Indeed, Jamey, these beads are from a big sack which was to be discharged as the content was exchanged for sand. It was found by Arianna Giuman, a young lady living in Murano, whose family took over an old, small glass factory. She told me a tale about making so fine canes: they were drawn vertically instead of orizontally as usual. I spoke with many learned (in glassmaking) people in Murano, and all of them told me it was just a tale. Months ago I found an old man who told me the same history: he saw vertically drawing canes at the Societą Veneziana per l'Industria delle Conterie, whose factory was more than 20 metres high.
After some researches, Gianni Moretti, of E.Moretti & F.lli from Murano, discovered that a cousin of him many decades ago bought from the Societą Conterie, and never used, a machine to vertically draw canes for beads like these.

Ciao,
Giorgio