Need help on 4 diamond's GIA certificates and HCA score.

[IdeenDiamond]

Hi, so I'm trying to buy a diamond to set for my gf. I'm talking with a private seller and he has sent me some certificates. They are all ~1.7ct rounds with F/SI2 and excellent cut. The one I wanted (CM-569) seems really great. But when I plug it into the http://www.pricescope.com/tools/hca tool it gives me a terrible score that's over well over 2 (it's like a 6). I noticed @Kenny had been referring to that link a lot. Should I stay away from this stone?





I have the certificate of 3 other diamonds, none of them scores that well. They are all excellent cut, polish, and symmetry, so can this HCA number really be that important? I have photos of the other 3 as well, I'll post if need be.



Alternative 1


Alternative 2


Alternative 3



Thanks in advance!

 

[kenny]

Here's the only 'help' you need on HCA scores:

Reject rounds that score higher than 2.0 on the HCA.
Get an Idealscope pic on those scoring under 2.0.
Compare the diamond's Idealscope pic to this chart.

The reason you need an IS pic is the Crown and Pavilion angles you input to the HCA are averages of 8 angles around the diamond.
That average number may be the average of 8 identical angles (a good thing) or 8 angles that vary all over the place but AVERAGE OUT to a good average (a bad thing) ... this will be evident in a non-symetrical IS pic.

http://ideal-scope.com/reference-chart-ideal-scope-images/

 

[IdeenDiamond]

So you're saying that stone that has a HCA score of 6 will be obviously bad to the naked eye? Especially compared to stones sold in store, like Robin's Brothers for example (I'd assume most big brick and mortars are selling good stones).

What do I tell my seller? I just say "hey I tested something called a HCA score and it came out bad."

Thanks!

 

[pfunk]

Look at the example of a "poor" diamond on the chart that kenny posted. See how there is a ring of leakage under the large facet on the crown of the diamond called the table facet? The good stones look red in that area while the bad ones have a white ring of light being leaked through the diamond and not being returned to your eye. Now look at the photo of the diamond you posted. Look at the table facet (center of diamond shaped like an octagon). You will notice all around the outer part of the table there is a ring of gray color that matches the background of the diamond. This is the ring of leakage that you see on the "poor" idealscope example stone. You are seeing straight through the diamond to the background. The stone will end up less bright in that area because the light doesn't come back to your eye. I will post a link later to a good old gold video that will show you very clearly the visual difference between a leaky and nonleaky diamond.

Edit: here is the link to a good video. Long, but very good info for you to start out with.

https://m.youtube.com/watch?v=VlO68vmqkRs

Also, from what you have listed, the first alternative would be what I would consider the best of that group and the one most likely to perform well.

 

[JDDN]

Your assumption that most brick and mortar stores are selling good stones is not necessarily true!

Please search previous threads on this topic on PS.

You are spending a lot of money no matter what your budget is and you should get a stone that is extremely well cut and beautiful.