question re: using HCA

[jackson]

Is it possible to use the HCA if one has crown angle and pavillion %, or pavillion angle and crown % ??? Or do both anges OR both %''s need to be entered?
Just asking, since some sites, reports give different information.............

 

[Regular Guy]

Just to say back what Garry H., creator of this scale, has said...angles are better.

My diamond had output associated with it for both angles and %s. I think the problem with %s is that rounding will more typically happen with that data. The output for my diamond was similar, regardless of the data points, but slightly different for 2 of the 3 different scenarios.

For example, for all 3 combinations reviewed below, the score on factors was consistently: ex, ex, ex and vg. However...

with either just angles, or Crown angle plus pavilion %, the score was .9 and FIC
but with pavilion angle and crown %, the score changed to 1 (no big change) but it became TIC!
and with all %s, it was back to .9, but again changed from FIC to TIC.

Keeping in mind that measurement variation may skew the best of data, working with what you got seems to be reasonable. Note, all output above is fairly consistent, with all representing a "go" decision, and although I understand angles are better when you have them, any data seems workable for the purpose.

The original data is immediately below, for which I applied this analysis.

Now let's see what we report back to Joey on his question, also asked recently, to put all this data in perspective.

Proportions:
Depth 62%
Table: 55%
Girdle: medium to slightly thick, faceted
Culet: none (or, .7 v. small)
Crown: 35.8' 16%
Pavil: 40.1' 42%

Best wishes!

 

[Garry H (Cut Nut)]

You can use mixed data, but angles for both are better.

But remeber that a great HCA means the stone can be very very nice, but if the symmetru=y and other factors are average, the stone may be only nice. If the stone has lousy symmetry and messed up minor facets, then it could be not so desirable.

An ideal-scope image will clear away further doubt.

 

[jackson]

Which facets are most important for providing brilliance? I know crown angle affects fire.......

 

[Garry H (Cut Nut)]

All need to be working together - but leakage is mainly a factor of pavilion angle

 

[rosy]

Hi,
What pavillion angle degree(s) would cause light leakage?

 

[Garry H (Cut Nut)]

It depends on the crown angle.
I can not make it simple because it is not.
www.diamond-cut.com.au could help