Thanks Napoleone,
I think, it would be a good explanation, because, this bead is actually not cut as the others. That was the question for me. I have never seen this kind of bead with this cut, in Africa. The edges are smooth whereas that this has a frank cutting which does not exist in the traditional trade beads which circulated in Africa. Your explanation seems to me more likely. I did not know this kind of bead, and it is the only one whom I have never found in Africa.
Thanks very much!