HCA tool

[eugchen]

i know the tool is more used as an exclusion factor, and that anything under 2.0 has a high likelihood of an excellent cut diamond with amazing fire. of course this score doesnt indicate anything to do with color or clarity. if you find a decent looking diamond on first look with an excellent polish and cut with GIA papers, but HCA of 4-6, is this a game changer for you guys? or is this the least reliable measurement?

 

[kenny]

If you care about good cut and good light performance ... reject rounds that score over 2.0.
Get an Ideal scope, aka IS, pic on rounds that score 2.0 and under.

Reason: crown and pavilion angles from the lab report are AVERAGES of 8 angles each, around the diamond.
The HCA does not have psychic powers.
It is possible, but unlikely, that all 8 CAs and all 8 PAs are identical.
It's more likely they are not identical.
Exactly HOW wonky they are will be visible in the IS image.

Hope this post wasn't too condescending for you.

 

[gm89uk]

HCA calculates theoretical light leakage. Even at HCA just above 2 this is minimal and there may be many beautiful diamonds (but reflector images essential). Once you get to 4s and particularly 5s, no matter how carefully symmetrical and cut, it just won't look as lively and bright as other lower hca diamonds.

Buying online it's much easier to reject stones above 2 as you significantly reduce your chance of getting a dud.

Have a look at this:
https://youtu.be/Cz3qn2Tx6oI

The far left is a shallow crown but still HCA <2. The far left is your typical 5hca stone (I haven't plugged in the numbers)

 

[whitewave]

4-6 no way!!!!

 

[eugchen]

If you care about good cut and good light performance ... reject rounds that score over 2.0.
Get an Ideal scope, aka IS, pic on rounds that score 2.0 and under.

Reason: crown and pavilion angles from the lab report are AVERAGES of 8 angles each, around the diamond.
The HCA does not have psychic powers.
It is possible, but unlikely, that all 8 CAs and all 8 PAs are identical.
It's more likely they are not identical.
Exactly HOW wonky they are will be visible in the IS image.

Hope this post wasn't too condescending for you.

haha you are funny kenny. ill be the bigger man and ignore that last comment.

 

[eugchen]

forgot to mention this---thank you Kenny for your help.

few other questions---can you get the ideal scope image for most online vendors ,like IDJ, bluenile, zoara, B2C, whiteflash, etc?

is there an easy way to get HCA score? or is it a matter of manually entering in the info on the website?

 

[eugchen]

its pretty amusing, i think alot of these online jewelers discourage HCA, maybe because they are trying to sell poor HCA diamonds...

i got this response directly from Bluenile along with a few others.

"Blue Nile does not use HCA at all. HCA is extremely outdated, and the majority of the diamond industry no longer uses HCA. FYI, the founder of HCA left the company and moved to GIA because he knew HCA could not meet the grading standards of GIA."

 

[kenny]

its pretty amusing, i think alot of these online jewelers discourage HCA, maybe because they are trying to sell poor HCA diamonds...

i got this response directly from Bluenile along with a few others.

"Blue Nile does not use HCA at all. HCA is extremely outdated, and the majority of the diamond industry no longer uses HCA. FYI, the founder of HCA left the company and moved to GIA because he knew HCA could not meet the grading standards of GIA."

Anyone can get 4 numbers (I've read that Crown and Pav angles are more accurate than percentages) from a GIA or AGS report (but not from their cheapest reports ... but 2-carat honkers will have the full report) and plug them into the HCA here:

https://www.pricescope.com/tools/hca

Refusal to offer IS images why I do not recommend Bluenile.

Many good PS vendors offer IS pics in their listing.
I think james allen stopped, which is why I no longer refer posters to them.
I like Whiteflash, goodoldgold highperformancediamonds and briangavindiamonds, though I've only bought from the first two, and was very pleased in every way with them.

You can read about, and buy your own IS, here.

http://ideal-scope.com/?Ref=pricescope

My impression the reason HCA under 2 is not good enough for final selection is the crown and pav angles are averages of 8 angles each around the diamond.
If all 8 happen to be the same, that's groovy.
But, if the 8 angles vary a great deal but happen to average out to good averages, such as 40.8 and 34.7 the HCA (not being psychic) won't know, but the IS (being an actual photograph) will reveal such wonkiness.

I'm glad you are only considering diamonds with grading reports from legit labs now.