Understanding and evaluation after HCA < 1.0

[teobdl]

Background:
Within HCA 0-2, many prefer scores of 1-2 rather than 0-1. A percentage of diamonds with HCA 0-1 may look brilliant at a distance (say, 3 feet), but may go dark at closer distances due to obstructing/obscuration where the observer blocks light that otherwise would have been reflected. This specific obstruction phenomenon is not as prevalent among diamonds with HCA 1-2.


Questions:
1. Is the background that I've written accurate?
2. What is the prevalence of diamonds with HCA 0-1 that display this obstruction phenomenon?
3. What is the prevalence of diamonds with HCA 1-2 display this phenomenon?
4. Can existing technologies identify diamonds that would be prone to this close-distance-obstruction phenomenon?
5. Short of in-person evaluation in varied light conditions, what is the single best technology (or combination of technologies) that would help make a selection for light performance alone?

 

[teobdl]

For example, this diamond scores HCA 0.7. How could one discern if it displays the phenomenon described above without seeing it in person?
http://www.briangavindiamonds.com/d...-ags-c-104061069089#!prettyPhoto[gallery2]/1/

 

[pomellina]

Can you link me to any posts discussing this phenomenon or research - however amateur - into it? I'd be interested to read it.

 

[teobdl]

Just wanted to *bump* this thread because it didn't get a response (slow Sunday)!

To boil it down to one question, if a diamond scores < 1.0 on HCA, is there a technology (idealscope, ASET) or something else that could potentially let you know whether it will be subject to the obstruction phenomenon in which it goes very dark at close distances?

 

[JulieN]

The evaluation of HCA < 1.0 is the same as it is for 2.0: IdealScope or ASET and a trusted vendor.

See the reference picture for "Very Shallow" http://ideal-scope.com/1.using_reference_chart.asp

Ideal Scope will show more black under the table and at the arrow tips.