Hi Christian,
I posted this bead a number of years ago, and the only speculation was that it might be Venetian, probably due to the colors and design. The ends have been ground flat, so it's impossible to say what the original bead looked like. It is about 15.5 mm diameter.
But it appears to be built around a grey, ground glass paste (?) base. Is it possible that a Venetian or other European bead making center used this type of base at some point? Jamey's speculation that maybe the French used this technique is intriguing.
Jamey, you have the most info and interest in this subject. If you would like this bead for study please let me know and I'll send it to you.
Rosanna's bead is on its way to me now, though I have been thinking about it.
The exterior of the bead suggests conventional lampworking and trailing (based on the appearance of the decorations). Yet the center of the bead is granular and gray--suggesting the bead was built around a composition base. But this seems unlikely for an otherwise conventional glass bead.
What if it were actually the opposite?
From my trip to Nigeria in 1998, I know that there were "beadmakers" (actually bead-alterers) who would perform tasks, such as putting broken beads back-together using gray powderglass. This was not a subtle treatment. It was quite obvious. I bought a strand of these beads (that I still have, somewhere).
So now I an wondering whether the intent may have been to reduce the size of the perforation of a conventional glass bead, by introducing gray powderglass into the perforation channel (?). This, of course, need not have been done in Nigeria. Any competent bead-alterer could have done it. And we know that beads are altered in Ghana as well.
I will respond again once I have seen the bead.
JDA.