Hi Rosanna, the Kiffa bead you show appears to have been made from 100% powder glass including the core, you may have found it with the Prosser beads but it does not belong to this group. I believe what Floor was trying to say is that the Kiffa makers have, on occasion, used European made beads as the base of their beads, rather than making a powder glass base. This practise of using European glass beads as bases or cores is not limited to Prosser beads, I have numerous examples made on Czech Uranium glass and others, I also have several very rare examples that have Venetian Rosetta beads as a core. The Mauritanian women were not decorating Prosser beads for the Prosser bead companies, they were using a readily available product to speed up their personal bead making. I hope this helps