These guys could help a lot here. I can only partially help.

The white powder is a harmless substance, but I cannot remember exactly what it is. I think Russ knows. White mandrel release is not only used in India, but also Japanese glass beads and currently produced Czech and Chinese beads.

Sometime around the 1950s - 60s, I believe, the Venetians started to use the wire mandrel production, with acid to dissolve the wire. I have some neat millefiori from that period, and yes, they are matte and with tiny perforations.