girdle,etc... could really tell if the stone is got brilliancy.

stay withing these parameters and you will have a nice stone.
D=59-62%
t=53-57%(ideal),-60%
gridle=thin-med-slthick
polish-ex-vg
symm=ex-vg
culet=none
flour=none-faint

 

[Manks]

OK I understand. Am I correct on saying, though, that with the information provided by running a search on this site, it is not possible to accurately use the HCA?

Manks

 

[hoorray]

You are right that many vendors do not list the crown and pavilion angles for their stones, so you can't use the HCA. If you find some stones that meet the rest of the criteria you are looking for, you can contact the vendor and ask for the crown and pavilion angles. Ask for a sarin report. Most will provide it.

 

[pricescope]

Hi Manks,

If crown and pavilion angles are not available (like in most cases with current GIA reports without Sarin or Ogi numbers) you cannot use it.

You can search for the diamonds with known pavilion angles and pre-calculated HCA here: Search by cut quality (known HCA)

 

[valeria101]

If you want to know where one stone stands in the rank for brilliance, you might want to consider that the respective interval of depths and table percentages still allows for not-so-brilliant stones.

HCA is better at weeding out bastards, but not perfect.

The H&A pattern is also a good predictor of light return.

The accurate diagnostic will have to involve the stone itself though, not the (incomplete set of) numbers: BrilliabnceScope and the Ideal Scope come to mind

 

[valeria101]

The chart represents all HCA results possible for stones with 60% depth and 55% table (within the ideal range for these measures alone). All non-red/orange area represent an endless array of lifeless cuts. Since about 40% of the chart area in not within the desirable range: you still have 40% chance to get a really unattractive stone if only taking into consideration table and total depth as selection criteria.