Black diamond engagement rings are not the most common of engagement rings. After all, the color black suffers from social stigma of being closely related to bad luck, to death, and to other undesirable forebodings.

i still don't see the value of black diamonds over onyx or obsidian.  one of the most valued and unique aspect of diamonds are the refraction of light, something black diamonds are not so much about.

Interestingly enough I was thinking the same thing.  I'd take the natural black any day over the treated.  I am curious too how they would sparkle compared to a dark quart or the like.  I know that they (in lighter colors) do not have anywhere near the punch as a diamond, but does the dark color make it impossible to see the difference?

We must also understand that black diamonds, are used mainly for pavé, tennis bracelets, riviere, etc etc...
I think, just from a business perspective, it is unnecessary to use expensive natural black diamonds, lackluster and rough, less attractive to "commercial" customers.

On large stones, you can enjoy different perspectives.
I don't think there is a smoke quartz effect, I think it's the transparency that is around the crown, due to the thin material. As glass, thin is transparent solid is green.

This is "The Spirit of DeGrisogono" 312,24 ct - is the world's largest cut black natural diamond

Aahahaha I agree... for Drag-queens. But this is OT 

i just think it's one of those useless and sad traits of humanity that we take name over function; a diamond is a highly prized thing, which people pay a large premium for, so if you can call it a diamond you can charge a lot for it.  if it looks like a duck, and quacks like a duck, why would you pay for a swan?