Is HCA applicable to AVR and OEC stones?

[qwedsy]

The subject line sums up my question. Is an AVR/OEC with an HCA over 2 a no go?

 

[Rhino]

Good question. In brief no.

The technical reason being is this.

The HCA was developed by Garry primarily inspecting modern round brilliant cut diamonds whose lower half facet length extend considerably under the table facet (75%+ in length). When pavilion main angles in modern round brilliant cuts exceed 41 degrees coupled with crown angles that are 34.x+ degrees which many rounds have, it produces stark light leakage under the table facet as the lower halves become the areas of blatant leakage.

Since OEC diamonds (and AVR's for that matter) are not dependent upon lower half facet reflections under the table, the HCA is basically moot when it comes to inspecting them. Pavilion angles in OEC's that are greater than 41 degrees "work" when coupled with proper crown angles of course. There could, in essence be another HCA for OEC's (not yet developed) but the 2 would not be compatible as OEC's require completely different proportion sets to accomplish the goal of ideal optics. Other optical technologies however (ASET, IdealScope) can reveal valuable information about OEC's which are helpful in the cut analysis.

Kind regards,
Rhino

 

[Karl_K]

No it isn't.
In an oec/AVR the mains drive light turn in a modern RB the pavilion half/girdle facets drive much of the light return.
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

 

[qwedsy]

Thank you Rhino and Karl_K, that cleared it up perfectly! Again a bit more educated for my diamond hunt.

 

[OECsareforLovers]

Have you seen this screening chart for OECs?

https://www.pricescope.com/journal/screening_chart_old_european_cut_diamonds

 

[qwedsy]

I had not. Thank you!