How do your stones rate on the HCA?

[strmrdr]

You have to remember that the hca is a tool nothing more nothing less.
Like any other tools it has its flaws.
The ags rating system is another tool.
Between the 2 I think that hca is a better tool and study of Rhino’s results for his diamonds will possible prove that.
But like the gia that is trying to reduce the calculations needed to come up with the perfect shape to 8 for something that would need 1000s if not 100000s of parameters it doesn’t take everything into account.
For example it does not take the size and shape of the facet meet points into account.
One diamond with perfect sharp meet points and one with rolled meet points could have the same hca score but would look very different.
Same thing for varied individual facet angles.
Rhino’s optical test results would pick these up because they make a huge difference in appearance but the hca that just uses an average would not.

I could go on but I wont at this time because you should get the idea.

 

[valeria101]

As far as I understand, the relation between spread and light return is somewhat uneasy under HCA standards. Both aparent size and sparkle are desirable, so anyone may expect to have to tradeoff one for another. But does this have to be harsh trading? Mara's stone works light great even if it is not all that deap. Also, there have been attempts to create cuts to improve the appearence of shallow stones (the "royal" fancy cuts come to mind). If there trully is a way to sell lighter, brighter diamonds, why most "bad cuts" are overly deap?

 

[Mara]

Probably because the general buying public is trained to look at carat weight first and other things second. In a jewelers lighting environment, it looks sparkly and guess what? It's 1 carat. That magical mark. Lighter, brighter stones would may only weigh .90c but would look like 1ctw with spread. But it's what it says on the cert that sells the stone.

 

[Manks]

I would not agree with the assessment that larger table =" greater spread. This is not the cast all the time. I can show ya diamonds with ">60 tables that have yucky spread

Rhino

I'd be interested to hear why that might be. Maybe the cut of the star and bezel facets? As spread is to do with optical perception, it should necessarily follow that a table making up a greater percentage of a stone's face up view should give the stone greater spread. If that is not the case, surely other factors are at work to change the way the eye sees the stone.

Correct me of I am wrong.

 

[Garry H (Cut Nut)]

Toska try from here on
http://www.diamond-cut.com.au/11_brilliance.htm

Rhino / Manks - all other things being equal a diamond with a larger table = greater spread.
Thin girdle and then big table and then Lower crownangle and then shallow pavilion is roughly the order of things in real life.

 

[Toska]

Thanks Garry,

I used to always think that http://www.diamond-cut.com.au was the same as the pricescope tutorial, maybe because the template looks almost identical. Now I realise its whole different kettle of fish. I like it!
Much more detail in your site.

I get the idea about a certain score being on the cusp. Do you have a similar table which could be used to assess a diamond with 59.7% table size?

I am trying to work out where my diamond would fit into that diagram, and it seems to be in that blank area between 40.5 and 40.7 pavailion angle.