HCA Calculator credibility?

[Ricky Rick]

Hello Everyone, welcome to my first post Apologies in advance if this is a softball question. I knew absolutely nothing about diamonds two weeks ago, and since then I've advanced all the way up to the status of "Not a complete Newbie". Might contradict that momentarily. Long story short, I've been to a couple jewellers (lengthy visits) and have started to narrow down my search, at least a little. I thought I may have found potentially the diamond I was looking for, BUT I discovered the HCA calculator on this site, and now am officially confused.

General overview of the round diamond I was high on, is GIA certified, 1.03 carats, F colour, SI1, EX, EX, EX, no fluorescence. It will have a halo setting and rose gold band. I was curious because the cut aspect is 'excellent' on paper, looked that way with the naked eye in store too, but on the HCA calculator it scored a very poor - 5.5.

I thought excellent cut implied the best light refraction etc, but the HCA score was not good. Can anyone help shed some light on this for me? Thanks!

 

[Karl_K]

Can you post the information here that you entered in the HCA please?
That will help us tell you why the HCA score came out the way it did.
Jewelry store lighting is designed to make any diamond bright and sparky.
They spend a lot of money on it.
It is less diamond friendly lighting that the differences in cut become more apparent.

GIA EX cut grade has a very wide range. It includes some combinations that are world class and some that are not so great.

 

[bmfang]

It comes down to angles, specifically crown and pavilion angles.

GIA XXX is a pretty wide range. One of my wife’s stones is a XXX but only comes out with a 4.4 on HCA.

 

[Ricky Rick]

Can you post the information here that you entered in the HCA please?
That will help us tell you why the HCA score came out the way it did.
Jewelry store lighting is designed to make any diamond bright and sparky.
They spend a lot of money on it.
It is less diamond friendly lighting that the differences in cut become more apparent.

GIA EX cut grade has a very wide range. It includes some combinations that are world class and some that are not so great.

 

[Ricky Rick]

Sure
Depth 62.5%
Table 57%
CA 36%
PA 41%

 

[whitewave]

This is what you want to stay with:
Depth 60-62.3

Table 54-58

Pavilion 40.6 to 40.9

Crown 34-35

 

[bmfang]

Likely to have been pinged by the extremely steep crown angle. For a 36 degree CA on a GIA report, it could be anywhere from 35.76 to 36.24 degrees.

 

[Karl_K]

Sure
Depth 62.5%
Table 57%
CA 36%
PA 41%

The HCA is dinging it for being on the steep/deep side.
GIA grossly rounds the numbers on the report so its not exact but its an indication.
With this one all the combinations in the rounding are still steep/deep.
In favorable lighting as you found it can be very beautiful.
In less favorable lighting a better cut stone could outshine it.

 

[Ricky Rick]

Hmmm, alright thanks for all your help everybody. I will be back online tomorrow as the gf is almost home lol

 

[bmfang]

For the record, GIA takes an average of the 8 CA’s as measured by their scanning machine and then rounds up or down to the nearest 0.5 degree mark. AGS graded stones, it’s just the average of the 8 CAs with no further rounding.

I don’t think GIA do the same thing for PAs though. Just straight average. Those in the trade, pls correct me if i’m wrong.

 

[John P]

I don’t think GIA do the same thing for PAs though. Just straight average. Those in the trade, pls correct me if i’m wrong.

GIA rounding: Nearest 0.5 degrees for CA. Nearest 0.2 degrees for PA. Nearest 5% for stars and lower half lengths. No data provided regarding upper half lengths.

 

[bmfang]

GIA rounding: Nearest 0.5 degrees for CA. Nearest 0.2 degrees for PA. Nearest 5% for stars and lower half lengths. No data provided regarding upper half lengths.

Another tidbit to file away in my brain about Diamonds. No wonder I prefer AGS graded stones more than GIA. Less rounding.

 

[ringo865]

I bet your stone's diameter is smaller than its weight would indicate because of the steep/deep angle combo. Nobody wants a diamond that looks smaller than it should.

OP if you want posters here to help you find a stone online, post your budget and desired specs.

 

[Ricky Rick]

Thanks again for all the input everyone, its extremely helpful. Now for the tricky part potentially, can I mention this finding to my jeweler? Saying I want a stone that falls in a certain range? Or are they just going to say that's hokus pokus or discredit this calculator entirely.

 

[BrimstoneTwo]

Hi Ricky

You are the customer and you decide what you want. You are 100% within your right to tell the vendor exactly what your requirements are. It's not personal. There are certainly vendors who will poo poo these things but you have to decide who you trust. A bunch of strangers online with zero to gain, or a person who directly benefits from the sale. Your call, your money.

 

[ringo865]

And if they won't - or can't - you can come back here for options on stones from vetted online vendors.