When you say black cumin...forgive me for asking this again...but what are you referring to? Sometimes people refer to kalonji, or nigella sativa seeds, as black cumin (I gather erroneously...they are also called black onion seeds). The Indian black cumin is something different (kala jeera)...its not nearly as distinct or potent, in my view, as nigella/kalonji. It also is more of a long, thin, dark gray seed, whereas kalonji are more square or roundish, and very black. Not that kala jeera isn't great, I just find it more subtle.
Kalonji is one of those spices that I am a bit amazed hasn't really made inroads into other world cuisines...it is so distinct, not in a bad, asafetida way, but in a wow, that's tasty and savory sort of way. I used it in a spice rub on some cured, smoked canadian bacon a while back and everytime I hit a bit of kalonji seed I really appreciated the little bit of zippy flavor.