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how can a hca<2 rock be bad?

a03b

Rough_Rock
Joined
Apr 9, 2016
Messages
14
Hi all, hca is a rejection tool not a selection tool (as far as i have read) but how so?

Let's say we have a vs1 3ex gia diamond with no fluorescence and <hca 2.

Can this be diamond a bad diamond? if yes, how? Or is this as safe as it gets? Thanks
 

tyty333

Super_Ideal_Rock
Premium
Joined
Dec 17, 2008
Messages
21,670
a03b|1463762958|4034028 said:
Hi all, hca is a rejection tool not a selection tool (as far as i have read) but how so?
It means that the diamond has passed the first test/check and now it's time to get an idealscope image (and possibly an aset image).

Let's say we have a vs1 3ex gia diamond with no fluorescence and <hca 2.

Can this be diamond a bad diamond? if yes, how? Or is this as safe as it gets? Thanks
It can still have leakage because the HCA only takes into account 4 values. In reality, in the crown area there are 8 measurements
that all get averaged together. This averaging can cause the stone to come out with a nice score when it's really off on a few angles.
Same thing with the pavilion angle value...there are actually 8 measurements that are averaged. The table size is actually the
average of 4 measurements. So with all this averaging going on sometimes a stone can pass the test ok but still have some
leakage. This diamond may not be "bad" but compared to another stone with similar measurements it might not be as good. This
is why most Pricescopers want Idealscope images of the stone they are interesting in buying. You can check out info here
if you want to learn more about stone measurements.
http://diamondcut.gia.edu/05_diamond_anatomy.html
 

Gypsy

Super_Ideal_Rock
Joined
Aug 8, 2005
Messages
40,198
HCA is not enough as explained above.

Diamond still has to have following:
Table: 60 less
Depth! 59-62.3
Crown:33.5-35
Pavilion: 40.6-40.9

Then its.safer. HCA just tells you if angles are complimentary that's all. If you understand the angles how they work you don't need it because you can do it in your head.

But idealscope is best as that coupled with the above stats it is selection tool.
 

kenny

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
28,175
a03b|1463762958|4034028 said:
Hi all, hca is a rejection tool not a selection tool (as far as i have read) but how so?
Here's how:

The Crown and Pavilion angles input into the HCA are actually averages of 16 angles (8 each) around the diamond.

Each of the 8 may happen to be the same (a good thing) or they may vary a great deal ... but each set of 8 may average out to a good number, such as 34.7 and 40.8.

The HCA has no way of knowing which it is.
That's why an Idealscope pic is needed; It would reveal such wonkiness.

HCA is only step one of the 2-step process.
Step 2 is an IS pic.
 

gr8leo87

Shiny_Rock
Joined
Apr 24, 2015
Messages
381
Also if you magnified image and a reflector image (idealscope or ASET) that indicates light return you don't need HCA.

Even when you have awesome idealscope picture with a 0.5 HCA score - many stones would still be 'rejectables' (sounds good) according to PS standards if stones have their crown angles below 33.5. So in strict senses Neither idealscope or ASET scope are selection tools if you don't understand the actual numbers.

Sent from my Nexus 4 using Tapatalk
 

Gypsy

Super_Ideal_Rock
Joined
Aug 8, 2005
Messages
40,198
gr8leo87|1463781413|4034163 said:
Also if you magnified image and a reflector image (idealscope or ASET) that indicates light return you don't need HCA.

Even when you have awesome idealscope picture with a 0.5 HCA score - many stones would still be 'rejectables' (sounds good) according to PS standards if stones have their crown angles below 33.5. So in strict senses Neither idealscope or ASET scope are selection tools if you don't understand the actual numbers.

Sent from my Nexus 4 using Tapatalk
Or iif stone is deeper than 62.4
 

Gypsy

Super_Ideal_Rock
Joined
Aug 8, 2005
Messages
40,198
Clarity of VS1 and no fluorescence, incidentally do NOT a nice stone make. AT ALL. In fact they aren't even on the list of things you need. And many experienced shoppers will not even WANT those things.

You get an eyeclean SI1 with strong blue as long as the stone is eyeclean and not overblue, you are talking a seriously stunning stone.
 

a03b

Rough_Rock
Joined
Apr 9, 2016
Messages
14
Gypsy|1463783043|4034174 said:
Clarity of VS1 and no fluorescence, incidentally do NOT a nice stone make. AT ALL. In fact they aren't even on the list of things you need. And many experienced shoppers will not even WANT those things.

You get an eyeclean SI1 with strong blue as long as the stone is eyeclean and not overblue, you are talking a seriously stunning stone.
Thanks all, didn't know those figures were averages. It makes sense now.

Gypsy, I thought fluorescence was not a desired property. (Though I know some people like the blue hue)
 

Gypsy

Super_Ideal_Rock
Joined
Aug 8, 2005
Messages
40,198
Please go up to knowledge tab at top of screen a d read fluorescence tutorial. :wavey:
 
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