Fabulous finds, Paul! Nor have I seen these before. But they seem very within Venetian ability - a non-glass worker's vision of how they may have been made - looks like a long-ish black base was "wrapped" with black and white striped & twisted glass, then segmented into individual beads. Very interested to hear what others think.

.....And an observation from David...yikes, could it be a new Java variety...the weight of the beads may help to tell you, as new Java would be very light compared with Venetian glass.